A core-shell alumina microsphere catalyst and a preparation method thereof, and application thereof in catalytic decomposition of CF4

Abstract

This invention discloses a method for preparing a core-shell alumina microsphere catalyst, comprising the following steps: Step 1, adding aluminum chloride hexahydrate to a mixed solvent of distilled water and anhydrous ethanol, stirring thoroughly at a certain stirring rate until the solution is completely clear, and maintaining the resulting clear solution in a water bath; Step 2, adding propylene oxide to the clear solution to obtain a homogeneous solution, and gelling the resulting homogeneous solution in a water bath; Step 3, after the gelation reaction is completed, immersing the obtained sample in anhydrous ethanol; Step 4, transferring the immersed sample to a muffle furnace, calcining at a certain temperature for a period of time, and cooling to room temperature to obtain the core-shell alumina microsphere catalyst. This invention also discloses a core-shell alumina microsphere catalyst and its application in the catalytic decomposition of CF4. This invention solves the problem of low efficiency in treating CF4 gas using current catalytic hydrolysis methods.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, and in particular relates to a core-shell alumina microsphere catalyst and its preparation method, as well as its application in the catalytic decomposition of CF4. Background Technology

[0002] CF4 is considered the most abundant and harmful of all perfluorinated compounds, possessing a high global warming potential, approximately four orders of magnitude higher than carbon dioxide—and a very long atmospheric lifetime (3,000-50,000 years). Currently, CF4 is listed as a key greenhouse gas for emission reduction, making the decomposition and treatment of perfluorinated hydrocarbon waste gases generated from industrial processes essential.

[0003] Due to its highly symmetrical single-carbon structure, CF4 has a bond energy of 543±4 kJ / mol. -1 This makes it difficult to decompose. Catalytic hydrolysis is considered the most efficient technique for decomposing CF4 due to its high decomposition rate under mild conditions and the small number of harmful chemicals involved. However, the efficiency of catalytic hydrolysis of CF4 is relatively low, and there is an urgent need to develop highly efficient catalysts to improve the efficiency of catalytic hydrolysis of CF4 to solve this problem. Summary of the Invention

[0004] The purpose of this invention is to provide a core-shell alumina microsphere catalyst and its preparation method, as well as its application in the catalytic decomposition of CF4, to solve the problem of low efficiency in treating CF4 gas by current catalytic hydrolysis methods.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a method for preparing a core-shell alumina microsphere catalyst, comprising the following steps:

[0006] Step 1: Add aluminum chloride hexahydrate to a mixed solvent of distilled water and anhydrous ethanol, and stir thoroughly at a certain stirring rate until the solution is completely clear. Keep the resulting clear solution in a water bath.

[0007] Step 2: Add propylene oxide to the clear solution to obtain a homogeneous solution, and then gel the homogeneous solution in a water bath.

[0008] Step 3: After the gelation reaction is complete, immerse the obtained sample in anhydrous ethanol;

[0009] Step 4: Transfer the soaked sample to a muffle furnace, calcine it at a certain temperature for a period of time, and then cool it to room temperature to obtain the core-shell alumina microsphere catalyst.

[0010] Furthermore, in step 1, the temperature of the water bath is 50-70°C, and the stirring rate is 150-300 rpm.

[0011] Further, in step 1, the proportion of aluminum chloride hexahydrate in the mixed solution of distilled water and anhydrous ethanol is 0.4–0.58 g / ml; the volume ratio of distilled water to anhydrous ethanol is 0.6–0.8.

[0012] Furthermore, the temperature of the water bath in step 2 is 50-70°C, and the molar ratio of propylene oxide to aluminum chloride hexahydrate added in step 1 is (4-4.5):1.

[0013] Furthermore, in step 3, the soaking time with anhydrous ethanol is 12-36 hours, and the anhydrous ethanol is replaced every 2-6 hours during the soaking process.

[0014] Furthermore, in step 4, the calcination temperature is 750–850°C, the calcination time is 1–3 hours, and the heating rate of the muffle furnace during calcination is 2–4°C / min.

[0015] The present invention also provides a core-shell alumina microsphere catalyst, which is prepared according to the above preparation method.

[0016] Furthermore, the core-shell alumina microsphere catalyst has an outer shell structure formed by stacked alumina nanosheets and an inner alumina sphere.

