Ethanol-regulated layered metal oxide, preparation method thereof and application of ethanol-regulated layered metal oxide in preparation of single-walled carbon nanotubes by catalytic cracking of methane

Abstract

The invention discloses an ethanol-regulated layered metal oxide, a preparation method thereof and an application of the ethanol-regulated layered metal oxide in preparation of a single-walled carbon nanotube by catalytic cracking of methane, alkali liquor and soluble metal salt containing Fe, Mo, Mg and Al are dropwise added into an alkaline ethanol aqueous solution to form a precipitate, and the ethanol-regulated Fe-Mo / MgAl-LDOs catalyst is obtained after aging, drying and calcining. The catalyst is applied to methane catalytic cracking to prepare the single-walled carbon nanotube. According to the technical scheme, the dispersity of active components in the layered metal oxide is effectively improved, the layered metal oxide has larger specific surface area and pore diameter, but the pore volume is reduced, and the situation that growth of SWCNTs stops due to wall collision in the growth process is effectively avoided.

Description

Technical Field

[0001] The present invention relates to the field of catalyst technology, and more specifically, to a novel inorganic functional material with a layered structure and its application in preparing single-walled carbon nanotubes by cracking methane. Background Art

[0002] Single-walled carbon nanotubes (SWCNTs) possess excellent optoelectronic, mechanical, and other properties, and have broad application prospects in electronics, biology, energy, and the environment. Common methods for preparing SWCNTs include arc discharge, laser ablation, and chemical vapor deposition (CVD). While arc discharge and laser ablation can effectively produce SWCNTs with perfect structures and high graphitization, the high-temperature evaporation used in these methods can lead to the formation of amorphous carbon, carbon-encapsulated metal nanoparticles, and multi-walled carbon nanotubes, making them difficult to scale up. In contrast, CVD, with its relatively mild carbon nanotube growth conditions and advantages such as low cost and good controllability, is widely used for the large-scale synthesis of SWCNTs.

[0003] Since transition metals Fe, Ni, Co, and Mo have high carbon solubility, they are often used as active components for the preparation of single-walled carbon nanotubes. Single-walled carbon nanotube growth requires not only good dispersion of active metal components on the catalyst support and a suitably large BET surface area, but also layered double hydroxides (LDHs), also known as hydrotalcite-like materials, are two-dimensional nanostructured materials based on the layered structure of brucite (Mg(OH)2) with a BET surface area of up to 1289 m 2 / g can be used as a new catalyst for the growth of single-walled carbon nanotubes. Fe is relatively inexpensive, and during the calcination process, Fe easily forms a strong interaction with the support, effectively preventing the catalyst from sintering during the reaction, which can lead to the formation of larger single-walled carbon nanotubes and even the formation of multi-walled carbon nanotubes.

[0004] Currently reported methods for preparing layered metal oxides suffer from uneven distribution of active components during the preparation process, and the catalyst is prone to carbon deposition and deactivation during single-walled carbon nanotube growth. Furthermore, some active sites are insufficiently exposed, reducing the utilization of active species and leading to lower single-walled carbon nanotube yields. This present invention, for the first time, proposes replacing deionized water with ethanol as the co-precipitated solution during the preparation of layered metal oxide catalyst precursors, effectively improving the uneven distribution of active components in the catalyst. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology. In view of the uneven distribution and insufficient exposure of the active components of the catalyst in the existing technology, the catalyst sintering during high-temperature reaction causes the diameter of the single-walled carbon nanotubes to increase and the yield to decrease, and to provide a new inorganic functional material with a layered structure and its preparation method and application in the preparation of single-walled carbon nanotubes by methane cracking.

[0006] This invention effectively improves the dispersion of active components in layered metal oxides. Furthermore, the catalyst prepared using this invention exhibits a more uniform distribution of active components after H2 reduction. Due to this unique layered structure, the active components in the resulting metal oxide after calcination can form strong interactions with the support. Furthermore, the high dispersion of the active components prevents sintering into larger particles, reducing the diameter of single-walled carbon nanotubes and achieving a more concentrated diameter distribution.

[0007] The technical purpose of the present invention is achieved through the following technical solutions.

