Sodium modified mesoporous aluminum and its preparation method and application

Abstract

The present invention provides a sodium-modified mesoporous aluminum and its preparation method and application, wherein the sodium-modified mesoporous aluminum comprises a mesoporous aluminum substrate and metallic sodium, wherein the metallic sodium is uniformly dispersed in the mesoporous aluminum substrate, and the mesoporous aluminum substrate is an amorphous porous nanoparticle; the mass ratio of oxygen element on the surface of the sodium-modified mesoporous aluminum is 44.88%, and the specific surface area of ​​the mesoporous aluminum substrate is ≥100m 2 / g, and the pore size of the mesoporous aluminum substrate is 2 to 50 nm. The sodium-modified mesoporous aluminum provided by the present invention can maintain a high catalytic rate for a long time, has a long life, and has significant effects and is worthy of promotion.

Description

Technical Field

[0001] The invention relates to the application field of a catalyst for decomposing carbon tetrachloride, and in particular to sodium-modified mesoporous aluminum, a preparation method and application thereof. Background Art

[0002] Carbon tetrafluoride is a potent greenhouse gas with a global warming potential (GWP) thousands of times greater than that of carbon dioxide. Its atmospheric lifetime is extremely long, reaching tens of thousands of years. Therefore, degrading carbon tetrafluoride is of great significance for mitigating global warming and reducing the greenhouse effect.

[0003] However, carbon tetrafluoride has low reactivity and high stability, making it difficult to degrade into harmless or low-harm substances. Due to the high electronegativity of the fluorine atom (F) in the carbon tetrafluoride molecule and the high bond energy of the carbon-fluorine bond (CF bond), this high bond energy makes the CF bond extremely difficult to break at room temperature and pressure, making carbon tetrafluoride not prone to chemical reactions. In addition, the carbon tetrafluoride molecule has a regular tetrahedral spatial structure, with four fluorine atoms symmetrically distributed around the carbon atom. This symmetrical structure makes the carbon tetrafluoride molecule highly stable in both physical and chemical properties.

[0004] Existing technologies for carbon tetrafluoride degradation use alumina as a catalyst coupled with plasma technology. Although activated alumina is a highly effective fluoride adsorbent, it still suffers from low efficiency when treating carbon tetrafluoride. Limited by its adsorption capacity, once the alumina reaches saturation, its decomposition efficiency drops significantly, further impacting the carbon tetrafluoride treatment effect. Furthermore, the hydroxyl groups on the surface of activated alumina are unstable. When oxygen is present in the flue gas, the plasma easily destroys these surface hydroxyls, rapidly deactivating the activated alumina.

[0005] Based on the above, it is urgent to study a sodium-modified mesoporous aluminum and its preparation method and application to solve the above problems. Summary of the Invention

[0006] The main purpose of the present invention is to provide a sodium-modified mesoporous aluminum and its preparation method and application, aiming to solve the technical problem of low efficiency in degrading carbon tetrafluoride after catalyst saturation in conventional technologies.

[0007] To achieve the above object, the present invention provides a sodium-modified mesoporous aluminum, comprising a mesoporous aluminum substrate and metallic sodium, wherein the metallic sodium is uniformly dispersed in the mesoporous aluminum substrate, and the mesoporous aluminum substrate is an amorphous porous nanoparticle;

[0008] The mass proportion of oxygen elements on the surface of the sodium-modified mesoporous aluminum is 40% to 50%, the mass proportion of sodium elements on the surface of the sodium-modified mesoporous aluminum is 1 to 20%, and the specific surface area of ​​the mesoporous aluminum substrate is ≥100m 2 / g, and the pore diameter of the mesoporous aluminum substrate is 2-50 nm.

[0009] Furthermore, the mass proportion of sodium element on the surface of the sodium-modified mesoporous aluminum is 3-5%.

[0010] The present invention provides a method for preparing sodium-modified mesoporous aluminum as described above, comprising the steps of:

[0011] Mixing polyether, nitric acid, aluminum isopropoxide and metal nitrate to obtain a mixture;

[0012] The mixture is stirred, dried and calcined in sequence to obtain sodium-modified mesoporous aluminum;

[0013] The metal nitrate includes sodium nitrate, and the ratio of the added amounts of the polyether, the nitric acid, the aluminum isopropoxide and the sodium nitrate is 1g:1.5ml:10mmol:0.01-0.05g, wherein the concentration of the nitric acid is 65%.

[0014] Furthermore, the calcination temperature is 500-1000° C., and the calcination time is 1-8 hours.

[0015] Furthermore, in the step of mixing the polyether, nitric acid, aluminum isopropoxide and metal nitrate to obtain a mixture, the polyether is dissolved in a solvent, and the nitric acid, aluminum isopropoxide and metal nitrate are added under stirring; wherein the mass volume ratio of the polyether to the solvent is 0.01 to 1 g / ml.