[0017] This invention also provides the application of a core-shell alumina microsphere catalyst in the catalytic decomposition of CF4.

[0018] The specific process is as follows:

[0019] Step 1: Fill the core-shell alumina microsphere catalyst into a quartz tube and then insert the quartz tube into the fixed-bed reaction chamber;

[0020] Step 2: A mixture of CF4 and air is pre-introduced into the reaction chamber via the gas path system. The volume concentration of CF4 in the mixture is 0.2-0.5%, the volume concentration of air is 99.5-99.8%, and the flow rate of the mixture is 28.3-38.3 ml / min. After the gas path stabilizes, the fixed-bed reaction chamber is heated to 550-650℃ at a heating rate of 10-15℃ / min. Water is introduced into the vaporization chamber via an injection pump at a rate of 0.6-0.8 ml / h to heat the vaporization chamber to a temperature of 180-220℃. The water vapor generated in the vaporization chamber is then introduced into the reaction chamber.

[0021] Step 3: The tail gas obtained from the reaction chamber is first passed through a deionized water bottle, then dried through a drying tube. The dried gas is then sent to a gas chromatograph to detect the gas components and content.

[0022] The beneficial effects of this invention are:

[0023] The core-shell alumina microspheres prepared by this invention have a diameter of 2-3 μm. The shell of the alumina microsphere is coated with a layer of alumina nanosheets, which helps to increase the specific surface area of ​​the microsphere. The core of the alumina microsphere is a solid alumina microsphere.

[0024] This invention obtains a core-shell alumina microsphere catalyst by adding aluminum chloride hexahydrate to a mixed solution of anhydrous ethanol and distilled water, followed by gelation treatment and calcination. This method has low raw material costs, simple preparation method, and short reaction time. The prepared core-shell alumina microsphere catalyst can achieve 100% efficiency in catalytic decomposition of CF4 in a fixed-bed reaction chamber at 600℃ and maintain this efficiency for 100 hours, demonstrating good catalytic efficiency and stability. This solves the problem of low efficiency in treating CF4 gas by current catalytic hydrolysis methods. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is an X-ray diffraction pattern of the core-shell alumina microsphere catalyst prepared in Example 1 of this invention. In the figure, the horizontal axis 2θ represents the diffraction angle (degree), and the vertical axis Intensity represents the intensity (au).

[0027] Figure 2 These are scanning electron microscope (SEM) images of the core-shell alumina microsphere catalyst prepared in Example 1 of this invention, wherein (a) is an SEM image at a scale of 1 μm, (b) is an SEM image at a scale of 500 nm, and (c) is an SEM image at a scale of 1 μm with the outer shell open.

[0028] Figure 3 This is a transmission electron microscope (TEM) image of the core-shell alumina microsphere catalyst prepared in Example 1 of this invention.

[0029] Figure 4 This is a stability graph of the core-shell alumina microsphere catalyst prepared in Example 1 of this invention for catalytic hydrolysis of CF4. In the graph, the horizontal axis h represents time (hours), and the vertical axis CF4 decomposition represents the decomposition rate of CF4 (%).

[0030] Figure 5The images are scanning electron microscope (SEM) images of the catalysts prepared in Comparative Examples 1 to 3, wherein (a) is an SEM image of the catalyst prepared in Comparative Example 1, (b) is an SEM image of the catalyst prepared in Comparative Example 2, and (c) is an SEM image of the catalyst prepared in Comparative Example 3. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a method for preparing a core-shell alumina microsphere catalyst for catalytic decomposition of CF4, specifically including the following steps:

[0033] Step 1: Add aluminum chloride hexahydrate to a mixed solution of distilled water and anhydrous ethanol, stir thoroughly until the solution is completely clear, and keep the resulting clear solution in a water bath at 50-70°C; wherein the proportion of aluminum chloride hexahydrate added in the mixed solution of distilled water and anhydrous ethanol is 0.4-0.58 g / ml, and the volume ratio of distilled water to anhydrous ethanol is 0.6-0.8; the stirring speed is 150-300 rpm.

[0034] Step 2: Add propylene oxide to the clear solution, and gel the resulting homogeneous solution in a water bath at 50-70°C for 50-70 minutes until the sample is solidified; wherein the molar ratio of propylene oxide to aluminum chloride hexahydrate is (4-4.5):1.

