Catalyst for preparing graphene and method for preparing graphene

Abstract

The invention discloses a catalyst for preparing graphene and a method for preparing graphene. The catalyst comprises the following components in parts by mass: 5-80 parts of metal copper, 0-20 parts of metal iron and 5-80 parts of third metal, wherein the total mass of the catalyst is 100 parts; and the third metal is selected from at least one of magnesium, titanium, vanadium, chromium, manganese, cobalt, zinc, bismuth, palladium, gold, silver, nickel, tungsten, molybdenum, tin, cadmium, platinum and gallium. The catalyst is heated to a molten liquid state, the feed gas is blown out from the bottom of the liquid catalytic medium, and graphene and hydrogen are generated through cracking in the bubble rising process under the combined action of high temperature and the catalyst. The density of the generated graphene is far lower than that of a liquid catalytic medium, and the generated graphene spontaneously floats on the surface, so that the phenomenon that a traditional catalytic cracking catalyst is easy to deactivate due to carbon deposition is effectively avoided. And meanwhile, no carbon oxide emission is generated in the cracking process, low-carbon and high-value utilization of natural gas resources is realized, and the added value of a natural gas industry chain is extended.

Description

Technical Field

[0001] The invention relates to the field of carbon material preparation by catalytic cracking of natural gas, and in particular to a catalyst for preparing graphene and a method for preparing graphene. Background Art

[0002] Graphene is a two-dimensional carbon material with a single atomic layer arranged in a hexagonal lattice. It was first produced by sticking a thin sheet of graphite with tape in 2004. Due to its excellent physical properties, such as high electrical conductivity, good thermal stability, excellent mechanical strength and fascinating chemical properties, graphene has been a hot topic in academia and industry.

[0003] In recent years, graphene preparation technologies have emerged in an endless stream. At present, Hummers redox method and liquid phase exfoliation method are commonly used methods for large-scale preparation of graphene, but the graphene prepared by these two methods has problems such as uneven quality, high defect density, low purity and small size. In contrast, chemical vapor deposition is a method for producing high-quality large-size graphene, but its yield is low and cost is high, and it is still difficult to meet the low-cost preparation needs of high-quality graphene. Other methods, such as epitaxial growth method and arc discharge method, cannot achieve low-cost preparation of high-quality graphene. Therefore, high-quality, large-scale, low-cost graphene production is still a bottleneck problem facing the field of graphene applications.

[0004] At present, various circles have actively explored the low-carbon, low-cost and large-scale production of graphene, but most of them remain in the theoretical conception and laboratory stage, and there are still many challenges in industrial production.

[0005] CN112938895A uses metals Sn, In, Ga and Pt, Bi, Pd and their alloys as molten liquid catalytic media, but its product can only be carbon black, which has low added value and limited application. Compared with graphene products, the economic benefits brought are orders of magnitude different.

[0006] CN116332129A proposes a green hydrogen preparation system and process. The scheme introduces graphene generation, but it mainly describes a new design system and a process. Although it briefly mentions in the specific implementation that graphene can be produced by molten metal Cu or Cu-Bi alloy, its catalyst components are significantly different from those of the present invention, and the cracking reaction temperature needs to be at least 1100°C, which greatly increases the energy consumption of the reaction process.

[0007] CN111333057A proposes a reaction device for preparing graphene and a method for preparing graphene, wherein any one of Bi-Ni binary alloy, Fe-Ce binary alloy catalyst, Ni-Ce binary alloy catalyst and Bi-Ni-Ce ternary alloy catalyst is used to realize graphene preparation, and the catalyst design is significantly different from the present invention.

[0008] CN109107533A proposes a process for preparing graphene activated carbon from corn stalks and uses metallic copper as a liquid-phase catalytic medium. In order to keep the metallic copper melted, the reactor temperature is within the range of 1050-1500°C, which is bound to increase system energy consumption and the resulting greenhouse gas emissions, and is not suitable for industrialization. Summary of the invention

[0009] The object of the present invention is to provide a catalyst for preparing graphene and a method for preparing graphene. The catalyst is a catalyst that can produce high-quality graphene continuously on a large scale at low cost.