[0016] Furthermore, the temperature of the drying treatment is 50 to 80° C., and the duration of the drying treatment is 6 to 12 hours.

[0017] Furthermore, the temperature of the calcination treatment includes 600° C., and the calcination treatment includes: heating the solid particles obtained by the drying treatment to 600° C. at a heating rate of 1-10° C. / min, and calcining for 3 to 6 hours to obtain the sodium-modified mesoporous aluminum.

[0018] The present invention also provides a use of sodium-modified mesoporous aluminum prepared by any of the preparation methods described above in carbon tetrafluoride treatment, comprising the steps of:

[0019] The carbon tetrafluoride-containing flue gas to be treated flows through the sodium-modified mesoporous aluminum in a plasma field for decomposition treatment, wherein the flow rate of the carbon tetrafluoride-containing flue gas in the plasma field is 10 to 50 mL / min, and the concentration of carbon tetrafluoride in the carbon tetrafluoride-containing flue gas is 1% to 20%;

[0020] The sodium-modified mesoporous aluminum is placed in the discharge region of the plasma field.

[0021] Furthermore, the input voltage of the plasma reactor for forming the low-temperature plasma field is 20-40 kV.

[0022] Furthermore, the oxygen concentration in the carbon tetrafluoride-containing flue gas is 5%-20%.

[0023] The beneficial effects achieved by the present invention are:

[0024] The sodium-modified mesoporous aluminum provided by the present invention has high efficiency in decomposing carbon tetrafluoride. The surface of the sodium-modified mesoporous aluminum is rich in hydroxyl groups, so it has excellent performance when applied to CF4 degradation. With the doping of sodium element, the presence of Na is conducive to the activation of adsorbed water, promotes the formation of surface hydroxyl groups, increases the acidic and basic site content of mesoporous aluminum, and further promotes the decomposition of CF4. At the same time, after sodium element doping, the surface oxygen content of the mesoporous aluminum base is significantly improved, which significantly enhances the decomposition effect of carbon tetrafluoride, breaking through the decomposition efficiency peak of alumina when applied to carbon tetrafluoride degradation in conventional technologies (that is, under specific conditions, the highest efficiency point reached by carbon tetrafluoride being degraded or decomposed, indicating the proportion of carbon tetrafluoride being removed or converted within a certain period of time).

[0025] The sodium-modified mesoporous aluminum provided by the present invention has high catalytic activity and long life. The surface oxygen content of the sodium-modified mesoporous aluminum is 44.88%, and the sodium content accounts for 3.25%. Based on the increase in surface oxygen after sodium doping, Na doping promotes the combination of carbon and oxygen in CF4 to generate gas escape, significantly reducing carbon deposition. This synergistically increases the total acid content and strong acid content in the mesoporous aluminum after sodium doping, effectively mitigating the catalyst poisoning problem caused by carbon and fluorine deposition during the catalytic reaction process in conventional technologies, improving the catalytic activity of the sodium-modified mesoporous aluminum and enabling it to maintain a high catalytic rate for a long time.

[0026] The morphology of the mesoporous aluminum substrate in the sodium-modified mesoporous aluminum of the present invention is optimized. With the doping of sodium element, sodium is evenly dispersed in the mesoporous aluminum substrate, and the specific surface area of ​​the mesoporous aluminum substrate is ≥100m 2 / g, the mesoporous aluminum substrate has a pore size of 2 to 50 nm, and the morphology of the mesoporous aluminum substrate is transformed into dispersed porous nanoparticles. The optimized morphology of the modified mesoporous aluminum substrate provides ample active sites for the adsorption and catalysis of carbon tetrafluoride, thereby improving the activity of the catalyst. In addition, as the specific surface area of ​​the mesoporous aluminum substrate increases, the dispersion of the carbon tetrafluoride particles also increases, which helps to evenly distribute the carbon tetrafluoride on the catalyst surface, reducing mass transfer resistance and further improving degradation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0028] Figure 1 This is a morphology detection diagram of each metal-doped mesoporous aluminum catalyst using SEM-EDS in Analysis Example 1 of the present invention, wherein: Figure 1 (a) is the SEM image of mesoporous aluminum. Figure 1 (b) is the SEM image of Na / mesoporous aluminum. Figure 1 (c) is the SEM image of Ce / mesoporous aluminum. Figure 1 (d) is the EDS image of mesoporous aluminum. Figure 1 (e) is the EDS image of Na / mesoporous aluminum. Figure 1 (f) is the EDS image of Ce / mesoporous aluminum;

[0029] Figure 2 This is the XRD analysis diagram of each metal-doped mesoporous aluminum catalyst in Analysis Example 1 of the present invention.