[0035] Step 3: After the gelation reaction is complete, the obtained sample is soaked in anhydrous ethanol. The anhydrous ethanol is replaced every 2 to 6 hours during the soaking process, and the soaking time in anhydrous ethanol is 12 to 36 hours.

[0036] Step 4: Transfer the soaked sample to a muffle furnace and calcine at 750–850℃ for 1–3 hours. After cooling to room temperature, the core-shell alumina microsphere catalyst is obtained. The heating rate of the muffle furnace during calcination is 2–4℃ / min.

[0037] In this invention, according to Oswald ripening, smaller internal particles gradually dissolve and deposit onto larger crystals. Propylene oxide, as a surfactant, induces the hydrolysis and condensation of aluminum chloride hexahydrate to form alumina microspheres, thus leading to the formation of a core-shell structure. Reactions that are too hot or too cold will reduce the efficiency of CF4 decomposition in the synthesized material. Immersion in anhydrous ethanol helps remove air bubbles adhering to the sample surface, effectively cleaning the sample surface and removing any impurities and contaminants. Stirring aims to dissolve aluminum chloride hexahydrate in the solution; the stirring rate has no effect on the final dissolution. The heating rate of the muffle furnace affects the pore size of the catalyst surface; a faster heating rate results in larger pores, while a slower heating rate results in smaller pores.

[0038] Example 1

[0039] This embodiment provides a method for preparing a core-shell alumina microsphere catalyst for catalytic decomposition of CF4, comprising the following steps:

[0040] Step 1: Add aluminum chloride hexahydrate to a mixed solution of distilled water and anhydrous ethanol, with a volume ratio of distilled water to anhydrous ethanol of 0.7. Stir thoroughly until the solution is completely clear. Specifically, stir at a stirring rate of 200 rpm for 1 hour to obtain a mixed reaction solution. The proportion of aluminum chloride hexahydrate in the mixed solution of distilled water and anhydrous ethanol is 0.49 g / ml.

[0041] Step 2: Quickly add propylene oxide to the mixed solution and keep the resulting solution in a 60°C water bath for gelation until the sample is solidified. The molar ratio of propylene oxide to aluminum chloride hexahydrate is 4.25.

[0042] Step 3: After the gelation reaction is complete, the obtained sample is immersed in anhydrous ethanol. The anhydrous ethanol is replaced every 4 hours during the immersion process, and the immersion time is 24 hours.

[0043] Step 4: Transfer the soaked sample to a muffle furnace and calcine it at 800℃ for 2 hours. After cooling to room temperature, a core-shell alumina microsphere catalyst is obtained. The heating rate of the muffle furnace is 3℃ / min.

[0044] The characterization results of the sample synthesized in Example 1 are as follows: Figures 1-3 As shown, XRD characterization of the alumina successfully prepared in this embodiment confirms that the alumina prepared in this embodiment has a spherical core-shell morphology. Figure 2 In the image, (a) is a scanning electron microscope (SEM) image at a scale of 1 μm, (b) is a SEM image at a scale of 500 nm, and (c) is a SEM image at a scale of 1 μm with the outer casing open. Figure 2As can be seen, the surface is a shell-like structure composed of stacked alumina nanosheets, while the interior consists of smooth alumina microspheres. TEM results indicate that the alumina microspheres prepared in this embodiment have a core-shell structure. Measurements show that the diameter of the core in this embodiment is 2.4 μm, the shell thickness is 0.3 μm, and the specific surface area is 302.5729 m². 2 / g.

[0045] Example 2

[0046] The difference between this embodiment and Embodiment 1 is that the ratio of aluminum chloride hexahydrate to the mixed solution of distilled water and anhydrous ethanol in step 1 is 0.4 g / ml, and the stirring rate is 150 rpm.

[0047] Example 3

[0048] The difference between this embodiment and Embodiment 1 is that the ratio of aluminum chloride hexahydrate to the distilled water and anhydrous ethanol mixture in step 1 is 0.58 g / ml, and the stirring rate is 150 rpm.

[0049] Example 4

[0050] The difference between this embodiment and Embodiment 1 is that the volume ratio of distilled water to anhydrous ethanol in step 1 is 0.6.