[0010] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0011] In one aspect, the present invention provides a catalyst for preparing graphene, wherein, based on 100 parts by total mass of the catalyst, the catalyst comprises the following components in mass fractions: 5 to 80 parts by mass of metallic copper, 0 to 20 parts by mass of metallic iron, and 5 to 80 parts by mass of a third metal;

[0012] The third metal is selected from at least one of magnesium, titanium, vanadium, chromium, manganese, cobalt, zinc, bismuth, palladium, gold, silver, nickel, tungsten, molybdenum, tin, cadmium, platinum and gallium.

[0013] According to the catalyst of the present invention, preferably, the catalyst comprises: 60-80 parts by mass of copper, 0-10 parts by mass of iron (more preferably 5-10 parts by mass) and 10-40 parts by mass of a third metal; more preferably, the catalyst comprises: 70 parts by mass of copper, 5 parts by mass of iron and 25 parts by mass of the third metal.

[0014] Another aspect of the present invention provides a method for preparing graphene, the method comprising the following steps:

[0015] Add the components of any of the above catalysts into the graphite tube and mix them evenly;

[0016] The graphite tube is placed in a reaction container, and protective gas is introduced into the graphite tube from the bottom to exhaust air; then, reducing gas is continuously introduced, and the catalyst is heated and melted to obtain a molten metal alloy;

[0017] Continue to raise the temperature to the temperature required for the reaction and then maintain the temperature, then introduce raw gas from the bottom of the graphite tube into the liquid phase layer of the molten metal alloy therein, the raw gas is a carbon-containing gas; the introduced raw gas bubbles in the liquid phase layer to form small bubbles, and the bubbles begin to crack and produce hydrogen and graphene under the combined action of high temperature and catalyst during the rising process. Graphene spontaneously floats on the surface of the liquid phase layer because its density is much lower than that of the molten metal alloy, and graphene is obtained by collecting it.

[0018] The carbon-containing gas is introduced as the raw gas into the liquid phase layer of the molten liquid metal, and a large number of bubbles are continuously formed. At this time, the bubbles can be regarded as catalytic substrates. Graphene grows on the surface of the bubbles and is brought to the surface of the liquid phase layer as the bubbles rise. The molten liquid metal plays a catalytic and heat-conducting role. On the one hand, the high-temperature molten metal provides the necessary heat for the cracking reaction. On the other hand, the catalytic property of the metal helps to reduce the reaction energy barrier and join the reaction process. Due to the unique properties of the molten liquid metal and its homogeneous catalytic ability, its active components are no longer confined to a specific area but are in a free-moving state, which effectively avoids the traditional catalytic cracking carbon deposition, catalyst deactivation and other phenomena, and realizes the long-term stable operation of the catalyst. At the same time, the cracking process (CH 4 →C+H 2 ) does not produce any CO x emissions and achieve low-carbon and high-value utilization of natural gas resources.

[0019] It is worth noting that due to the splashing and evaporation of the molten metal, some small metal particles exist on the prepared graphene. However, due to the obvious density difference between metal particles and graphene, most of the metal particles can be removed by physical separation, such as water washing; when the prepared graphene sample is mixed with water, the metal particles will settle to the bottom of the water. After physical separation, the graphene is placed in FeCl 3 The metal is etched and potential oxides are removed in a solution and an HCl solution. Thereafter, the obtained product is washed with acetone, ethanol and deionized water, filtered and dried to obtain pure graphene.

[0020] According to the method for preparing graphene of the present invention, preferably, after collecting the graphene, post-processing is also included, and the post-processing includes:

[0021] The collected graphene is washed with water to remove small metal particles;

[0022] Graphene is placed in FeCl 3 Metal etching and potential oxide removal are carried out in solution and HCl solution; then pure graphene is obtained through washing, filtering and drying.

[0023] More preferably, the FeCl 3The concentration of the solution is 0.8 mol / L to 2 mol / L, such as 1 mol / L; the mass concentration of the HCl solution is 10% to 30%, such as 10%. Further preferably, in the FeCl 3 The drying temperature is preferably 100-115°C, for example 105°C.

[0024] In the method for preparing graphene of the present invention, the raw gas is a carbon-containing gas, such as a mixture of one or more fuel gases containing hydrocarbons such as natural gas; preferably natural gas; further, it can be diluted natural gas, which can be diluted with nitrogen, or with functional hydrogen, helium, neon, etc. In order to further increase the hydrogen concentration in the product, hydrogen-diluted natural gas is preferably used as the raw gas. The volume concentration of natural gas in the raw gas can be 1% to 100%, preferably 40%.

