Amorphous composite metal oxide hollow nanospheres and preparation method and application thereof

Abstract

This invention belongs to the field of catalytic materials technology, and relates to a hollow nanosphere material, its preparation method, and its applications, particularly an amorphous composite metal oxide hollow nanosphere material, its preparation method, and its application in the catalytic cracking of low-carbon hydrocarbons to prepare nano-carbon materials. The amorphous composite metal oxide hollow nanosphere material prepared by this invention exhibits extremely high catalytic activity and nano-carbon material yield in the process of catalytic cracking of low-carbon hydrocarbons to synthesize nano-carbon materials. The hollow nanosphere structure increases the contact area between reactant molecules and the catalyst, reduces the transport distance of reactant molecules to the active center, and the unique internal cavity provides ample space for the growth of nano-carbon materials, avoiding the blockage of the catalyst's internal channels by the synthesized nano-carbon materials, thus preventing the isolation of reactant molecules from the active center.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, and relates to a hollow nanosphere material, its preparation method and application, especially to an amorphous composite metal oxide hollow nanosphere material, its preparation method and its application in the catalytic cracking of low-carbon hydrocarbons to prepare nano-carbon materials. Background Technology

[0002] Carbon nanomaterials have wide applications in the new energy field due to their excellent electrical and thermal conductivity. Catalytic cracking is the main method for preparing carbon nanomaterials. This method decomposes carbon source gas into carbon and hydrogen atoms under the action of a catalyst. The carbon atoms are deposited on the catalyst surface and self-assemble to form carbon nanomaterials. In this method, the catalyst is the substrate for the growth of carbon nanomaterials. The grown carbon nanomaterials are prone to clogging the catalyst pores, preventing the contact between the active centers inside the catalyst particles and the reactants, resulting in catalyst deactivation. Existing methods mainly improve this problem by adjusting the specific surface area and pore structure of the catalyst support. However, the growth space provided by the mesoporous channels of the catalyst particles is limited, and many active centers inside the catalyst particles cannot participate in the reaction.

[0003] Therefore, there is an urgent need to develop a catalyst with higher activity to achieve the catalytic cracking of low-carbon hydrocarbons to synthesize nano-carbon materials while improving the yield of nano-carbon materials. Summary of the Invention

[0004] To address the aforementioned issues, hollow spherical catalysts can be designed to provide sufficient growth space for carbon nanomaterials. Hollow nanospheres possess unique internal cavity structures, low density, and high specific surface area, making them promising candidates for catalysis. In the catalytic cracking synthesis of carbon nanomaterials, the shell of the hollow nanospheres exhibits a well-developed pore structure, ensuring the entry of reactant molecules. The unique internal cavity provides ample space for the growth of carbon nanomaterials, preventing the synthesized nanospheres from clogging the catalyst's internal pores and isolating reactant molecules from the active sites. Furthermore, the hollow nanosphere structure increases the contact area between reactant molecules and the catalyst, reducing the transport distance from reactant molecules to the active sites, thus enhancing catalytic activity. Therefore, this invention proposes an amorphous composite metal oxide hollow nanosphere material. The prepared hollow nanosphere material exhibits high catalytic activity and high yield of carbon nanomaterials during the catalytic cracking of low-carbon hydrocarbons.

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing an amorphous composite metal oxide hollow nanosphere material, its preparation method, and its application, so as to improve the catalytic activity for the synthesis of nano-carbon materials from the catalytic cracking of low-carbon hydrocarbons, thereby increasing the yield of nano-carbon materials.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides an amorphous composite metal oxide hollow nanosphere material, wherein the material is a composite metal oxide of Fe2O3 and Al2O3, wherein the molar ratio of Al to Fe is (0.1-5):1, and it has a hollow spherical structure with a diameter of 200-300 nm and a wall thickness of 20-40 nm.

[0008] This invention also provides a method for preparing the above-mentioned amorphous composite metal oxide hollow nanosphere material, which mainly includes the following steps:

[0009] (1) Dissolve the carbon source in deionized water to obtain a carbon source solution. After hydrothermal reaction, the carbon source solution is centrifuged, washed and dried to obtain a carbon ball template.

[0010] (2) Dissolve the weak acid salt in deionized water to obtain a weak acid salt solution, prepare a pH buffer solution using the corresponding weak acid, add carbon ball template, iron source and aluminum source and stir evenly, and then perform ultrasonic crushing until the mixture is evenly mixed to obtain a mixed solution (preferably ultrasonic crushing treatment for 10 to 30 min).