[0051] Example 5

[0052] The difference between this embodiment and Embodiment 1 is that the volume ratio of distilled water to anhydrous ethanol in step 1 is 0.8.

[0053] Example 6

[0054] The difference between this embodiment and Embodiment 1 is that in step 2, the obtained homogeneous solution is kept at 50°C for gelation.

[0055] Example 7

[0056] The difference between this embodiment and Embodiment 1 is that in step 2, the obtained homogeneous solution is kept at 70°C for gelation.

[0057] Example 8

[0058] The difference between this embodiment and Embodiment 1 is that in step 4, the soaked sample is transferred to a muffle furnace and calcined at 750°C for 2 hours.

[0059] Example 9

[0060] The difference between this embodiment and Embodiment 1 is that in step 4, the soaked sample is transferred to a muffle furnace and calcined at 850°C for 2 hours.

[0061] Example 10

[0062] The difference between this embodiment and embodiment 1 is that in step 4, the soaked sample is transferred to a muffle furnace, and the heating rate of the muffle furnace is 2℃ / min.

[0063] Example 11

[0064] The difference between this embodiment and embodiment 1 is that in step 4, the soaked sample is transferred to a muffle furnace, and the heating rate of the muffle furnace is 4°C / min.

[0065] Example 12

[0066] The difference between this embodiment and embodiment 1 is that the soaking time in anhydrous ethanol in step 3 is 12 hours, and the anhydrous ethanol is replaced every 2 hours during the soaking process.

[0067] Example 13

[0068] The difference between this embodiment and embodiment 1 is that the soaking time in anhydrous ethanol in step 3 is 36 hours, and the anhydrous ethanol is replaced every 6 hours during the soaking process.

[0069] Example 14

[0070] The difference between this embodiment and embodiment 1 is that in step 4, the soaked sample is transferred to a muffle furnace and calcined for 1 hour.

[0071] Example 15

[0072] The difference between this embodiment and embodiment 1 is that in step 4, the soaked sample is transferred to a muffle furnace and calcined for 3 hours.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that the ratio of aluminum chloride hexahydrate to the mixed solution of distilled water and anhydrous ethanol in step 1 is 3.53 g / ml.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 is that the volume ratio of distilled water to anhydrous ethanol in step 1 is 0.5.

[0077] Comparative Example 3

[0078] The difference between this comparative example and Example 1 is that in step 2, the resulting homogeneous solution is kept at 80°C for gelation.

[0079] like Figure 5 As shown in (a) to (c), these are scanning electron microscope images of comparative examples 1 to 3, respectively. It can be seen from the images that they cannot form a core-shell structure.

[0080] Comparative Example 4

[0081] 1.5 g of F127 (surfactant), 75 mL of tetrahydrofuran, and 12 mL of concentrated hydrochloric acid (36-38 wt%) were mixed and stirred at room temperature for 30 minutes to obtain a clear and transparent mixture. Then, 2.0 g of aluminum isopropoxide was added, and stirring was continued for one hour. The mixture was transferred to a constant temperature drying oven and placed at 40 °C for 48 h to obtain a white single micelle gel. 1.0 g of single micelle gel and 100 mg of phenolic resin spheres were dispersed in a mixed solution of 30 mL of ethanol and 100 mL of water, and then transferred to a hydrothermal reactor and hydrothermally heated at 160 °C for 24 h. The resulting product was washed with anhydrous ethanol and then calcined at 700 °C for 3 h under a nitrogen atmosphere to remove the surfactant, yielding a phenolic resin microsphere@mesoporous alumina composite material.

[0082] Comparative Example 4 uses the invention patent with publication number CN113548684A, entitled "A Mesoporous Alumina-Based Core-Shell Composite Material and Its Single-Micelle Guided Interface Assembly Method and Application." Comparative Example 4 uses a template method to synthesize alumina microspheres. According to its description and accompanying drawings, the alumina composite material prepared therefrom is mesoporous and spherical. Compared to the core-shell alumina microspheres prepared in this invention, although both are microspheres, the microspheres of this invention are synthesized without a template. Furthermore, the surface of the product of this invention is urchin-like, increasing the specific surface area of ​​the material, which is more conducive to the catalytic decomposition of CF4, and it contains an alumina core. Combined with... Figure 2 As can be seen from the accompanying drawings of Comparative Example 4, the core-shell alumina microspheres prepared in this invention are not the same as the mesoporous alumina prepared in Comparative Example 4.