[0025] According to the method for preparing graphene of the present invention, preferably, the temperature required for the reaction is 700-1600°C, more preferably 1100°C.

[0026] The present invention can adjust the metal components and their ratios in the catalyst to make the cracking reaction temperature of the raw gas within the range of 700-1600°C, with strong adaptability; and thereby improve the adaptability range of the natural gas concentration (1%-100%) in the raw gas.

[0027] According to the method for preparing graphene of the present invention, preferably, the components of the catalyst are pretreated before mixing; the pretreatment includes: washing the components with acetone, ethanol and deionized water in sequence, and then drying for standby use. The pretreatment is used to remove impurities, dust and organic pollutants on the surface of each metal to maintain the cleanliness of the metal catalyst.

[0028] According to the method for preparing graphene of the present invention, preferably, the protective gas is selected from at least one of nitrogen and inert gas (helium, argon, neon, etc.), more preferably nitrogen. In the process of heating and melting the catalyst, the protective gas is introduced to exhaust the air, and the reducing gas is introduced to ensure that the metal is in a reducing gas atmosphere to avoid high-temperature oxidation of the metal during the heating and melting process. Preferably, the reducing gas is hydrogen.

[0029] According to the method for preparing graphene of the present invention, preferably, before the raw gas is introduced, it is ensured that the air is exhausted, specifically by detecting the exhaust gas by a gas chromatograph to determine whether there is still oxygen.

[0030] According to the method for preparing graphene of the present invention, preferably, a small hole is opened at the bottom of the graphite tube for passing the protective gas, reducing gas and raw gas. It is understood by those skilled in the art that the small hole can be the same, and the protective gas and reducing gas are passed into the graphite tube through the small hole; after reaching the reaction temperature, the raw gas is replaced; the small hole can also be set to two or three to pass different gases; the present invention does not limit the number of small holes.

[0031] According to the method for preparing graphene of the present invention, preferably, the reaction vessel is a methane cracking device;

[0032] The methane cracking device comprises a quartz tube and a graphite tube, wherein the graphite tube is placed inside the quartz tube, and a heat insulating material is arranged between the side walls of the two tubes, wherein the heat insulating material is mainly used to isolate and reduce the heat radiation of the graphite tube to the quartz tube; an inductor coil which can move up and down is arranged outside the quartz tube for heating; by adjusting the height of the inductor coil, the heating position of the inductor coil just surrounds the position of the graphite tube;

[0033] The quartz tube is provided with a side tube above the upper end of the graphite tube and connected to a collecting bin for collecting graphene; when a certain amount of graphene floating on the surface of the liquid phase layer of the molten metal alloy accumulates and reaches the position of the side tube, it will be automatically collected from the side tube to the collecting bin;

[0034] The top of the quartz tube is provided with an air outlet; the bottom of the graphite tube is provided with a small hole for inputting protective gas, reducing gas and raw material gas into the graphite tube.

[0035] More preferably, the small hole at the bottom of the graphite tube is connected to a gas mixing tank, and the gas mixing tank is connected to the gas storage devices of the protective gas, the reducing gas and the raw gas.

[0036] More preferably, an outlet is provided at the bottom of the collecting bin, and a valve is provided at the outlet to transfer the collected graphene for subsequent post-processing.

[0037] The beneficial effects of the present invention include:

[0038] 1) It solves the problem of rapid deactivation of traditional natural gas catalytic cracking catalysts due to carbon deposition, enabling them to maintain catalyst activity for a long time, with the characteristics of large-scale and continuous production of graphene, avoiding frequent start-up and shutdown of the device.

[0039] 2) Compared with the existing molten methane / natural gas cracking graphene catalytic system, which has high reaction temperature (>1200°C) and low methane intake concentration (<20%), this catalytic system can flexibly adjust the binary or multi-element alloy catalytic ratio to make its cracking reaction temperature applicable in the range of 700-1600°C, has strong adaptability, and improves the adaptability range of methane intake concentration (1%-100).

[0040] 3) Only hydrogen and graphene are generated during the entire cracking process, without other CO x It reduces greenhouse gas emissions and has significant economic and environmental benefits, namely, it realizes the low-carbon and high-value utilization of natural gas resources.