[0030] Figure 3 The microscopic morphology of each metal-doped mesoporous aluminum catalyst obtained by TEM in the analysis example 1 of the present invention is shown in FIG. Figure 3 (a) is the TEM image of mesoporous aluminum. Figure 3 (b) is the TEM image of Na / mesoporous aluminum. Figure 3 (c) is the TEM image of Ce / mesoporous aluminum.

[0031] Figure 4 (a) is a schematic diagram showing the effect of different synthesis methods on the decomposition efficiency of Na / mesoporous aluminum on CF4 in Analysis Example 2 of the present invention. Figure 4 (b) is a schematic diagram showing the effect of different sodium doping concentrations of Na / mesoporous aluminum on the decomposition efficiency of CF4 in Analysis Example 2 of the present invention.

[0032] Figure 5 (a) is a schematic diagram showing the decomposition efficiency of carbon tetrafluoride by Na / mesoporous aluminum, mesoporous aluminum, and plasma alone at a flow rate of 20 mL / min in Analysis Example 3 of the present invention; Figure 5 (b) Analysis of the present invention in Example 3 flow rate of 50mL / minNa / mesoporous aluminum, mesoporous aluminum and a single plasma decomposition efficiency of carbon tetrafluoride schematic.

[0033] Figure 6 (a) Schematic diagram comparing the decomposition efficiency of carbon tetrafluoride by various metal-doped mesoporous aluminum at a flue gas flow rate of 20 mL / min in Analysis Example 3 of the present invention; Figure 6(b) is a schematic diagram comparing the decomposition efficiency of carbon tetrafluoride by various metal-doped mesoporous aluminum when the flue gas flow rate is 50 mL / min in Analysis Example 3 of the present invention.

[0034] Figure 7 Schematic diagram showing the effect of the oxygen composition of carbon tetrafluoride on the decomposition efficiency of carbon tetrafluoride in Na / mesoporous aluminum or plasma alone in Analysis Example 4 of the present invention.

[0035] Figure 8 Schematic diagram of the effect of O2 on the decomposition performance of different metal-doped mesoporous aluminum CF4 in analysis example 4 of the present invention, where Figure 8 (a) Comparison of CF4 degradation efficiency of various metal-doped mesoporous aluminum under oxygen-containing flue gas conditions; Figure 8 (b) Comparison of CF4 degradation efficiency of composite metal-doped mesoporous aluminum under oxygen-containing flue gas conditions.

[0036] Figure 9 This is the SEM detection image of Na / mesoporous aluminum before and after the reaction under the condition of O2 concentration of 10% in the analysis example 5 of the present invention, wherein Figure 9 (a) is the morphology of Na / mesoporous aluminum before reaction. Figure 9 (b) The morphology after Na / mesoporous aluminum reaction.

[0037] Figure 10 This is a diagram showing the changes in element content before and after the Na / mesoporous aluminum reaction in analysis example 5 of the present invention.

[0038] Figure 11 These are SEM images of Na / mesoporous aluminum before and after the reaction in Analysis Example 5 of the present invention.

[0039] Figure 12 The XRD patterns and TEM patterns of Na / mesoporous aluminum before and after the reaction under the condition of 10% O2 concentration in Example 6 of the present invention are shown, wherein: Figure 12 (a) is the XRD diffraction pattern of Na / mesoporous aluminum after reaction; Figure 12 (b) TEM image of Na / mesoporous aluminum after reaction.

[0040] Figure 13 This is a graph showing the changes in the surface acid sites of Na / mesoporous aluminum before and after the reaction under the condition of an O2 concentration of 10% in Example 7 of the present invention, wherein: Figure 13 (a) is the NH3-TPD diagram of Na / mesoporous aluminum, Ce / mesoporous aluminum and mesoporous aluminum before reaction. Figure 13 (b) NH3-TPD diagram before Na / mesoporous aluminum reaction.

[0041] Figure 14 This is a graph showing the change in Na / mesoporous aluminum acidity before and after the reaction under the condition of 10% O2 concentration in Example 7 of the present invention, wherein: Figure 14(a) is the infrared spectrum of pyridine adsorption before Na / mesoporous aluminum reaction. Figure 14 (b) is the infrared spectrum of pyridine adsorption after Na / mesoporous aluminum reaction.

[0042] Figure 15 This is the analysis diagram of the Na / mesoporous aluminum alkaline site before and after the reaction in Analysis Example 7 of the present invention, where Figure 15 (a) is the CO2-TPD diagram of mesoporous aluminum and Na / mesoporous aluminum, Figure 15 (b) CO2-TPD diagram of Na / mesoporous aluminum before and after reaction.