[0008] Ethanol-regulated layered metal compound and preparation method thereof, i.e., a novel inorganic functional material with a layered structure and preparation method thereof, wherein:

[0009] Ethanol regulates the layered metal oxide to be Fe-Mo / MgAl-LDOs layered metal oxide. Under the regulation of ethanol, the active components have high dispersion. The particles of the active components of the prepared layered metal oxide inorganic functional material are smaller and more uniform after reduction, the specific surface area is improved, and the pore volume and average pore size distribution are maintained.

[0010] The molar ratio of the four elements is Fe:Mo:Mg:Al=x:y:2:1, and x and y are between 0.025-0.5, preferably 0.025-0.2, and more preferably 0.1-0.2.

[0011] Specific surface area is 220-260m 2 / g, preferably 230-260m 2 / g. Pore volume is 0.8-1.2cm 3 / g, preferably 0.9-1.1cm 3 / g. The average pore diameter is 15-32 nm, preferably 17-31 nm.

[0012] The preparation method of ethanol-regulated layered metal oxide (i.e., ethanol-regulated Fe-Mo / MgAl-LDOs layered metal oxide) is carried out according to the following steps:

[0013] Step 1, stirring ethanol as a titration solution at 60-80° C., and when the temperature is stabilized at 60-80° C., adjusting the pH of the ethanol titration solution to 8.0-11.0 with alkaline solution;

[0014] In step 1, the alkali solution is an aqueous solution of sodium hydroxide and sodium carbonate. For example, a predetermined amount of sodium hydroxide and sodium carbonate is weighed and added to deionized water to dissolve them; the concentration of sodium hydroxide is controlled at 0.10-0.30 mol / L, and the concentration of sodium carbonate is controlled at 0.6-1.0 mol / L.

[0015] In step 1, measure 20-50 mL of anhydrous ethanol as the solution to be titrated.

[0016] In step 1, the stirring speed is 100-300 revolutions per minute.

[0017] In step 1, the pH is adjusted to 9.0-11.0.

[0018] Step 2, adding the soluble metal salt solution and the alkali solution dropwise to the mixed solution obtained in step 1 while stirring, maintaining the temperature at 60-80° C., and controlling the pH at 8.0-11.0;

[0019] In step 2, the alkali solution is an aqueous solution of sodium hydroxide and sodium carbonate. For example, a predetermined amount of sodium hydroxide and sodium carbonate is weighed and added to deionized water to dissolve them. The concentration of sodium hydroxide is controlled at 0.10-0.30 mol / L, and the concentration of sodium carbonate is controlled at 0.6-1.0 mol / L.

[0020] In step 2, the pH is controlled to 9.0-11.0.

[0021] In step 2, the stirring speed is 100-300 revolutions per minute.

[0022] In step 2, the dripping speed of the soluble metal salt solution should be controlled within a range of 1 drop per 2 seconds to 2 drops per 1 second; and the dripping speed of the alkali solution should be controlled according to the pH change of the reaction system during the entire reaction process.

[0023] In step 2, corresponding soluble metal salts are weighed according to the ratio of the four metal elements, and deionized water is added to dissolve them to form a soluble metal salt solution, and the total metal ion concentration is controlled at 0.20-0.50 mol / L; the soluble metal salts are ammonium molybdate, ferric nitrate, magnesium nitrate, and aluminum nitrate.

[0024] Step 3: After the addition is completed, continue stirring and aging for 1-15 hours, then stop stirring, and age the obtained precipitate in a 40-80°C water bath for 1-15 hours, filter, wash, and dry the precipitate to obtain a precursor;

[0025] In step 3, the stirring speed is 100-300 revolutions per minute, and the stirring aging time is 10-15 hours.

[0026] In step 3, the aging temperature is 60-80° C., and the aging time is 10-15 hours.

[0027] In step 3, the drying temperature is 60-120° C., and the drying time is 8-24 hours.

[0028] Step 4: Grind the precursor obtained in step 3 and then calcine it. In an air atmosphere, start from room temperature of 20-25° C., heat it at a rate of 1-5° C. / min to 300-450° C., and keep it warm for 1-5 hours; then heat it at a rate of 1-5° C. / min to 500-900° C., keep it warm for 1-5 hours, and finally cool it to room temperature of 20-25° C. with the furnace to obtain an ethanol-regulated Fe-Mo / MgAl-LDOs catalyst (i.e., Fe-Mo / MgAl-LDOs layered metal oxide, or Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material).