[0083] Comparative Example 5

[0084] Weigh 2g each of coconut shell charcoal and aluminum acetate, and 0.2645g of PVP (polyvinylpyrrolidone). Pour the coconut shell charcoal, aluminum acetate, and N-vinylpyrrolidone into 100ml of pure water and stir magnetically for 12 hours to obtain a mixed solution.

[0085] The mixed solution was poured into a reaction vessel, which was then placed in an oven and heated at 180°C for 8 hours for hydrothermal treatment to obtain a heat-treated solution. The solid product obtained after filtration of the heat-treated solution was washed four times alternately with hot water and alcohol, and then dried to obtain a dried product. A tube furnace was evacuated to a vacuum state, and then N2 was introduced before the dried product was placed in the tube furnace for calcination to obtain carbon-based supported alumina. The N2 flow rate was 100 ml / min, the calcination temperature was 500°C, the heating rate was 5°C / min, and the heating time was 120 min.

[0086] 1.5g of the prepared carbon-based supported alumina was placed in a low-temperature plasma reactor. The discharge voltage was adjusted to 25kV, and flue gas was introduced into the plasma reactor, wherein the volume percentage of CF4 in the CF4 flue gas was 10%. CF4 was then degraded by dielectric barrier discharge to obtain the degraded tail gas, wherein the volume-to-mass ratio of CF4 to carbon-based supported alumina was 500ml:1g, and the flow rate of the CF4 flue gas was 10ml / min.

[0087] The exhaust gas was detected using gas chromatography, with readings taken every five minutes. The highest CF4 degradation rate was measured to be 78%.

[0088] Comparative Example 5 uses the invention patent with publication number CN115970670A, entitled "Carbon-based Supported Alumina and its Preparation Method, and its Application in CF4 Degradation". Comparative Example 5 combines activated carbon and alumina in a supported manner. The alumina has no special morphology. Furthermore, this method combines plasma decomposition with plasma. In contrast, this invention uses a one-step method to directly synthesize alumina microspheres with a core-shell structure and uses thermocatalytic decomposition technology to decompose CF4. Plasma and thermocatalysis are two completely different technologies. Moreover, the material synthesized by this technology does not have an alumina core-shell structure. Therefore, it is completely different from the method of this invention. At the same time, the highest catalytic efficiency of Comparative Example 5 is only 78%, which is far lower than the catalytic efficiency of the core-shell alumina microspheres prepared in this application (see Experimental Examples 1-3 below for details).

[0089] The core-shell alumina microspheres formed in this invention, with alumina both inside and out, are unprecedented and represent a highly innovative material. Furthermore, the core-shell structure enhances the catalytic performance for CF4 decomposition, demonstrating superior performance compared to existing technologies. It achieves 100% efficiency in the thermocatalytic decomposition of CF4 at 600℃ and maintains this efficiency for 100 hours. The catalyst structure remains unchanged after the reaction, indicating structural stability and excellent performance. This is the first study in the field of thermocatalytic CF4 decomposition where a special morphology enhances catalytic performance, showcasing significant innovation.

[0090] The present invention also provides a method for catalytic decomposition of CF4, comprising the following steps:

[0091] (1) The core-shell alumina microsphere catalyst is packed into a quartz tube and the quartz tube is placed into the reaction chamber of the fixed bed;

[0092] (2) A mixture of CF4 and air is pre-introduced into the gas path system. The volume concentration of CF4 in the mixture is 0.2-0.5%, the volume concentration of air is 99.5-99.8%, and the flow rate of the mixture is 28.3-38.3 ml / min. After the gas path stabilizes, the fixed-bed reaction chamber is heated to 550-650℃ at a heating rate of 10-15℃ / min. Water is introduced into the vaporization chamber through an injection pump at a rate of 0.6-0.8 ml / h to heat the vaporization chamber at a temperature of 180-220℃. Water vapor is then introduced into the reaction chamber.

[0093] (3) The tail gas obtained by catalytic hydrolysis of CF4 is first passed through a deionized water bottle and then dried through a drying tube. The dried gas is then entered into a gas chromatograph to detect the composition and content of the gas.