[0041] 4) Compared with the traditional methane / natural gas steam reforming hydrogen production process, it has a shorter process flow.

[0042] 5) Compared with the traditional graphene preparation method, the present invention can not only realize the mass production of graphene, but also greatly reduce the production cost of graphene. It is expected to reduce the cost of preparing graphene powder by CVD method on the market by more than 60%, and realize low-cost or zero-cost hydrogen production. The graphene produced is of higher quality than that of redox method and liquid phase exfoliation method.

[0043] 6) The present invention is not only applicable to catalytic cracking systems using methane / natural gas as raw materials, but is also suitable for cracking systems of other carbon-containing gases; based on the above, the present invention has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic diagram of a methane cracking device used in an embodiment of the present invention;

[0045] Figure 2a This is an electron microscope image of graphene before purification in Example 1;

[0046] Figure 2b This is an electron microscope image of graphene after purification in Example 1;

[0047] Figure 3a This is the graphene scanning electron microscope result obtained in Example 1;

[0048] Figure 3b This is the graphene scanning electron microscope result obtained in Example 2;

[0049] Figure 3c This is the graphene scanning electron microscope result obtained in Example 3;

[0050] Figure 3d The graphene scanning electron microscope result image obtained for comparative example 1;

[0051] Figure 4The graphs are the Raman analysis results of graphene obtained in Examples 1, 2, 3 and Comparative Example 1;

[0052] Figure 5 Graphene specific surface area test result diagram obtained in Example 1;

[0053] Figure 6 XRD analysis result of graphene prepared in Example 1.

[0054] Description of reference numerals:

[0055] 1. Gas mixing tank, 2. Thermal insulation material, 3. Graphite tube, 4. Quartz tube, 5. Air outlet, 6. Graphene, 7. Collection chamber, 8. Valve, 9. Catalyst metal alloy, 10. Induction coil, 11. Bubbles. DETAILED DESCRIPTION

[0056] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0057] All numerical specifications herein (e.g., temperature, time, concentration, and weight, etc., including ranges for each thereof) are generally approximate values ​​that may be appropriately varied (+) or (-) in increments of 0.1 or 1.0. All numerical specifications may be understood as being preceded by the term "about."

[0058] In the following specific examples, the operations involved were carried out under conventional conditions or conditions recommended by the manufacturer if the conditions were not specified. The raw materials used were conventional products that can be purchased on the market if the manufacturers and specifications were not specified. Among them, metal copper, iron, magnesium, titanium, vanadium, chromium, manganese, cobalt, zinc, bismuth, palladium, gold, silver, nickel, tungsten, molybdenum, tin, cadmium, platinum, and gallium were purchased from Hegners Metal Materials Co., Ltd.

[0059] The following examples adopt Figure 1 The methane cracking device shown in the figure is carried out, and the methane cracking device includes a quartz tube 4 and a graphite tube 3. The graphite tube 3 is placed in the quartz tube 4, and a heat insulating material 2 is arranged between the side walls of the two. The heat insulating material 2 is mainly used to isolate and reduce the heat radiation of the graphite tube 3 to the quartz tube 4; an inductor 10 that can move up and down is arranged on the outer shell of the quartz tube 4 for heating; by adjusting the height of the inductor 10, the heating position of the inductor 10 just surrounds the position of the graphite tube 3. The quartz tube 4 is provided with a side tube above the upper end of the graphite tube 3, and is connected to the collection bin 7 for collecting graphene; when the graphene floating on the surface of the liquid phase layer of the molten metal alloy accumulates to a certain amount and reaches the position of the side tube, it will be automatically collected from the side tube to the collection bin 7.

[0060] The top of the quartz tube 4 is also provided with a gas outlet 5; the bottom of the graphite tube 3 is provided with a small hole for inputting protective gas, reducing gas and raw gas into the graphite tube. The small hole at the bottom of the graphite tube is connected to a gas mixing tank 1, and the gas mixing tank 1 is connected to the gas storage device of the protective gas, reducing gas and raw gas, and valves are provided on the connecting pipelines. The bottom of the collection bin 7 is provided with an outlet, and the outlet is provided with a valve 8; it is used to transfer the collected graphene for subsequent post-processing.