[0029] In step 4, starting from room temperature of 20-25°C in an air atmosphere, the temperature is raised at a rate of 1-2°C / min to 400-450°C and kept at this temperature for 3-4 hours; then the temperature is raised at a rate of 1-2°C / min to 600-700°C and kept at this temperature for 2-3 hours, and finally cooled to room temperature of 20-25°C with the furnace.

[0030] In step 4, a muffle furnace is selected for calcination.

[0031] The present invention utilizes ethanol-modulated layered metal oxides in the catalytic cracking of methane to produce single-walled carbon nanotubes. During the entire process, the ethanol-modulated Fe-Mo / MgAl-LDOs catalyst is reduced with H2 to further improve the dispersion and utilization of the active components in the catalyst.

[0032] The specific steps are as follows:

[0033] Step 1: Weigh a predetermined amount of ethanol to regulate the layered metal oxide as a catalyst in an ark, and heat the ark to a reduction temperature in an inert protective atmosphere in a tube furnace at a flow rate of 50-80 mL / min; the reduction temperature is 500-600 degrees Celsius;

[0034] Step 2, introducing H2 for reduction, such as for 30-60 min, with a H2 flow rate of 30-60 mL / min;

[0035] Step 3: Turn off H2 and raise the temperature to the reaction temperature in an inert protective atmosphere at a flow rate of 50-80 mL / min; the reaction temperature is 800-1000 degrees Celsius;

[0036] Step 4: adding methane for reaction, with a reaction time of 30-60 min and a methane flow rate of 10-30 mL / min;

[0037] Step 5: Turn off the methane and cool the furnace under an inert protective gas atmosphere to obtain single-walled carbon nanotubes.

[0038] In the above technical solution, the inert protective gas or atmosphere is nitrogen, helium or argon.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The catalyst produced by the ethanol-regulated Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material under ethanol regulation exhibits uniform distribution of active components, excellent catalytic activity, and high selectivity for single-walled carbon nanotubes. The preparation method of the ethanol-regulated Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material features a simple process flow, a highly innovative metal oxide catalyst, low raw material costs, and ease of regulation, facilitating the large-scale industrial application of methane cracking to produce single-walled carbon nanotubes.

[0041] 2. In the present invention, Mo species acts as an active species auxiliary agent, and undergoes an "avalanche-like" reduction during the reduction process, which greatly improves the dispersion and utilization of the active components and increases the yield of single-walled carbon nanotubes.

[0042] 3. The ethanol-modulated Fe-Mo / MgAl-LDOs layered metal oxide catalyst described in this invention significantly improves single-walled carbon nanotube selectivity compared to conventional metal oxide catalysts. The catalyst's performance can be further enhanced by varying the Fe / Mo ratio and calcination temperature. Compared to other catalysts, this catalyst offers advantages such as low cost, simple preparation, high selectivity, and high activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Element distribution pictures of the embodiments of the present invention and the comparative example.

[0044] Figure 2 This is a SEM photograph of Example 1 in the examples of the present invention.

[0045] Figure 3 1 is the XRD spectrum of Example 1 and the comparative example in the embodiments of the present invention.

[0046] Figure 4 This is an element distribution picture of Example 1 in the embodiments of the present invention.

[0047] Figure 5 Graph showing the BET test results of Example 1 and the comparative example in the embodiments of the present invention.

[0048] Figure 6This is a graph showing thermogravimetric test results of the product produced by using Example 1 of the present invention as a catalyst to prepare carbon nanotubes.

[0049] Figure 7 This is the H2-TPR characterization diagram of the catalyst prepared under different titration environments in the examples of the present invention.

[0050] Figure 8 This is a TEM photo of single-walled carbon nanotubes prepared using the catalyst prepared in Example 1 of the present invention.

[0051] Figure 9 This is a graph showing the Raman test results of single-walled carbon nanotubes prepared using the catalysts prepared in Example 1 and the comparative example of the present invention. DETAILED DESCRIPTION

[0052] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0053] Example 1

[0054] An ethanol-regulated Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material is prepared by the following steps:

[0055] Step 1, weigh 0.0883g (NH4)6Mo7O 24 , 0.2020gFe(NO3)3, 2.5641gMg(NO3)2, 1.8757gAl(NO3)3 are dissolved in 40mL of deionized water to obtain a soluble metal salt solution (or nitrate solution), with the molar ratio of the four elements Fe:Mo:Mg:Al=0.1:0.1:2:1;

[0056] Step 2: Weigh 1.0 g of NaOH and 8.7492 g of Na2CO3 and dissolve them in 100 mL of deionized water to obtain an alkaline solution.