[0043] Figure 16 This is the XPS graph of Na / mesoporous aluminum before and after the reaction under the condition of 10% O2 concentration in Example 8 of the present invention, wherein, Figure 16 (a) is the 2p orbital electron energy spectrum of Na / mesoporous aluminum before and after the reaction. Figure 16 (b) is the 1s orbital electron energy spectrum of Na / mesoporous aluminum oxide before and after the reaction. Figure 16 (c) is the 1s orbital electron energy spectrum of Na / mesoporous aluminum sodium element before and after the reaction. Figure 16 (d) is the 1s orbital electron energy spectrum of Na / mesoporous aluminum fluoride element.

[0044] Figure 17 (a) is the NH3-TPD diagram of O2-pretreated and untreated Na / mesoporous aluminum in Analytical Example 9 of the present invention; Figure 17 (b) CO2-TPD of O2-pretreated and untreated Na / mesoporous aluminum in Analytical Example 9 of the present invention.

[0045] Figure 18 This is the gas chromatogram of the decomposition of CF4 tail gas by metal-doped mesoporous aluminum in Analysis Example 9 of the present invention.

[0046] Figure 19 This is a comparison of the decomposition efficiency of CF4 using mesoporous aluminum and commercial Al2O3 as catalysts in Analysis Example 10 of the present invention.

[0047] Figure 20 (a) is the NH3-TPD test graph of mesoporous aluminum before and after the reaction in Analysis Example 11 of the present invention; Figure 20 (b) is the NH3-TPD test graph of mesoporous aluminum and commercial Al2O3 in Analysis Example 11 of the present invention.

[0048] The realization of the objectives, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0050] It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments may be combined with each other. It should also be understood that the terms used in the embodiments of the present invention are intended to describe specific embodiments, rather than to limit the scope of protection of the present invention.

[0051] Unless otherwise defined, all technical and scientific terms used in the present invention are consistent with the prior art knowledge and description of the present invention by those skilled in the art. The present invention may also be implemented using any prior art methods, devices, and materials that are similar or equivalent to the methods, devices, and materials described in the embodiments of the present invention. It should be understood by those skilled in the art that, as an explanation of the present application document, without affecting the actual understanding of the technical solution of the present application, "Intensity (au)" may be expressed as intensity, "Stress" may be expressed as stress, "Strain" may be expressed as strain, "Grain size" may be expressed as grain size, and "Frequency" may be expressed as frequency.

[0052] When numerical ranges are given in the examples, it should be understood that unless otherwise specified herein, both endpoints of each numerical range and any value between the two endpoints may be used. The test methods in the following examples, for which specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers. The materials or reagents required in the following examples were all commercially available unless otherwise specified.

[0053] During the continued use of alumina catalysts in conventional technologies, carbon tetrafluoride degrades to produce carbon deposits or other byproducts. These carbon deposits gradually accumulate on the catalyst surface, covering some active sites, reducing the catalyst's effective surface area and gradually decreasing its reaction activity. Furthermore, the increase in carbon deposits can also reduce the catalyst's pores, further affecting the contact between reactants and active sites, thereby reducing catalytic efficiency and ultimately leading to a significant decrease in the decomposition efficiency of alumina and deactivation of the alumina catalyst.

[0054] Specifically, referring to Analysis Example 10 of the present invention, the decomposition efficiency of the alumina catalyst dropped to below 50% at 300 min, which is equivalent to the decomposition efficiency of CF4 by plasma alone, indicating that Al2O3 has been deactivated at this time.

[0055] To solve the above problems, the present invention provides a sodium-modified mesoporous aluminum, comprising a mesoporous aluminum substrate and a metal, wherein the metal is uniformly dispersed in the mesoporous aluminum substrate, the mesoporous aluminum substrate is porous nanoparticles in an amorphous state, and the metal comprises sodium;

[0056] The mass proportion of oxygen elements on the surface of the sodium-modified mesoporous aluminum is 40% to 50%.

[0057] Exemplarily, the mass proportion of oxygen elements on the surface of the sodium mesoporous aluminum is 44.88%.

[0058] The sodium-modified mesoporous aluminum provided by the present invention has high efficiency in decomposing carbon tetrafluoride. The surface of the sodium-modified mesoporous aluminum is rich in hydroxyl groups, so it has excellent performance when applied to CF4 degradation. With the doping of sodium element, the presence of Na is conducive to the activation of adsorbed water, promotes the formation of surface hydroxyl groups, increases the acidic and basic site content of mesoporous aluminum, and further promotes the decomposition of CF4. At the same time, after sodium element doping, the surface oxygen content of the mesoporous aluminum base is significantly improved, which significantly enhances the decomposition effect of carbon tetrafluoride, breaking through the decomposition efficiency peak of alumina when applied to carbon tetrafluoride degradation in conventional technologies (that is, under specific conditions, the highest efficiency point reached by carbon tetrafluoride being degraded or decomposed, indicating the proportion of carbon tetrafluoride being removed or converted within a certain period of time).