[0011] (3) The mixed solution is kept at 60-80℃ for 1-3 hours. After the heat treatment is completed, the solution is centrifuged, washed and dried to obtain the precursor. The precursor is calcined in air to obtain the amorphous composite metal oxide hollow nanospheres.

[0012] Furthermore, the carbon source is one or more combinations of glucose, fructose, sucrose, maltose, starch, and citric acid, preferably glucose.

[0013] Furthermore, the concentration of the carbon source solution is 0.1–5 mol / L, preferably 0.3–1 mol / L.

[0014] Furthermore, the hydrothermal reaction is carried out in a sealed reactor at a temperature of 170–190°C for 1–5 hours, preferably at 180°C for 3–4 hours.

[0015] Furthermore, the centrifugation operation is carried out in a centrifuge with a speed of 9000-11000 rpm and a centrifugation time of 20-40 min.

[0016] Furthermore, in both steps (1) and (3), deionized water and / or anhydrous ethanol are used for washing, and the number of washing cycles is 3 to 5.

[0017] Furthermore, the drying temperature is 70–90°C, and the drying time is 6–24 hours, preferably 12 hours at 80°C.

[0018] Furthermore, the weak acid salt is one or more of sodium citrate, sodium acetate, sodium oxalate, ammonium acetate, and ammonium formate, and the concentration of the weak acid salt solution is 0.1 to 1 mol / L (preferably 0.4 mol / L); the corresponding weak acid is one or more of citric acid, acetic acid, oxalic acid, and formic acid, and the pH of the pH buffer solution is 4.0-4.8.

[0019] Furthermore, the concentration of the weak acid salt solution is 0.1–1 mol / L.

[0020] Furthermore, the weak acid is one or more of citric acid, acetic acid, oxalic acid, and formic acid.

[0021] Furthermore, the pH value of the pH buffer solution is 3 to 5, preferably 4.2 to 4.6.

[0022] Furthermore, the iron source is one or more of ferric nitrate, ferric sulfate, ferric chloride, ferrous sulfate, and ferric acetate, and the concentration of the iron source in the mixed solution in step (2) is 0.1–100 mmol / L, preferably 4–10 mmol / L; and / or

[0023] The aluminum source is one or more of aluminum nitrate, aluminum sulfate, aluminum chloride, and alum. The molar ratio of aluminum ions to iron ions in the mixed solution in step (2) is 0.1 to 5:1, preferably 2 to 3:1.

[0024] Furthermore, in the mixed solution of step (2), the concentration of carbon sphere template is 0.1-5 g / L, preferably 0.8 g / L;

[0025] Furthermore, the precursor calcination process is carried out in a muffle furnace or a tube furnace, the calcination temperature of the precursor is 400-600℃, the calcination time is 1-5h, preferably heated to 500℃ at a heating rate of 5℃ / min and then calcined for 3h.

[0026] This invention also provides the application of the above-mentioned amorphous composite metal oxide hollow nanosphere material in the preparation of nanocarbon materials by catalytic cracking of low-carbon hydrocarbons.

[0027] Furthermore, the specific operation of the application is as follows:

[0028] (1-1) The above-mentioned amorphous composite metal oxide hollow nanosphere material is added into a fluidized bed reactor, and gas is introduced to carry out the catalyst reduction process;

[0029] (2-2) After the reduction is completed, a reaction gas is introduced to carry out the synthesis reaction of nano-carbon materials. The reaction gas is a mixture of carbon source gas and inert gas, and the volume ratio of carbon source gas to inert gas is 0.1 to 10:1 (preferably 1:1).

[0030] (3-3) After the reaction is complete, the nano-carbon material is collected, washed with alkali, acid, water and / or anhydrous ethanol, and dried to obtain pure nano-carbon material.

[0031] Furthermore, the gas used in the reduction process is a mixture of hydrogen and an inert gas, with a volume ratio of hydrogen to inert gas of 0.1 to 2:1 (preferably 1:1), and the flow rate of the mixture during the reduction process is 20 to 40 cm⁻¹. 3 / s, the temperature of the reduction process is 600~800℃, the reduction time is 10~60min, preferably at 750℃ for 30min.

[0032] Furthermore, the inert gas is one of nitrogen, argon, and helium.

[0033] Furthermore, the carbon source gas is one or more of methane, ethane, ethylene, propane, propylene, and butane.

[0034] Furthermore, the temperature of the synthesis reaction is 650–1000°C, and the reaction time is 40–180 min, preferably 90 min at 750°C.

[0035] Furthermore, the flow rate of the mixed gas in the synthesis reaction is 20–40 cm⁻¹. 3 / s.