[0057] Step 3, measure 40 mL of anhydrous ethanol as the solution to be titrated;

[0058] Step 4: Place the solution to be titrated in a 60°C water bath and stir. When the dispersion stabilizes at 60°C, adjust the pH of the dispersion to 10.0±0.05 with the alkaline solution obtained in step 2.

[0059] Step 5: Add the nitrate solution and alkali solution dropwise into the pH-adjusted dispersion solution while stirring in a 60°C water bath. During the addition, the pH is controlled at 10.0±0.05, and the nitrate is added at a rate of 1 drop per second.

[0060] After the addition is complete, stirring and aging are continued for 10 hours. Stirring is then stopped and the resulting precipitate is aged for another 10 hours in a 60°C water bath. The precipitate is then filtered, washed, and dried to obtain a catalyst precursor. Deionized water is used for washing, and the drying temperature is 60°C for 10 hours.

[0061] Step 6: Grind the precursor in a mortar and then place it in a muffle furnace for calcination. After cooling, the ethanol-regulated Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material is obtained.

[0062] In step 6, the calcination method is to place the ground precursor powder in an ark, and in an air atmosphere, start from room temperature, heat it at a rate of 1°C / min to 400°C, and keep it warm for 3 hours; then heat it at a rate of 2°C / min to 600°C, keep it warm for 2 hours, and finally cool it with the furnace to obtain Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material.

[0063] like Figure 2 As shown, (a) corresponds to the Fe-Mo / MgAl-LDOs layered metal oxide precursor obtained by titration in ethanol; (b) corresponds to the Fe-Mo / MgAl-LDOs layered metal oxide obtained by titration and calcination in ethanol. It can be seen that calcination does not change the layered hydroxide of FeMoMgAl layered hydroxide, and at the same time, dehydration obtains Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material.

[0064] like Figure 3 As shown in (a), the XRD spectra of Fe-Mo / MgAl-LDOs layered metal oxide precursors prepared in water and ethanol respectively by the method of the present invention indicate that the layered hydroxide (Mg 0.667 Al 0.333 )(OH)2(CO3) 0.167 ·0.5H2O, and has good crystallinity, and ethanol has no effect on the structure of the layered hydroxide; (b) XRD spectra of Fe-Mo / MgAl-LDOs layered metal oxides prepared in water and ethanol respectively using the method of the present invention. The FeMoO4 characteristic peak at 18.9° of the Fe-Mo / MgAl-LDOs catalyst prepared in ethanol disappears, indicating that the Fe and Mo species of the catalyst prepared in ethanol have high dispersibility.

[0065] like Figure 4As shown in the figure, the element distribution diagram of the Fe-Mo / MgAl-LDOs layered metal oxide prepared in ethanol by the method of the present invention is shown. Through EDS surface scanning of the catalyst, it is found that the distribution of Fe and Mo elements in the Fe-Mo / MgAl-LDOs layered metal oxide prepared in ethanol is significantly more uniform, indicating that ethanol can significantly improve the dispersion of metals.

[0066] like Figure 5 As shown in the table below, the water-catalyst corresponds to the Fe-Mo / MgAl-LDOs layered metal oxide prepared in water, and the ethanol-catalyst corresponds to the Fe-Mo / MgAl-LDOs layered metal oxide prepared in Example 1. From the BET results, the adsorption isotherms of the two catalysts are both type II isotherms and have an H1-type hysteresis loop, indicating that the pore size distribution is relatively uniform, which is consistent with the pore size distribution curve results. In the relatively low-pressure region, with the increase of relative pressure, the adsorption amount of N2 slowly increases. At this time, the adsorption of N2 by the pores in the catalyst changes from monolayer adsorption to multilayer adsorption. When P / P0>0.8, the adsorption amount increases rapidly and capillary condensation occurs. Due to the occurrence of capillary condensation, the adsorption curve and the desorption curve do not overlap, thereby generating a hysteresis loop. From the table data, it can be seen that ethanol has a significant effect on the catalyst structure. The Fe-Mo / MgAl-LDOs layered metal oxides prepared in ethanol have a larger specific surface area and pore size, but a smaller pore volume, indicating that the height of the pores in the ethanol-catalyst is smaller, which effectively prevents the SWCNTs from stopping their growth due to "hitting the wall" during the growth process.