[0059] The sodium-modified mesoporous aluminum provided by the present invention has high catalytic activity and a long lifespan. The surface oxygen content of the sodium-modified mesoporous aluminum is 44.88%. Based on the increased surface oxygen content after sodium doping, Na doping promotes the combination of carbon and oxygen in CF4 to generate gaseous escape, significantly reducing carbon deposition. This synergistic effect of sodium doping on the total acid content and strong acid content in the mesoporous aluminum effectively mitigates the catalyst poisoning problem caused by carbon and fluorine deposition during the catalytic reaction process in conventional technologies, thereby enhancing the catalytic activity of the sodium-modified mesoporous aluminum and maintaining a high catalytic rate for a long time.

[0060] Specifically, referring to the research in Analytical Example 3 of the present invention, the sodium-modified mesoporous aluminum can reach a stable value of about 60% after 500 minutes, overcoming the catalyst poisoning problem caused by C and F deposition.

[0061] In some embodiments, the specific surface area is ≥ 100 m 2 / g, and the pore diameter of the mesoporous aluminum substrate is 2-50 nm.

[0062] like Figure 1As shown in (b), with the addition of sodium, the sodium is evenly dispersed in the mesoporous aluminum substrate, and the morphology of the mesoporous aluminum substrate is transformed into dispersed porous nanoparticles. The optimized morphology resulting from the modified mesoporous aluminum substrate provides ample active sites for the adsorption and catalysis of carbon tetrafluoride, thereby improving the activity of the catalyst. Furthermore, as the specific surface area of ​​the mesoporous aluminum substrate increases, the dispersion of the carbon tetrafluoride particles also increases, which helps to evenly distribute the carbon tetrafluoride on the catalyst surface, reducing mass transfer resistance and further improving degradation efficiency.

[0063] In some embodiments, the metal of the sodium-modified mesoporous aluminum includes sodium, and the sodium element in the sodium-modified mesoporous aluminum (ie, Na / mesoporous aluminum, the same below) modified with sodium may account for 3-5%.

[0064] For example, the mass fraction of O element on the surface of Na / mesoporous aluminum is 44.88%, and the mass fraction of Na element is 3.25%.

[0065] The present invention provides a method for preparing sodium-modified mesoporous aluminum, comprising the steps of:

[0066] S1. Mixing polyether, nitric acid, aluminum isopropoxide and metal nitrate to obtain a mixture.

[0067] In some embodiments, the metal nitrate includes sodium nitrate, and the ratio of the added amounts of the polyether, the nitric acid, the aluminum isopropoxide, and the sodium nitrate is 1 g:1.5 ml:10 mmol:0.01-0.05 g, wherein the concentration of the nitric acid is 65%.

[0068] In the step of mixing the polyether, nitric acid, aluminum isopropoxide and metal nitrate to obtain the mixture, the polyether can be dissolved in a solvent, and the nitric acid, aluminum isopropoxide and metal nitrate are added under stirring; wherein the mass volume ratio of the polyether to the solvent is 0.01 to 1 g / ml.

[0069] Illustratively, the solvent may be ethanol.

[0070] Illustratively, the concentration of nitric acid may be 65%.

[0071] S2. The mixture is stirred, dried and calcined in sequence to obtain sodium-modified mesoporous aluminum.

[0072] The calcination temperature is 600-800° C., and the calcination time is 1-8 hours.

[0073] Exemplarily, the stirring treatment may include the steps of: covering the mixture with plastic wrap and stirring at room temperature for about 6 hours.

[0074] The temperature of the drying process may be 50 to 80° C., and the duration of the drying process may be 6 to 12 hours.

[0075] In some embodiments, the calcination temperature includes 600° C., and the calcination includes heating the solid particles obtained by the drying treatment to 600° C. at a heating rate of 2° C. / min, and calcining for 3 to 6 hours to obtain the sodium-modified mesoporous aluminum.

[0076] The present invention also provides the use of sodium-modified mesoporous aluminum prepared by the above preparation method in carbon tetrafluoride treatment, comprising the steps of:

[0077] The flue gas containing carbon tetrafluoride to be treated flows through the sodium-modified mesoporous aluminum in a plasma field for decomposition treatment.

[0078] In some embodiments, the flow rate of the carbon tetrafluoride-containing flue gas in the plasma field may be 10-50 mL / min, the concentration of carbon tetrafluoride in the carbon tetrafluoride-containing flue gas may be 1%-20%, and the oxygen concentration in the carbon tetrafluoride-containing flue gas may be 5%-20%.