[0036] Furthermore, the alkaline solution used in the alkaline washing process is a sodium hydroxide or potassium hydroxide solution with a concentration of 0.5–3 mol / L, an alkaline washing temperature of 65–85°C, and an alkaline washing time of 4–24 h. Preferably, a 2 mol / L potassium hydroxide solution is used for alkaline washing at 80°C for 12 h.

[0037] Furthermore, the acid used in the pickling process is one or more of hydrochloric acid, nitric acid, and sulfuric acid, with an acid solution concentration of 0.5–3 mol / L, a pickling temperature of 65–85°C, and a pickling time of 4–24 h. Preferably, 2 mol / L hydrochloric acid is used for pickling at 80°C for 12 h.

[0038] Furthermore, the product is washed with deionized water and / or anhydrous ethanol, and the washing process is repeated 3 to 5 times.

[0039] Furthermore, the drying temperature in step (3-3) is 70-90°C, and the drying time is 6-24 hours, preferably 12 hours at 80°C.

[0040] The nano-carbon materials prepared in the above application process are formed by rolling up several or dozens of carbon atom layers. The microstructure is a hollow tubular structure with an outer diameter of 10-40 nm and a tube wall consisting of several or dozens of carbon atom layers with a length of several micrometers.

[0041] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0042] (1) The amorphous composite metal oxide hollow nanosphere material prepared by the present invention has extremely high catalytic activity and nanocarbon material yield in the process of catalytic cracking of low carbon hydrocarbons to synthesize nanocarbon materials. The hollow nanosphere structure increases the contact area between reactant molecules and catalyst, reduces the transport distance of reactant molecules to active center, and the unique internal cavity provides sufficient space for the growth of nanocarbon materials, avoiding the blockage of internal channels of catalyst by synthesized nanocarbon materials, which would cause the reactant molecules to be isolated from the active center.

[0043] (2) This invention controls the size of the carbon template by controlling the concentration of the carbon source solution and the hydrothermal synthesis time, thereby controlling the size of the internal cavity of the amorphous composite metal oxide hollow nanosphere material. The shell thickness of the material is controlled by controlling the concentrations of the iron and aluminum sources in the solution. This invention achieves regulation of the catalytic performance and yield of the nano-carbon material by controlling the size of the internal cavity and the shell thickness of the material. Attached Figure Description

[0044] Figure 1 The image shows a SEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 1.

[0045] Figure 2 This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 1.

[0046] Figure 3 The elemental distribution diagram is shown for the amorphous metal oxide hollow nanosphere material prepared in Example 1.

[0047] Figure 4 The XRD pattern of the amorphous metal oxide hollow nanosphere material prepared in Example 1.

[0048] Figure 5 This is a SEM image of the nano-carbon material synthesized in Example 1.

[0049] Figure 6 This is a TEM image of the carbon nanomaterial synthesized in Example 1.

[0050] Figure 7 This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 2.

[0051] Figure 8 This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 3.

[0052] Figure 9 This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 4.

[0053] Figure 10 This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 5. Detailed Implementation

[0054] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0055] In this invention, room temperature refers to 25°C.

[0056] In the following examples, during the hydrothermal reaction, the volume of the glucose aqueous solution was 80% of the reactor volume; the pH of the pH buffer solution was 4.5-4.8.

[0057] The resulting carbon nanomaterials are formed by rolling up several or dozens of carbon atom layers. The microstructure is a hollow tubular structure with an outer diameter of 10–40 nm and a tube wall consisting of several or dozens of carbon atom layers with a length of several micrometers.

[0058] Unless otherwise specified, all organic solvents used were purchased analytical grade solvents.

[0059] Example 1: Synthesis of amorphous composite metal oxide hollow nanospheres, comprising the following steps:

[0060] (1) A 0.6 mol / L glucose aqueous solution was placed in a reaction vessel, and the heating temperature was set to 180℃. The hydrothermal reaction was carried out for 3.5 h. After the reaction was completed, the solution was naturally cooled to room temperature. The solution after the reaction was centrifuged and washed. The centrifuge speed was 1000 r / min and the centrifugation time was 30 min. The precipitate was washed alternately with deionized water and ethanol for a total of 4 times. The precipitate was dried at 80℃ for 12 h to obtain carbon sphere templates.