[0067] Catalyst <![CDATA[S BET (m 2 g -1 )]]> <![CDATA[Pore volume(cm 3 g -1 )]]> Average pore size (nm) <![CDATA[H2O-Fe1Mo1]]> 239 1.06 17.24 <![CDATA[C2H5OH-Fe1Mo1]]> 256 0.94 30.87

[0068] like Figure 6 As shown, the Fe-Mo / MgAl-LDOs layered metal oxide prepared in Example 1 was used as a catalyst to prepare single-walled carbon nanotubes. Take 50 mg of the prepared Example 1, evenly spread it in an ark and put it into a tube furnace. In an air atmosphere, start from room temperature of 20-25°C and heat it at a rate of 10°C / min to 550°C; introduce H2 for reduction for 1h, with an H2 flow rate of 50mL / min; then turn off H2, and in an Ar atmosphere, heat it at a rate of 5°C / min to 900°C, with an Ar flow rate of 50mL / min; finally, introduce methane for reaction for 30 minutes to prepare single-walled carbon nanotubes. The prepared single-walled carbon nanotubes are attached to the catalyst. In view of the fact that the thermal weight loss range of carbon nanotubes is 400-700 degrees Celsius, thermogravimetric testing is used for analysis. From Figure 6 From the above, the yield of single-walled carbon nanotubes grown on Fe-Mo / MgAl-LDOs layered metal oxides prepared in ethanol is improved. The yield of single-walled carbon nanotubes can be calculated by the formula yield = M SWCNTs / Mcatalyst Calculations show that the mass yield of SWCNTs grown on the ethanol-catalyst reached 39.51%, an 11.5% increase over the yield of SWCNTs grown on the water-catalyst. This is due to the "avalanche" reduction of Mo during the reduction process, which exposes more active sites and significantly increases the yield of single-walled carbon nanotubes.

[0069] The catalysts prepared under different titration conditions were characterized by H2-TPR. The results are as follows: Figure 7 The reduction peak temperatures of the water-catalyst and the ethanol-catalyst are similar, but the intensity of the reduction peak at 612°C for the ethanol-catalyst is enhanced. The reduction peak at 612°C is related to the reduction of Mo species, which means that the content of reduced Mo species in the catalyst increases. This further demonstrates that using ethanol as the titrant can effectively avoid the enrichment of Mo elements in a certain area, improve the dispersion of Mo, and make the Mo species in the catalyst more susceptible to "avalanche" reduction. This not only promotes the improvement of Fe dispersion, but also effectively avoids the appearance of large Mo particles, providing favorable conditions for the growth of SWCNTs with a high degree of graphitization.

[0070] Example 2

[0071] The final calcination temperature in step 6 of Example 1 was changed to 450°C, 500°C, and 550°C, respectively, to prepare different Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional materials. The remaining preparation steps were essentially the same as in Example 1, resulting in the preparation of Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional materials.

[0072] Example 3

[0073] The ratio of Fe to Mo in step 1 of Example 1 was changed to 0.1:0.125, 0.1:0.15, and 0.1:0.2, respectively. The corresponding mass of (NH4)6Mo7O 24 , Fe(NO3)3, Mg(NO3)2, Al(NO3)3. The remaining preparation steps are basically the same as those in Example 1.

[0074] Example 4

[0075] Following the preparation steps of Example 1, the pH value during preparation was changed to control the pH at 9.5±0.05, 10.0±0.05, and 10.5±0.05, and Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional materials were prepared under the same preparation conditions.

[0076] Comparative Example

[0077] Following the preparation steps of Example 1, deionized water was used as the titration solution, that is, deionized water was used as the titration solution, and Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material was prepared under the same preparation conditions.

[0078] like Figure 1 As shown, (a) corresponds to the element distribution diagram of Fe-Mo / MgAl-LDOs layered metal oxide prepared with deionized water as the titration solution, which shows that the Fe and Mo elements are locally unevenly distributed; (b) corresponds to the element distribution diagram of Fe-Mo / MgAl-LDOs layered metal oxide prepared with ethanol as the titration solution, which shows that the Fe and Mo elements are uniformly distributed.