[0079] For example, the concentration of oxygen in the flue gas containing carbon tetrafluoride may be 10%.

[0080] Referring to the research in Analysis Example 4 of the present invention, it can be seen that an appropriate concentration of O2 can improve the decomposition efficiency and reaction stability of CF4 by sodium-modified mesoporous aluminum.

[0081] It can also be referred to the research in Analysis Example 8 of the present invention. It can be seen that after Na doping, Al-OH is converted into a double-bridged hydroxyl group between Na and Al (HO-μbri(Na-Al)), which increases the stability of -OH in Na / mesoporous aluminum, making it less likely to be destroyed by O2, and further improving the decomposition efficiency and reaction stability of CF4 by sodium-modified mesoporous aluminum under O2 conditions.

[0082] In contrast, in conventional technologies, due to the electronegativity of O₂, when the O₂ concentration in the reaction system reaches a certain level, it competes with CF₄, reducing the energy of the plasma acting on CF₄ and resulting in a decrease in the plasma's efficiency in decomposing CF₄. Furthermore, the O₂ introduced under the action of the plasma reacts with the mesoporous aluminum, altering the surface active sites of the mesoporous aluminum and reducing its efficiency in decomposing CF₄.

[0083] The mesoporous aluminum may be placed in a discharge region of the plasma field.

[0084] In some embodiments, the input voltage of the plasma reactor for forming the plasma field may be 20-40 kV.

[0085] For further understanding of the present invention, now illustrate with examples:

[0086] Example 1

[0087] Preparation of sodium-modified mesoporous aluminum by doping method

[0088] 1g of polyether P123 was dissolved in 20mL of ethanol at room temperature. 1.5mL of 65% nitric acid, 2.04g (10mmol) of aluminum isopropoxide, and 0.025g of sodium nitrate were added under vigorous stirring. Cover the mixture with plastic wrap, stir at room temperature for about 6h, and then heat it in a drying oven at 60°C for two days to evaporate the solution. Finally, the resulting solid particles were calcined at 600°C at a heating rate of 2°C / min for 5h to obtain a sodium-modified mesoporous aluminum product - Na / mesoporous aluminum, wherein the sodium doping concentration of Na / mesoporous aluminum was 3-5%, that is, the mass fraction of sodium element in the surface elements of Na / mesoporous aluminum accounted for 3-5%.

[0089] The above steps remain unchanged, except that 0.025 g of sodium nitrate is replaced with 0.434 g of cerium nitrate to obtain cerium-modified mesoporous aluminum - Ce / mesoporous aluminum.

[0090] Comparative Example 1

[0091] The other steps in Example 1 remained unchanged, except that 0.025 g of sodium nitrate was replaced with 0.12 mL of manganese nitrate to obtain manganese-doped mesoporous aluminum - Mn / mesoporous aluminum.

[0092] Among them, the doping concentration of metal elements in Ce / mesoporous aluminum and Mn / mesoporous aluminum is about 5%.

[0093] Comparative Example 2

[0094] Preparation of sodium-modified mesoporous aluminum by loading method

[0095] 1 g of polyether P123 was dissolved in 20 mL of ethanol at room temperature. While stirring the solution, 1.5 mL of 65% nitric acid and 2.04 g (10 mmol) of aluminum isopropoxide were added. The mixture was covered with plastic wrap and stirred at room temperature for approximately 6 hours. Afterwards, the mixture was heated in a 60°C drying oven for 2 days to evaporate the solution. Finally, the resulting solid particles were calcined at 600°C for 5 hours at a heating rate of 2°C / min to produce mesoporous aluminum.

[0096] Mesoporous aluminum was dispersed in 50 mL of deionized water and sonicated for 30 minutes. After the solid was completely dissolved, 0.025 g of NaNO₃ was added and sonicated for another 30 minutes. The resulting suspension was poured into a rotary evaporator and evaporated at 75°C for 2 hours. Finally, the resulting solid sample was calcined at 600°C for 5 hours at a heating rate of 2°C / min to obtain Na-loaded mesoporous aluminum.

[0097] Comparative Example 3

[0098] The other steps in Example 1 remained unchanged, and only the amount of sodium nitrate added was changed to obtain Na / mesoporous aluminum with sodium doping amounts of 2%, 10% and 20%, respectively.

[0099] Analysis example 1

[0100] The morphology of metal-doped mesoporous aluminum catalysts was determined by SEM-EDS. Figure 1 As shown, Figure 1 (a) is the SEM image of mesoporous aluminum. Figure 1 (b) is the SEM image of Na / mesoporous aluminum. Figure 1 (c) is the SEM image of Ce / mesoporous aluminum. Figure 1 (d) is the EDS image of mesoporous aluminum. Figure 1 (e) is the EDS image of Na / mesoporous aluminum. Figure 1 (f) is the EDS image of Ce / mesoporous aluminum.