[0094] Experimental Example 1

[0095] (1) The core-shell alumina microsphere catalysts prepared in Examples 1 to 15 were packed into a quartz tube and the quartz tube was placed into the reaction chamber of the fixed bed.

[0096] (2) A mixture of CF4 and air is pre-introduced into the gas path system. The volume concentration of CF4 in the mixture is 0.25%, the volume concentration of air is 99.5%, and the flow rate of the mixture is 28.3 ml / min. After the gas path stabilizes, the fixed bed reaction chamber is heated to 550℃ at a heating rate of 10℃ / min. Water is introduced into the vaporization chamber through an injection pump at a rate of 0.6 ml / h to heat the vaporization chamber at a temperature of 180℃. Water vapor is then introduced into the reaction chamber.

[0097] (3) The tail gas obtained by catalytic hydrolysis of CF4 is first passed through a deionized water bottle and then dried through a drying tube. The dried gas is then entered into a gas chromatograph to detect the composition and content of the gas.

[0098] Experiment Example 2

[0099] (1) The core-shell alumina microsphere catalysts prepared in Examples 1 to 15 were packed into a quartz tube and the quartz tube was placed into the reaction chamber of the fixed bed.

[0100] (2) A mixture of CF4 and air is pre-introduced into the gas path system. The volume concentration of CF4 in the mixture is 0.25%, the volume concentration of air is 99.75%, and the flow rate of the mixture is 33.3 ml / min. After the gas path stabilizes, the fixed bed reaction chamber is heated to 600℃ at a heating rate of 12℃ / min. Water is introduced into the vaporization chamber through an injection pump at a rate of 0.7 ml / h to heat the vaporization chamber at a temperature of 200℃. Water vapor is then introduced into the reaction chamber.

[0101] (3) The tail gas obtained by catalytic hydrolysis of CF4 is first passed through a deionized water bottle and then dried through a drying tube. The dried gas is then entered into a gas chromatograph to detect the composition and content of the gas.

[0102] Experimental Example 3

[0103] (1) The core-shell alumina microsphere catalysts prepared in Examples 1 to 15 were packed into a quartz tube and the quartz tube was placed into the reaction chamber of the fixed bed.

[0104] (2) A mixture of CF4 and air is pre-introduced into the gas path system. The volume concentration of CF4 in the mixture is 0.2%, the volume concentration of air is 99.8%, and the flow rate of the mixture is 38.3 ml / min. After the gas path stabilizes, the fixed bed reaction chamber is heated to 650°C at a heating rate of 15°C / min. Water is introduced into the vaporization chamber through an injection pump at a rate of 0.8 ml / h to heat the vaporization chamber at a temperature of 220°C. Water vapor is then introduced into the reaction chamber.

[0105] (3) The tail gas obtained by catalytic hydrolysis of CF4 is first passed through a deionized water bottle and then dried through a drying tube. The dried gas is then entered into a gas chromatograph to detect the composition and content of the gas.

[0106] Tables 1-3 show the decomposition efficiencies of the core-shell alumina microsphere catalysts used in Examples 1-15 and Comparative Examples 1-3 at reaction temperatures of 550, 600, and 650 °C, respectively, for the hydrolysis of CF4. As can be seen from the tables, the core-shell alumina microsphere catalysts prepared in the examples of this invention exhibit excellent performance in the hydrolysis of CF4, especially at 600 °C, where the decomposition efficiency of the products for CF4 in each example is above 90%. Meanwhile, in Comparative Examples 1-3, since core-shell alumina microspheres were not prepared, the decomposition efficiency of the products for CF4 was significantly reduced. This demonstrates that the core-shell structure has a significant impact on the catalytic efficiency of CF4.

[0107] Other examples Figure 4 As shown, the core-shell alumina microsphere catalyst prepared in Example 1 of this invention achieves a 100% decomposition efficiency for catalytic hydrolysis of CF4 at a reaction temperature of 600℃, and can maintain this efficiency for 100 hours, demonstrating good catalytic decomposition efficiency and stability.

[0108] Table 1. Performance data of the core-shell alumina microsphere catalyst for catalytic hydrolysis of CF4 in Experimental Example 1.