[0061] Example 1

[0062] 1) The metal components in the catalyst required for the experiment are cleaned with acetone, ethanol and deionized water in turn to remove impurities, dust and organic pollutants on the surface and maintain the cleanliness of the metal catalyst. Then, it is dried for use.

[0063] 2) If Figure 1 As shown, 70 parts by mass of copper, 5 parts by mass of iron and 25 parts by mass of the third metal (tin) are weighed and put into the graphite tube 3 and mixed evenly. The size of the graphite tube is 10 cm in outer diameter, 8 cm in inner diameter, 2 cm in bottom thickness and 30 cm in total height. The graphite tube 3 is placed in the quartz tube 4 of the methane cracking device, and the space between the quartz tube 4 and the graphite tube 3 is filled with the heat insulation material 2, where the heat insulation material 2 mainly isolates and reduces the heat radiation of the graphite tube 3 to the quartz tube 4. By adjusting the height of the inductor 10, the heating position of the inductor 10 just surrounds the position of the graphite tube 3.

[0064] Open the inert gas nitrogen valve, set its gas flow rate to 300mL / min, the gas passes through the gas mixing tank 1, and then enters the inside of the graphite tube 3 through the small hole at the bottom of the graphite tube, and continues for 30 minutes to replace the air in the reaction chamber. Subsequently, the total gas flow rate is maintained at 300mL / min, and the reducing atmosphere hydrogen valve is opened at the same time, and the gas flow rate is set to 15mL / min, the inert gas nitrogen flow rate is reduced to 285mL / min, and the heating device (inductor 10) is turned on to melt the catalyst metal alloy 9 under the reducing atmosphere. Set the heating power to 1.5kW, the induction coil 10 starts to heat the graphite tube 3, and as the temperature continues to rise, the metal particles in the graphite tube begin to melt gradually. After melting, keep the temperature constant for 30 minutes to make it fully mixed, and the liquid phase layer depth of the catalyst metal alloy 9 after melting is about 24cm. Then continue heating until the required reaction temperature of 1100°C is reached.

[0065] After reaching the reaction temperature of 1100°C, close the reducing atmosphere hydrogen valve, open the raw gas natural gas valve, and control the methane volume concentration to 40% (using nitrogen for dilution) by adjusting the natural gas flow.

[0066] The gas bubbles in the liquid phase layer of the catalyst metal alloy 9 to form small bubbles 11. During the rising process, the bubbles 11 begin to crack to produce hydrogen and graphene 6 under the combined action of high temperature and catalyst. The generated graphene 6 floats spontaneously on the surface of the molten catalyst metal alloy 9 because its density is much lower than that of the molten catalyst metal alloy 9. When a certain amount is accumulated, it is discharged from the side tube of the reaction tube into the collection chamber 7. The gas product is discharged from the outlet 5 at the top of the quartz tube 4.

[0067] The graphene collected in the collection bin 7 is post-processed and purified, and the valve 8 is opened to transfer the collected graphene, and the graphene is washed with water (the metal particles will settle at the bottom of the water) to remove the metal particles doped on the graphene 6. After physical separation, the coarsely sieved graphene is placed in a prepared 1 mol / L ferric chloride solution and stirred for 8 hours under magnetic stirring to etch away the residual metal. After the corrosion is completed, the filtered graphene is placed in 10% HCl and stirred for 8 hours to remove possible hydroxides and oxides. Thereafter, the obtained product is washed and filtered three times in succession with acetone, ethanol and deionized water, and the filter cake is dried at 105°C for 6 hours to obtain pure graphene.

[0068] Example 2

[0069] Similar to Example 1, Figure 1 As shown, 80 parts by mass of copper and 20 parts by mass of tin are weighed and put into a graphite tube and mixed evenly. After melting, the height of the metal liquid phase layer is maintained at 24 cm. Methane cracking reaction is carried out under the same reaction conditions. The obtained carbon material is subjected to a similar purification treatment as mentioned above to obtain a relatively pure carbon material.

[0070] Example 3

[0071] Similar to Example 1, Figure 1 As shown, 70 parts by mass of copper, 5 parts by mass of iron, 15 parts by mass of tin and 10 parts by mass of manganese are weighed and put into a graphite tube and mixed evenly. After melting, the height of the metal liquid phase layer is maintained at 24 cm, and a methane cracking reaction is carried out under the same reaction conditions. The obtained carbon material is subjected to a similar purification treatment as described above to obtain a relatively pure carbon material.