[0101] The mesoporous aluminum surface exhibits a large number of pores. The introduction of Na or Ce transforms the surface morphology into dispersed nanoparticles, demonstrating that metal doping alters the morphology of mesoporous aluminum. EDS results show that the surface oxygen content of the mesoporous aluminum is 26.81%, and the Al content is 59.85%. After Na doping, the O content of the Na / mesoporous aluminum surface increases to 44.88%, while the Na content accounts for 3.25%. After Ce doping, the O content of the Ce / mesoporous aluminum surface increases to 43.61%, while the Ce content accounts for 7.84%.

[0102] The results show that both Na and Ce doping will change the morphology of mesoporous aluminum and significantly increase the surface oxygen content, which is an important factor in enhancing the catalytic decomposition of CF4 by mesoporous aluminum.

[0103] The physical structures of the above catalysts were analyzed by XRD. Figure 2 The XRD spectrum of mesoporous aluminum shows no obvious characteristic peaks, indicating that the mesoporous aluminum is in an amorphous state. Similarly, no characteristic peaks belonging to aluminum oxide appear when Na, Mn, and Ce are added. Furthermore, no characteristic peaks belonging to Na, Mn, and Ce oxides appear, indicating that Na, Mn, and Ce do not change the phase structure of the mesoporous aluminum and are uniformly dispersed into the mesoporous aluminum matrix.

[0104] The microstructure of the above catalysts was analyzed by TEM. Figure 3 As shown, Figure 3 (a) is the TEM image of mesoporous aluminum. Figure 3 (b) is the TEM image of Na / mesoporous aluminum. Figure 3(c) is a TEM image of Ce / mesoporous aluminum. The mesoporous aluminum exhibits a typical wormhole-like microstructure with no surface lattice fringes, indicating its porous and amorphous structure. After Na doping, the mesoporous aluminum retains the wormhole-like microstructure and lacks distinct diffraction rings, indicating an amorphous structure. Ce doping, however, makes the material more compact while still maintaining an amorphous state.

[0105] Analysis example 2

[0106] Study on the effects of different synthesis methods on the decomposition efficiency of carbon tetrafluoride in Example 1 (doping method) and Comparative Example 2 (loading method)

[0107] Flue gas containing carbon tetrafluoride with a CF4 concentration of 10% and a flue gas flow rate of 50 mL / min flows through a plasma field to couple Na / mesoporous aluminum or Na-loaded mesoporous aluminum, wherein the plasma field is formed by a plasma reactor with an input voltage of 25 kV.

[0108] like Figure 4 As shown, Figure 4 (a) is the effect of the synthesis method on the decomposition efficiency of CF4, Figure 4 (b) Effect of doping concentration. The peak CF4 decomposition efficiency of Na / mesoporous aluminum prepared by the doping method reached 76%, 6% higher than that of mesoporous aluminum. In contrast, the decomposition efficiency of Na / mesoporous aluminum prepared by the loading method was only 62%, 8% lower than that of mesoporous aluminum.

[0109] The loading method first synthesizes mesoporous aluminum and then loads sodium onto the surface. This makes it easier for sodium to aggregate on the surface of the mesoporous aluminum and clog the pores, thereby reducing the catalyst's CF4 decomposition efficiency. The doping method directly adds sodium to the solution used to prepare the mesoporous aluminum. This makes the sodium more dispersed in the catalyst, increasing the contact area between sodium and CF4 and improving the CF4 decomposition efficiency.

[0110] The effect of Na doping concentration on CF4 decomposition efficiency was studied. Figure 4 (b) When the Na doping level is 5%, the Na / mesoporous aluminum achieves a maximum CF4 decomposition efficiency of 76%, which is 13%, 20%, and 16% higher than when the Na doping levels are 2%, 10%, and 20%, respectively. Too low a doping concentration is insufficient to achieve the desired modification effect, while too high a concentration can cause particle agglomeration, thus affecting catalytic efficiency. Therefore, doping with 5% Na is the best method for preparing Na / mesoporous aluminum catalysts.

[0111] Analysis example 3

[0112] Study on the effect of flue gas flow rate on the decomposition efficiency of carbon tetrafluoride

[0113] Flue gas with a concentration of 10% flows through plasma field coupled Na / mesoporous aluminum, plasma field coupled mesoporous aluminum and single low-temperature plasma field respectively.

[0114] like Figure 5 As shown, Figure 5 (a) is the decomposition efficiency of CF4 by Na / mesoporous aluminum and mesoporous aluminum at a flow rate of 20 mL / min. Figure 5 (b) Decomposition efficiency of CF4 at a flow rate of 50 mL / min for Na / mesoporous aluminum and mesoporous aluminum.