[0061] (2) Dissolve 7.56g of ammonium formate in 300mL of deionized water, and add 1.02g of formic acid to prepare a pH buffer solution. Add 0.24g of carbon sphere template, 0.72g of aluminum sulfate, and 0.43g of ferric nitrate to the pH buffer solution and stir until homogeneous. Sonicate the mixture for 15min to disperse the carbon spheres evenly in the solution. Incubate at 70℃ for 2.5h with continuous stirring. After incubation, centrifuge and wash the precipitate at 1000r / min for 30min. Wash the precipitate three times with deionized water. Dry the precipitate at 80℃ for 12h to obtain the precursor. Place the precursor in a muffle furnace and heat to 500℃ at a heating rate of 5℃ / min. Calcinate for 3h and then allow to cool naturally to room temperature to obtain amorphous composite metal oxide hollow nanospheres with a bulk density of 450kg / m³. 3 The specific surface area is 310 m². 2 / g.

[0062] Figure 1The image shows a SEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 1. Figure 2 This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 1. Figure 1 , Figure 2 As shown, the diameter of the amorphous metal oxide hollow nanosphere material is approximately 180–200 nm, the inner diameter is approximately 150 nm, and the shell thickness is approximately 30 nm.

[0063] Figure 3 The elemental distribution diagram is shown for the amorphous metal oxide hollow nanosphere material prepared in Example 1. Figure 3 As shown, Fe and Al metal elements are uniformly distributed in the hollow nanosphere material.

[0064] Figure 4 The XRD pattern is shown for the amorphous metal oxide hollow nanosphere material prepared in Example 1. Figure 4 As shown, the XRD spectrum of the material is a curve with a gradual change in intensity, indicating that it is amorphous. From the perspective of the Scherrer equation, this curve can be regarded as the result of the crystal diffraction peaks becoming extremely broad and overlapping as the grain size decreases to an extreme degree. This indicates that the metal oxide in the material exists in the form of microcrystals, exhibiting a structure of short-range order and long-range disorder. This structure promotes the uniform dispersion of the metal.

[0065] The steps for synthesizing nano-carbon materials using amorphous metal oxide hollow nanospheres as catalysts are as follows:

[0066] Amorphous metal oxide hollow nanospheres were added to a fluidized bed reactor (40 mm × 1400 mm) at a rate of 1 g. The reactor was heated to 750 °C at a rate of 10 °C / min under a nitrogen atmosphere. Then, hydrogen and nitrogen were introduced at a rate of 1 L / min for catalyst reduction for 30 min. After reduction, the reactor was further heated at 750 °C with ethane and nitrogen at a rate of 1 L / min for 90 min to synthesize carbon nanomaterials. After the reaction, the mixture was naturally cooled to room temperature under nitrogen protection. The carbon nanomaterials were collected, washed with 2 mol / L potassium hydroxide solution at 80 °C for 12 h, and then acid-washed with 2 mol / L hydrochloric acid at 80 °C for 12 h. The carbon nanomaterials were filtered and washed four times alternately with deionized water and ethanol, and then dried at 80 °C for 12 h to obtain pure carbon nanomaterials. The yield of the carbon nanomaterials was 49.3 g. CNT / g cat (That is, the ratio of the mass of nano-carbon materials to the mass of catalyst, the same below, will not be repeated).

[0067] Figure 5 This is a SEM image of the carbon nanomaterial synthesized in Example 1. Figure 5As shown, the synthesized nano-carbon material has a high aspect ratio fibrous structure and an overall interwoven network structure with almost no trace of amorphous carbon particles, indicating high purity.

[0068] Figure 6 This is a TEM image of the carbon nanomaterial synthesized in Example 1. Figure 6 As shown, the synthesized carbon nanomaterials have a hollow tubular structure with an outer diameter of approximately 15–25 nm.

[0069] Example 2: Synthesis of amorphous composite metal oxide hollow nanospheres, comprising the following steps:

[0070] (1) A 1.0 mol / L glucose aqueous solution was placed in a reaction vessel, and the heating temperature was set to 180℃ for hydrothermal reaction for 4 hours. After the reaction, the solution was allowed to cool naturally to room temperature. The reacted solution was centrifuged and washed at 1000 r / min for 30 min. The precipitate was washed alternately with deionized water and ethanol for a total of 4 times. The precipitate was dried at 80℃ for 12 hours to obtain carbon sphere templates.

[0071] (2) Dissolve 7.56 g of ammonium formate in 300 mL of deionized water, and add 1.02 g of formic acid to prepare a pH buffer solution. Add 0.24 g of carbon sphere template, 0.72 g of aluminum sulfate, and 0.43 g of ferric nitrate to the pH buffer solution and stir until homogeneous. Sonicate the mixture for 15 min to disperse the carbon spheres evenly in the solution. Keep it at 70 °C for 2.5 h with continuous stirring. After the incubation period, centrifuge and wash the precipitate at 1000 r / min for 30 min. Wash the precipitate three times with deionized water. Dry the precipitate at 80 °C for 12 h to obtain the precursor. Place the precursor in a muffle furnace and heat it to 500 °C at a heating rate of 5 °C / min. Calcinate for 3 h and then cool naturally to room temperature to obtain amorphous composite metal oxide hollow nanosphere material.