[0072] Comparative Example 1

[0073] Similar to Example 1, Figure 1 As shown, a metal Cu-Bi alloy is used as a catalytic medium, the liquid phase layer is filled to a depth of 24 cm after the metal is melted, and the molar ratio of Cu to Bi in the alloy is 1: 1. Under the same reaction conditions, a methane cracking reaction is carried out, and the obtained carbon material is treated by the same purification method as in Example 1, thereby obtaining a relatively pure carbon material.

[0074] Table 1 shows the comparison results of various parameters of Example 1, Example 2, Example 3 and Comparative Example 1. As can be seen from Table 1, under the same reaction conditions, the catalytic system of the present invention has higher methane conversion rate and hydrogen selectivity than the comparative example.

[0075] Table 1 Performance comparison between Example 1 and Comparative Example 1

[0076] Example 1 Example 2 Example 3 Comparative Example 1 Methane conversion rate % 68.2 67.6 68.4 66.8 Hydrogen selectivity % 97.1 96.6 97.4 95.2

[0077] Figure 2a and Figure 2b This is a comparison of the electron microscope results before and after graphene purification in Example 1. Figure 2a and Figure 2b It can be seen that due to the evaporation and splashing of liquid metal, fine metal particles are deposited on the graphene surface, resulting in the reduction of the quality of the carbon material. After the above purification method is used, it can be clearly observed that the metal particles in the carbon material are eliminated and the purity of the carbon material is improved. The same phenomenon can also be found in Example 2, Example 3 and Comparative Example 1.

[0078] The results of scanning electron microscopy characterization of graphene obtained in Example 1, Example 2, Example 3 and Comparative Example 1 are as follows: Figure 3a , Figure 3b , Figure 3c , Figure 3d As shown. Figure 3a-3c and Figure 3d In contrast, under the same experimental conditions, the characterization results of the graphene carbon materials obtained all showed a flake structure, but Figure 3d The graphene sheet structure is obviously poorer and more disordered, with small spherical agglomerates accumulated in the middle, indicating that the quality of the carbon material is relatively poor.

[0079] Figure 4 The Raman spectra of the graphene samples prepared in Example 1, Example 2, Example 3, and Comparative Example 1 are shown. In the Raman spectrum, the G peak represents the E2g mode of the C=C vibration mode in the graphene structure, which is a typical feature of graphene. The D peak is the Raman active characteristic peak of the graphene C=C bond stretching vibration brought by amorphous carbon. Therefore, the size of the ID / IG ratio is a key indicator for evaluating the integrity and defects of the graphene structure. The D peak (~1350cm -1 ) and G peak (~1580cm -1 The intensity ratio ID / IG can be used to qualitatively analyze the quality of graphene. Figure 4 It can be clearly seen that the ID / IG values ​​of the graphene prepared in Example 1, Example 2, and Example 3 are significantly better than those in Comparative Example 1. Figure 3a-3d The scanning electron microscopy results once again demonstrated that the graphene prepared by the catalytic system of the present invention has better quality.

[0080] It is worth noting that the ID / IG of graphene produced by the catalytic system of the present invention (such as Example 1) is about 0.3, while the ID / IG of most commercial graphenes is in the range of 0.7 to 2, indicating that the graphene of the present invention is of good quality. In fact, the weaker D peak here may be mainly caused by the wrinkles of the graphene, not the intrinsic defects of the graphene itself. -1 The 2D peak at the position can be fitted as a single peak. Generally speaking, a single peak 2D peak is a typical feature of single-layer graphene. In addition, the number of layers (N) in graphene can also be measured by the 2D peak (84.08 cm -1 ) and the following relationship:

[0081] FWHM(2D)=(-45·(1 / N)+88)

[0082] From the above formula, it can be calculated that N is about 12. The results show that the present invention successfully synthesizes high-quality multilayer graphene materials.

[0083] Figure 5 The specific surface area of ​​the graphene prepared in Example 1 is shown. The theoretical specific surface area of ​​a single-layer graphene is 2630 m 2 / g, and because the interlayer interaction will reduce the surface area, the specific surface area of ​​multilayer graphene is much smaller. In the present invention, the measured specific surface area of ​​multilayer graphene is 182m 2 / g, which indicates that its thickness is about 15 atomic layers.