[0109]

[0110]

[0111] Table 2 Performance data of the core-shell alumina microsphere catalyst for CF4 hydrolysis in Experiment Example 2

[0112] Example <![CDATA[Decomposition efficiency (%) of catalytic hydrolysis of CF4 at 600 °C]]> Example 1 100 Example 2 96 Example 3 95 Example 4 95 Example 5 90 Example 6 94 Example 7 93 Example 8 90 Example 9 94 Example 10 98 Example 11 95 Example 12 93 Example 13 96 Example 14 95 Example 15 92 Comparative Example 1 60 Comparative Example 2 65 Comparative Example 3 55

[0113] Table 3. Performance data of the core-shell alumina microsphere catalyst for catalytic hydrolysis of CF4 in Experiment Example 3.

[0114] Example <![CDATA[Decomposition efficiency (%) of catalytic hydrolysis of CF4 at 650 °C]]> Example 1 89 Example 2 90 Example 3 85 Example 4 84 Example 5 90 Example 6 89 Example 7 88 Example 8 90 Example 9 85 Example 10 87 Example 11 80 Example 12 84 Example 13 82 Example 14 85 Example 15 86 Comparative Example 1 57 Comparative Example 2 62 Comparative Example 3 60

[0115] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0116] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell alumina microsphere catalyst, characterized in that, Includes the following steps: Step 1: Add aluminum chloride hexahydrate to a mixed solvent of distilled water and anhydrous ethanol, and stir thoroughly at a certain stirring rate until the solution is completely clear. Keep the resulting clear solution in a water bath. Step 2: Add propylene oxide to the clear solution to obtain a homogeneous solution, and then gel the obtained homogeneous solution in a water bath. Step 3: After the gelation reaction is complete, immerse the obtained sample in anhydrous ethanol; Step 4: Transfer the soaked sample to a muffle furnace, calcine it at a certain temperature for a period of time, and then cool it to room temperature to obtain the core-shell alumina microsphere catalyst. In step 1, the temperature of the water bath is 50-70℃, and the stirring speed is 150-300 rpm; in step 1, the proportion of aluminum chloride hexahydrate in the mixed solution of distilled water and anhydrous ethanol is 0.4-0.58 g / mL; and the volume ratio of distilled water to anhydrous ethanol is 0.6-0.

8. The temperature of the water bath in step 2 is 50~70℃, and the molar ratio of propylene oxide to aluminum chloride hexahydrate added in step 1 is (4~4.5):1; In step 3, the soaking time with anhydrous ethanol is 12-36 hours, and the anhydrous ethanol is replaced every 2-6 hours during the soaking process. In step 4, the calcination temperature is 750~850℃, the calcination time is 1~3h, and the heating rate of the muffle furnace during calcination is 2~4℃ / min.

2. A core-shell alumina microsphere catalyst, characterized in that, It is prepared according to the preparation method according to claim 1.

3. The core-shell alumina microsphere catalyst according to claim 2, characterized in that, The core-shell alumina microsphere catalyst has an outer shell structure made up of stacked alumina nanosheets and an inner alumina sphere.

4. The application of a core-shell alumina microsphere catalyst as described in claim 2 or 3 in the catalytic decomposition of CF4.

5. The application according to claim 4, characterized in that, The specific process is as follows: Step 1: Fill the core-shell alumina microsphere catalyst into a quartz tube and then insert the quartz tube into the fixed-bed reaction chamber; Step 2: A mixture of CF4 and air is pre-introduced into the reaction chamber via the gas path system. The volume concentration of CF4 in the mixture is 0.2-0.5%, the volume concentration of air is 99.5-99.8%, and the flow rate of the mixture is 28.3-38.3 mL / min. After the gas path stabilizes, the fixed-bed reaction chamber is heated to 550-650℃ at a heating rate of 10-15℃ / min. Water is introduced into the vaporization chamber via an injection pump at a rate of 0.6-0.8 mL / h to heat the vaporization chamber to a temperature of 180-220℃. The water vapor generated in the vaporization chamber is then introduced into the reaction chamber. Step 3: The tail gas obtained from the reaction chamber is first passed through a deionized water bottle, then dried through a drying tube. The dried gas is then sent to a gas chromatograph to detect the gas components and content.

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