[0072] Figure 7 This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 2. Figure 7 As shown, the diameter of the amorphous metal oxide hollow nanosphere material is approximately 300 nm, the inner diameter is approximately 270 nm, and the shell thickness is approximately 20 nm.

[0073] The steps for synthesizing nano-carbon materials using amorphous metal oxide hollow nanospheres as catalysts are as follows:

[0074] Amorphous metal oxide hollow nanospheres were added to a fluidized bed reactor (40 mm × 1400 mm) at a rate of 1 g. The reactor was heated to 750 °C at a rate of 10 °C / min under a nitrogen atmosphere. Hydrogen and nitrogen were introduced at a rate of 1 L / min for catalyst reduction for 30 min. After reduction, the reactor was further heated at 750 °C with 1 L / min of ethane and 1 L / min of nitrogen for the synthesis of carbon nanomaterials for 90 min. After the reaction, the mixture was naturally cooled to room temperature under nitrogen protection. The carbon nanomaterials were collected, washed with 2 mol / L potassium hydroxide solution at 80 °C for 12 h, and then washed with 2 mol / L hydrochloric acid at 80 °C for 12 h. The carbon nanomaterials were filtered and washed four times alternately with deionized water and ethanol, and then dried at 80 °C for 12 h to obtain pure carbon nanomaterials. The yield of the carbon nanomaterials was 56.7 g. CNT / g cat .

[0075] Example 3: Synthesis of amorphous composite metal oxide hollow nanospheres, comprising the following steps:

[0076] (1) A 0.3 mol / L glucose aqueous solution was placed in a reaction vessel, and the heating temperature was set to 180℃ for a hydrothermal reaction for 3 hours. After the reaction, the solution was allowed to cool naturally to room temperature. The reacted solution was centrifuged and washed at 1000 r / min for 30 min. The precipitate was washed alternately with deionized water and ethanol a total of 4 times. The precipitate was dried at 80℃ for 12 hours to obtain carbon sphere templates.

[0077] (2) Dissolve 7.56 g of ammonium formate in 300 mL of deionized water, and add 1.02 g of formic acid to prepare a pH buffer solution. Add 0.24 g of carbon sphere template, 0.72 g of aluminum sulfate, and 0.43 g of ferric nitrate to the pH buffer solution and stir until homogeneous. Sonicate the mixture for 15 min to disperse the carbon spheres evenly in the solution. Keep it at 70 °C for 2.5 h with continuous stirring. After the incubation period, centrifuge and wash the precipitate at 1000 r / min for 30 min. Wash the precipitate three times with deionized water. Dry the precipitate at 80 °C for 12 h to obtain the precursor. Place the precursor in a muffle furnace and heat it to 500 °C at a heating rate of 5 °C / min. Calcinate for 3 h and then cool naturally to room temperature to obtain amorphous composite metal oxide hollow nanosphere material.

[0078] Figure 8 This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 3. Figure 8 As shown, the diameter of the amorphous metal oxide hollow nanosphere material is approximately 200 nm, the inner diameter is approximately 120 nm, and the shell thickness is approximately 40 nm.

[0079] The steps for synthesizing nano-carbon materials using amorphous metal oxide hollow nanospheres as catalysts are as follows:

[0080] Amorphous metal oxide hollow nanospheres were added to a fluidized bed reactor (40 mm × 1400 mm) at a rate of 1 g. The reactor was heated to 750 °C at a rate of 10 °C / min under a nitrogen atmosphere. Hydrogen and nitrogen were introduced at a rate of 1 L / min for catalyst reduction for 30 min. After reduction, the reaction proceeded at 750 °C with ethane and nitrogen at a rate of 1 L / min for 90 min. After the reaction, the mixture was allowed to cool naturally to room temperature under nitrogen protection. The nanospheres were collected, washed with 2 mol / L potassium hydroxide solution at 80 °C for 12 h, and then acid-washed with 2 mol / L hydrochloric acid at 80 °C for 12 h. The nanospheres were filtered and washed four times alternately with deionized water and ethanol, and then dried at 80 °C for 12 h to obtain pure nanospheres. The yield of the nanospheres was 28.4 g. CNT / g cat .