[0084] Figure 6 The XRD spectrum of the purified graphene sample of Example 1 is shown. It can be seen that a diffraction peak at 2θ=26.382° appears, which is a typical feature of parallel-arranged graphene layers. In addition, no other peaks are found in the XRD spectrum, which further indicates that there are no residual impurities in the purified graphene.

[0085] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A catalyst for preparing graphene, in, Based on 100 parts of the total mass of the catalyst, the catalyst comprises the following components in mass parts: 5 to 80 parts by mass of metallic copper, 0 to 20 parts by mass of metallic iron, and 5 to 80 parts by mass of a third metal; The third metal is selected from at least one of magnesium, titanium, vanadium, chromium, manganese, cobalt, zinc, bismuth, palladium, gold, silver, nickel, tungsten, molybdenum, tin, cadmium, platinum and gallium.

2. The catalyst according to claim 1, in, The catalyst comprises: 60 to 80 parts by mass of copper, 0 to 10 parts by mass of iron and 10 to 40 parts by mass of a third metal.

3. A method for preparing graphene, in, The method comprises the following steps: Add the components of the catalyst according to claim 1 or 2 into a graphite tube and mix them evenly; The graphite tube is placed in a reaction container, and protective gas is introduced into the graphite tube from the bottom to exhaust air; then, reducing gas is continuously introduced, and the catalyst is heated and melted to obtain a molten metal alloy; Continue to raise the temperature to the temperature required for the reaction and then maintain the temperature, then introduce raw gas from the bottom of the graphite tube into the liquid phase layer of the molten metal alloy therein, the raw gas is a carbon-containing gas; the introduced raw gas bubbles in the liquid phase layer to form small bubbles, and the bubbles begin to crack and produce hydrogen and graphene under the combined action of high temperature and catalyst during the rising process. Graphene spontaneously floats on the surface of the liquid phase layer because its density is much lower than that of the molten metal alloy, and graphene is obtained by collecting it.

4. The method according to claim 3, in, After collecting the graphene, post-processing is also included, and the post-processing includes: The collected graphene is washed with water; Then the graphene is placed in FeCl 3 Metal etching and potential oxide removal are carried out in solution and HCl solution; then pure graphene is obtained through washing, filtering and drying.

5. The method according to claim 4, in, The FeCl 3 The concentration of the solution is 0.8 mol / L to 2 mol / L, and the mass concentration of the HCl solution is 10% to 30%.

6. The method according to claim 4, in, The graphene is sequentially deposited on the FeCl 3 The solution and HCl solution were treated for 5 to 10 hours respectively.

7. The method according to claim 3, in, The raw gas is natural gas or natural gas diluted with nitrogen or hydrogen; The volume concentration of natural gas in the raw gas may be 1% to 100%.

8. The method according to claim 3, in, The temperature required for the reaction is 700-1600°C.

9. The method according to claim 3, in, The components of the catalyst are pretreated before mixing; the pretreatment includes: Each component was cleaned with acetone, ethanol and deionized water in turn, and then dried for use.

10. The method according to claim 3, in, The protective gas is selected from at least one of nitrogen and inert gas, and the reducing gas is hydrogen.

11. The method according to claim 3, in, A small hole is provided at the bottom of the graphite tube for introducing the protective gas, reducing gas and raw material gas.

12. The method according to claim 11, in, The reaction vessel is a methane cracking unit; The methane cracking device comprises a quartz tube and a graphite tube, wherein the graphite tube is placed inside the quartz tube, and a heat insulating material is arranged between the side walls of the two tubes; an inductor coil which can move up and down is arranged outside the quartz tube to heat the position where the graphite tube is located; The quartz tube is provided with a side tube above the upper port of the graphite tube and is connected to a collecting bin for collecting graphene; and an air outlet is provided at the top of the quartz tube.

13. The method according to claim 12, in, The small hole at the bottom of the graphite tube is connected with a gas mixing tank, and the gas mixing tank is connected with the gas storage devices of the protective gas, the reducing gas and the raw material gas.

14. The method according to claim 12, in, The bottom of the collecting bin is provided with an outlet, and the outlet is provided with a valve.

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