[0079] Example 5 - Application of the ethanol-regulated Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material of the present invention to the catalytic cracking of methane to produce single-walled carbon nanotubes

[0080] The catalytic performance of the ethanol-regulated Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material prepared in Example 1 and the inorganic functional material prepared in the comparative example was tested, with reference to the literature Effect of reduction conditions of Mo-Fe / MgO on the formation of carbon nanotube in catalytic methane decomposition, Journal of Industrial and Engineering Chemistry, 2022, 109: 384-396. The specific method is as follows:

[0081] 50 mg of the prepared inorganic functional materials of Example 1 and the comparative example were respectively taken, evenly spread in an ark and placed in a tubular furnace. In an air atmosphere, the temperature was raised from room temperature of 20-25°C at a rate of 10°C / min to 550°C; H2 was introduced for reduction for 1 hour at a H2 flow rate of 50 mL / min; then H2 was turned off, and the temperature was raised at a rate of 5°C / min to 900°C under an Ar atmosphere at a flow rate of 50 mL / min; finally, methane was introduced for reaction for 30 minutes to prepare single-walled carbon nanotubes.

[0082] like Figure 8 As shown, single-walled carbon nanotubes were successfully prepared using the catalyst prepared in Example 1 of the present invention. Figure 9These are Raman test results for single-walled carbon nanotubes prepared using the catalysts prepared in Example 1 and the comparative example of the present invention, wherein (a) corresponds to the single-walled carbon nanotubes prepared at 900°C for the comparative example, and (b) corresponds to the single-walled carbon nanotubes prepared at 900°C for Example 1. It can be seen that the application of the Fe-Mo / MgAl-LDOs layered metal oxide inorganic functional material of the present invention in the preparation of single-walled carbon nanotubes by catalytic cracking of methane successfully achieves the preparation of single-walled carbon nanotubes; and 0.08<0.11, indicating that the single-walled carbon nanotubes prepared using the material of the present invention as a catalyst have a higher degree of graphitization and a lower defect density.

[0083] According to the present invention, by adjusting the process parameters in the examples, the layered metal oxide can be prepared, and after testing, the performance is basically consistent with that of the present invention. The above description of the present invention is illustrative. It should be noted that any simple variation, modification, or equivalent substitution that can be made by a person skilled in the art without inventive effort falls within the scope of protection of the present invention without departing from the core of the present invention.

Claims

1. Ethanol-regulated layered metal compounds, characterized in that: The layered metal oxides regulated by ethanol are Fe-Mo / MgAl-LDOs layered metal oxides, with the molar ratio of the four elements Fe:Mo:Mg:Al=x:y:2:1, x and y are between 0.025-0.5, and the specific surface area is 220-260m 2 / g, pore volume 0.8-1.2cm 3 / g, with an average pore size of 15-32nm, follow the steps below: Step 1, stirring ethanol as a titration solution at 60-80° C., and when the temperature is stabilized at 60-80° C., adjusting the pH of the ethanol titration solution to 8.0-11.0 with alkaline solution; Step 2, adding the soluble metal salt solution and the alkali solution dropwise to the mixed solution obtained in step 1 while stirring, maintaining the temperature at 60-80° C., and controlling the pH at 8.0-11.0; Step 3: After the addition is completed, continue stirring and aging for 1-15 hours, then stop stirring, and age the obtained precipitate in a 40-80°C water bath for 1-15 hours, filter, wash, and dry the precipitate to obtain a precursor; Step 4: Grind the precursor obtained in step 3 and calcine it. In an air atmosphere, start from room temperature 20-25°C, heat it at a rate of 1-5°C / min to 300-450°C, and keep it warm for 1-5 hours; then heat it at a rate of 1-5°C / min to 500-900°C, keep it warm for 1-5 hours, and finally cool it to room temperature 20-25°C with the furnace.

2. The ethanol-regulated layered metal compound according to claim 1, characterized in that: x and y are 0.025-0.2, preferably 0.1-0.2; the specific surface area is 230-260m 2 / g; pore volume is 0.9-1.1cm 3 / g; the average pore size is 17-31nm.