[0081] Example 4: Synthesis of amorphous composite metal oxide hollow nanospheres, comprising the following steps:

[0082] (1) A 0.6 mol / L glucose aqueous solution was placed in a reaction vessel, and the heating temperature was set to 180℃ for a hydrothermal reaction for 3.5 h. After the reaction, the solution was allowed to cool naturally to room temperature. The reacted solution was centrifuged and washed at 1000 r / min for 30 min. The precipitate was washed alternately with deionized water and ethanol four times. The precipitate was dried at 80℃ for 12 h to obtain carbon sphere templates.

[0083] (2) Dissolve 7.56 g of ammonium formate in 300 mL of deionized water, and add 1.02 g of formic acid to prepare a pH buffer solution. Add 0.24 g of carbon sphere template, 1.08 g of aluminum sulfate, and 0.65 g of ferric nitrate to the pH buffer solution and stir until homogeneous. Sonicate the mixture for 15 min to disperse the carbon spheres evenly in the solution. Keep it at 70 °C for 2.5 h with continuous stirring. After the incubation period, centrifuge and wash the precipitate at 1000 r / min for 30 min. Wash the precipitate three times with deionized water. Dry the precipitate at 80 °C for 12 h to obtain the precursor. Place the precursor in a muffle furnace and heat it to 500 °C at a heating rate of 5 °C / min. Calcinate for 3 h and then cool naturally to room temperature to obtain amorphous composite metal oxide hollow nanosphere material.

[0084] Figure 9This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 4. Figure 4 As shown, the diameter of the amorphous metal oxide hollow nanosphere material is approximately 240 nm, the inner diameter is approximately 150 nm, and the shell thickness is approximately 40 nm.

[0085] The steps for synthesizing nano-carbon materials using amorphous metal oxide hollow nanospheres as catalysts are as follows:

[0086] Amorphous metal oxide hollow nanospheres were added to a fluidized bed reactor (40 mm × 1400 mm) at a rate of 1 g. The reactor was heated to 750 °C at a rate of 10 °C / min under a nitrogen atmosphere. Hydrogen and nitrogen were introduced at a rate of 1 L / min for catalyst reduction for 30 min. After reduction, the reactor was further heated at 750 °C with 1 L / min of ethane and 1 L / min of nitrogen for the synthesis of carbon nanomaterials for 90 min. After the reaction, the mixture was naturally cooled to room temperature under nitrogen protection. The carbon nanomaterials were collected, washed with 2 mol / L potassium hydroxide solution at 80 °C for 12 h, and then washed with 2 mol / L hydrochloric acid at 80 °C for 12 h. The carbon nanomaterials were filtered and washed four times alternately with deionized water and ethanol, and then dried at 80 °C for 12 h to obtain pure carbon nanomaterials. The yield of the carbon nanomaterials was 33.5 g. CNT / g cat .

[0087] Example 5: Synthesis of amorphous composite metal oxide hollow nanospheres, comprising the following steps:

[0088] (1) A 0.6 mol / L glucose aqueous solution was placed in a reaction vessel, and the heating temperature was set to 180℃ for a hydrothermal reaction for 3.5 h. After the reaction, the solution was allowed to cool naturally to room temperature. The reacted solution was centrifuged and washed at 1000 r / min for 30 min. The precipitate was washed alternately with deionized water and ethanol four times. The precipitate was dried at 80℃ for 12 h to obtain carbon sphere templates.

[0089] (2) Dissolve 7.56 g of ammonium formate in 300 mL of deionized water, and add 1.02 g of formic acid to prepare a pH buffer solution. Add 0.24 g of carbon sphere template, 0.54 g of aluminum sulfate, and 0.32 g of ferric nitrate to the pH buffer solution and stir until homogeneous. Sonicate the mixture for 15 min to disperse the carbon spheres evenly in the solution. Keep it at 70 °C for 2.5 h with continuous stirring. After the incubation period, centrifuge and wash the precipitate at 1000 r / min for 30 min. Wash the precipitate three times with deionized water. Dry the precipitate at 80 °C for 12 h to obtain the precursor. Place the precursor in a muffle furnace and heat it to 500 °C at a heating rate of 5 °C / min. Calcinate for 3 h and then cool naturally to room temperature to obtain amorphous composite metal oxide hollow nanosphere material.

[0090] Figure 10 This is a TEM image of the amorphous metal oxide hollow nanosphere material prepared in Example 5. Figure 5 As shown, the diameter of the amorphous metal oxide hollow nanosphere material is approximately 200 nm, the inner diameter is approximately 150 nm, and the shell thickness is approximately 20 nm.

[0091] The steps for synthesizing nano-carbon materials using amorphous metal oxide hollow nanospheres as catalysts are as follows:

[0092] Amorphous metal oxide hollow nanospheres were added to a fluidized bed reactor (40 mm × 1400 mm) at a rate of 1 g. The reactor was heated to 750 °C at a rate of 10 °C / min under a nitrogen atmosphere. Hydrogen and nitrogen were introduced at a rate of 1 L / min for catalyst reduction for 30 min. After reduction, the reactor was further heated at 750 °C with 1 L / min of ethane and 1 L / min of nitrogen for the synthesis of carbon nanomaterials for 90 min. After the reaction, the mixture was naturally cooled to room temperature under nitrogen protection. The carbon nanomaterials were collected, washed with 2 mol / L potassium hydroxide solution at 80 °C for 12 h, and then washed with 2 mol / L hydrochloric acid at 80 °C for 12 h. The carbon nanomaterials were filtered and washed four times alternately with deionized water and ethanol, and then dried at 80 °C for 12 h to obtain pure carbon nanomaterials. The yield of the carbon nanomaterials was 44.9 g. CNT / g cat .

[0093] Experiments were conducted to investigate the effects of aeration rate and reaction time on the reaction products during the synthesis reaction. Single-variable experiments revealed that: when the aeration rate increased or the reaction time decreased, the carbon nanomaterials in the reaction product appeared visibly whitish, indicating a shortening of the carbon nanomaterial length and reduced uniformity. This was attributed to the interruption of the reaction due to increased aeration rate or shortened reaction time, leading to incomplete carbon nanomaterial growth. When the aeration rate decreased or the reaction time increased, the carbon nanomaterials in the reaction product appeared flocculent, indicating excessive cross-linking of the carbon nanomaterials and reduced uniformity. This was attributed to excessive reaction due to decreased aeration rate or excessively long reaction time, causing carbon atoms to accumulate on the catalyst surface and undergo excessive cross-linking after branching growth. Therefore, the optimal aeration rate was determined to be 20–40 cm⁻¹. 3 The optimal synthesis reaction temperature is 650–1000℃, and the reaction time is 40–180 min.

[0094] Comparative Example 1:

[0095] 7.56 g of ammonium formate was dissolved in 300 mL of deionized water, and 1.02 g of formic acid was added to prepare a pH buffer solution. 0.72 g of aluminum sulfate and 0.43 g of ferric nitrate were added to the pH buffer solution and stirred until homogeneous. The mixture was incubated at 70 °C for 2.5 h with continuous stirring. After incubation, the solution was centrifuged and washed at 1000 rpm for 30 min. The precipitate was washed three times with deionized water. The precipitate was dried at 80 °C for 12 h to obtain the precursor. The precursor was placed in a muffle furnace and heated to 500 °C at a heating rate of 5 °C / min for 3 h. After calcination, it was allowed to cool naturally to room temperature to obtain the amorphous composite metal oxide material.

[0096] Amorphous metal oxide material was added to a fluidized bed reactor (40 mm × 1400 mm) at a rate of 1 g. The reactor was heated to 750 °C at a rate of 10 °C / min under a nitrogen atmosphere. Hydrogen and nitrogen were introduced at a rate of 1 L / min for catalyst reduction for 30 min. After reduction, the reactor was further heated at 750 °C with ethane and nitrogen introduced at a rate of 1 L / min for 90 min. After the reaction, the mixture was allowed to cool naturally to room temperature under nitrogen protection. The nanocarbon material was collected, washed with 2 mol / L potassium hydroxide solution at 80 °C for 12 h, and then acid-washed with 2 mol / L hydrochloric acid at 80 °C for 12 h. The nanocarbon material was filtered and washed four times alternately with deionized water and ethanol, and then dried at 80 °C for 12 h to obtain pure nanocarbon material. The yield of the nanocarbon material was 14.5 g. CNT / g cat .

Claims

1. An amorphous composite metal oxide hollow nanosphere material, wherein the amorphous composite metal oxide hollow nanosphere material is a composite metal oxide of Fe2O3 and Al2O3, wherein the molar ratio of Al to Fe is (0.1~5):1, and it has a hollow spherical structure with a diameter of 200~300 nm and a wall thickness of 20~40 nm; the amorphous composite metal oxide hollow nanosphere material is a nanosphere shell formed by microcrystalline Fe2O3 and microcrystalline Al2O3, wherein the Fe and Al metal elements are uniformly distributed in the nanosphere shell.