3. The method for preparing the ethanol-regulated layered metal compound according to claim 1, wherein: Follow the steps below: Step 1, stirring ethanol as a titration solution at 60-80° C., and when the temperature is stabilized at 60-80° C., adjusting the pH of the ethanol titration solution to 8.0-11.0 with alkaline solution; Step 2, adding the soluble metal salt solution and the alkali solution dropwise to the mixed solution obtained in step 1 while stirring, maintaining the temperature at 60-80° C., and controlling the pH at 8.0-11.0; Step 3: After the addition is completed, continue stirring and aging for 1-15 hours, then stop stirring, and age the obtained precipitate in a 40-80°C water bath for 1-15 hours, filter, wash, and dry the precipitate to obtain a precursor; Step 4: Grind the precursor obtained in step 3 and calcine it. In an air atmosphere, start from room temperature 20-25°C, heat it at a rate of 1-5°C / min to 300-450°C, and keep it warm for 1-5 hours; then heat it at a rate of 1-5°C / min to 500-900°C, keep it warm for 1-5 hours, and finally cool it to room temperature 20-25°C with the furnace.

4. The method for preparing the ethanol-regulated layered metal compound according to claim 3, wherein: In step 1, the alkali solution is an aqueous solution of sodium hydroxide and sodium carbonate. For example, a predetermined amount of sodium hydroxide and sodium carbonate is weighed and dissolved in deionized water; the concentration of sodium hydroxide is controlled at 0.10-0.30 mol / L, and the concentration of sodium carbonate is controlled at 0.6-1.0 mol / L; 20-50 mL of anhydrous ethanol is measured as the titration solution, the stirring speed is 100-300 revolutions per minute, and the pH is adjusted to 9.0-11.

0.

5. The method for preparing ethanol-regulated layered metal compounds according to claim 3, wherein: In step 2, the dripping speed of the soluble metal salt solution should be controlled within a range of 1 drop per 2 seconds to 2 drops per 1 second; the dripping speed of the alkali solution should be controlled according to the pH change of the reaction system during the entire reaction process; The pH is controlled to 9.0-11.0; the stirring speed is 100-300 revolutions per minute.

6. The method for preparing ethanol-regulated layered metal compounds according to claim 3, wherein: In step 2, the alkali solution is an aqueous solution of sodium hydroxide and sodium carbonate, such as weighing a predetermined amount of sodium hydroxide and sodium carbonate, adding deionized water to dissolve; the concentration of sodium hydroxide is controlled at 0.10-0.30 mol / L, and the concentration of sodium carbonate is controlled at 0.6-1.0 mol / L; the corresponding soluble metal salts are weighed according to the ratio of the four metal elements, adding deionized water to dissolve to form a soluble metal salt solution, and the total metal ion concentration is controlled at 0.20-0.50 mol / L; the soluble metal salts are ammonium molybdate, ferric nitrate, magnesium nitrate, and aluminum nitrate.

7. The method for preparing ethanol-regulated layered metal compounds according to claim 3, wherein: In step 3, the stirring speed is 100-300 revolutions per minute, the stirring aging time is 10-15 hours, the aging temperature is 60-80° C., the aging time is 10-15 hours, and the drying temperature is 60-120° C., and the drying time is 8-24 hours.

8. The method for preparing ethanol-regulated layered metal compounds according to claim 3, wherein: In step 4, starting from room temperature of 20-25°C in an air atmosphere, the temperature is raised at a rate of 1-2°C / min to 400-450°C, and kept warm for 3-4 hours; then the temperature is raised at a rate of 1-2°C / min to 600-700°C, kept warm for 2-3 hours, and finally cooled to room temperature of 20-25°C with the furnace; a muffle furnace is selected for calcination.

9. Use of the ethanol-regulated layered metal compound in the preparation of single-walled carbon nanotubes by catalytic cracking of methane as claimed in claim 1 or 2, characterized in that: H2 is needed to reduce the ethanol-regulated layered metal oxide, and an inert protective gas is introduced as a protective atmosphere during the heating process.

10. The use according to claim 9, characterized in that The specific steps are as follows: Step 1: Weigh a predetermined amount of ethanol to regulate the layered metal oxide as a catalyst in an ark, and heat the ark to a reduction temperature in an inert protective atmosphere in a tube furnace at a flow rate of 50-80 mL / min; the reduction temperature is 500-600 degrees Celsius; Step 2, introducing H2 for reduction, such as for 30-60 min, with a H2 flow rate of 30-60 mL / min; Step 3: Turn off H2 and raise the temperature to the reaction temperature in an inert protective atmosphere at a flow rate of 50-80 mL / min; the reaction temperature is 800-1000 degrees Celsius; Step 4: adding methane for reaction, with a reaction time of 30-60 min and a methane flow rate of 10-30 mL / min; Step 5: Turn off the methane and cool the furnace under an inert protective gas atmosphere to obtain single-walled carbon nanotubes.

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