2. A method for preparing the amorphous composite metal oxide hollow nanosphere material according to claim 1, comprising the following steps: (1) The carbon source is dissolved in deionized water to obtain a carbon source solution. After the carbon source solution undergoes a hydrothermal reaction, it is centrifuged, washed, and dried to obtain a carbon sphere template. The carbon source is one or more of glucose, fructose, sucrose, maltose, starch, and citric acid. The concentration of the carbon source solution is 0.1~5 mol / L. (2) A weak acid salt is dissolved in deionized water to obtain a weak acid salt solution. A pH buffer solution is prepared using the corresponding weak acid. A carbon ball template, an iron source, and an aluminum source are added and stirred evenly. The mixture is then ultrasonically broken up until homogeneous to obtain a mixed solution. The weak acid salt is one or more of sodium citrate, sodium acetate, sodium oxalate, ammonium acetate, and ammonium formate. The concentration of the weak acid salt solution is 0.1~1 mol / L. The corresponding weak acid is one or more of citric acid, acetic acid, oxalic acid, and formic acid. The pH of the pH buffer solution is controlled at 4.0-4.

8. The concentration of the iron source in the mixed solution is 0.1~100 mmol / L, the molar ratio of iron ions to aluminum ions is 0.1~5:1, and the concentration of the carbon ball template is 0.1-5 g / L. (3) The mixed solution is kept at 60~80℃ for 1~3 h. After the heat treatment is completed, the solution is centrifuged, washed and dried to obtain the precursor. The precursor is calcined in air to obtain the amorphous composite metal oxide hollow nanospheres.

3. The preparation method according to claim 2, characterized in that, The hydrothermal reaction is carried out in a sealed reactor at a temperature of 170-190 °C for 1-5 h; and / or the centrifugation is carried out in a centrifuge at a speed of 9000-11000 rpm for 20-40 min; and / or the drying temperature is 70-90 °C for 6-24 h.

4. The preparation method according to claim 2, characterized in that, The iron source is one or more of ferric nitrate, ferric sulfate, ferric chloride, ferrous sulfate, and ferric acetate, and the aluminum source is one or more of aluminum nitrate, aluminum sulfate, aluminum chloride, and alum.

5. The preparation method according to claim 2, characterized in that, The precursor calcination process is carried out in a muffle furnace or a tube furnace, with a calcination temperature of 400~600 ℃ and a calcination time of 1~5 h.

6. The application of the amorphous composite metal oxide hollow nanosphere material according to claim 1 or the amorphous composite metal oxide hollow nanosphere material prepared by the preparation method according to any one of claims 2-5 in the preparation of nano-carbon materials by catalytic cracking of low-carbon hydrocarbons.

7. The application according to claim 6, characterized in that, The specific operation of the application is as follows: (1-1) The amorphous composite metal oxide hollow nanosphere material is added to a fluidized bed reactor, and gas is introduced to carry out the catalyst reduction process; (2-2) After the reduction is completed, a reaction gas is introduced to carry out the synthesis reaction of nano-carbon materials. The reaction gas is a mixture of carbon source gas and inert gas, and the volume ratio of carbon source gas to inert gas is 0.1~10:

1. (3-3) After the reaction is complete, the nano-carbon material is collected, washed with alkali, acid, water and / or anhydrous ethanol, and dried to obtain pure nano-carbon material.

8. The application according to claim 7, characterized in that, The gas used in the reduction process is a mixture of hydrogen and an inert gas, with a volume ratio of hydrogen to inert gas of 0.1 to 2:1, and the flow rate of the mixture during the reduction process is 20 to 40 cm⁻¹. 3 The reduction process is carried out at a temperature of 600-800℃ and a reduction time of 10-60 min; and / or the inert gas is one of nitrogen, argon, or helium; and / or the carbon source gas is one or more of methane, ethane, ethylene, propane, propylene, and butane; and / or the synthesis reaction temperature is 650-1000℃ and the reaction time is 40-180 min; and / or the flow rate of the mixed gas in the synthesis reaction is 20-40 cm⁻¹. 3 / s; and / or the alkaline solution used in the alkaline washing process is sodium hydroxide or potassium hydroxide solution, the concentration of the alkaline solution is 0.5~3 mol / L, the alkaline washing temperature is 65~85 ℃, and the alkaline washing time is 4~24 h; and / or the acid used in the acid washing process is one or more of hydrochloric acid, nitric acid, and sulfuric acid, the concentration of the acid solution is 0.5~3 mol / L, the acid washing temperature is 65~85 ℃, and the acid washing time is 4~24 h; and / or the drying temperature described in step (3-3) is 70~90 ℃, and the drying time is 6~24 h.

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