[0115] When the flue gas flow rate is 20mL / min, the decomposition efficiency of CF4 by mesoporous aluminum reaches a peak of 82% after 100 minutes of reaction, and the mesoporous aluminum is close to deactivation after 500 minutes. Under the same conditions, the decomposition efficiency of CF4 by Na / mesoporous aluminum reaches a peak of 86% after 150 minutes, and reaches a stable value of about 60% after 500 minutes. When the flue gas flow rate is increased to 50mL / min, the peak decomposition efficiency of CF4 by mesoporous aluminum can reach 70%, but it will still be deactivated after 500 minutes of reaction. The peak decomposition efficiency of CF4 by Na / mesoporous aluminum is about 76%, and after 500 minutes of reaction, the decomposition efficiency can still be above 40%, maintaining a certain catalytic activity. This indicates that Na doping is not It not only improves the decomposition efficiency of CF4, but also prolongs the life of the catalyst, maintaining a higher catalytic efficiency over a long period of time.

[0116] Flue gas with a concentration of 10% flows through the plasma field coupled Na / mesoporous aluminum, Mn / mesoporous aluminum, Ce / mesoporous aluminum, and mesoporous aluminum respectively.

[0117] like Figure 6 As shown, Figure 6 (a) Comparison of metal-doped mesoporous aluminum at a flue gas flow rate of 20 mL / min; Figure 6 (b) Comparison of metal-doped mesoporous aluminum at a flue gas flow rate of 50 mL / min.

[0118] As can be seen, when the flue gas flow rate is 20 mL / min, the CF4 decomposition efficiency of Mn / mesoporous aluminum reaches a peak of 75% after 100 minutes of reaction and stabilizes at approximately 60% after 400 minutes of reaction. The CF4 decomposition efficiency of Ce / mesoporous aluminum reaches a peak of 70% after 110 minutes of reaction and stabilizes at approximately 60% after 400 minutes of reaction. Although both Mn / mesoporous aluminum and Ce / mesoporous aluminum fall below the maximum decomposition efficiency of 82% for mesoporous aluminum, they maintain high catalytic efficiency with extended reaction time. After 400 minutes of reaction, the decomposition efficiency is 10% higher than that of mesoporous aluminum. When the flow rate is increased to 50 mL / min, the maximum decomposition efficiency of Mn / mesoporous aluminum and Ce / mesoporous aluminum decreases to 60% and 62%, respectively, lower than the maximum decomposition efficiency of 72% for mesoporous aluminum. After 400 minutes of reaction, the decomposition efficiency of both Mn / mesoporous aluminum and Ce / mesoporous aluminum reaches 50%, also 10% higher than that of mesoporous aluminum.

[0119] The experimental results show that Mn and Ce cannot improve the oxidation activity of mesoporous aluminum to CF4, but can prolong the catalytic reaction. This may be because both Mn and Ce can increase the surface oxygen content, thereby strengthening the oxidation of surface carbon and reducing carbon The poisonous effect of deposition on catalysts.

[0120] Analysis example 4

[0121] The effect of oxygen on the decomposition efficiency of carbon tetrafluoride was studied.

[0122] Under the conditions of CF4 concentration of 10%, O2 concentration of 10% and flow rate of 50mL / min, the flue gas containing tetrafluoride flows through the plasma field to couple Na / mesoporous aluminum. Figure 7 As shown in the figure, it can be seen that under oxygen-free conditions, the decomposition efficiency of CF4 by plasma alone is 30%, and the decomposition efficiency drops to 26% after the introduction of O2. Under oxygen-free conditions, the highest decomposition efficiency of CF4 by Na / mesoporous aluminum coupled plasma is 76%, and the decomposition efficiency drops to 46% after 400 minutes of reaction. After the introduction of O2, the highest decomposition efficiency of CF4 by Na / mesoporous aluminum coupled plasma increases to 81%, and the decomposition efficiency remains stable at 60% after 400 minutes of reaction. That is, O2 improves the catalyst Decomposition efficiency and reaction stability of CF4.

[0123] Under the conditions of CF4 concentration of 10%, O2 concentration of 10% and flow rate of 50mL / min, flue gas containing carbon tetrafluoride flows through plasma field coupled Na / mesoporous aluminum, plasma field coupled mesoporous aluminum, plasma field coupled Mn / mesoporous aluminum, plasma field coupled Ce / mesoporous aluminum and single plasma field respectively to study the effect of O2 on the CF4 decomposition performance of different metal-doped mesoporous aluminum, such as Figure 8 As shown, Figure 8 (a) Comparison of CF4 degradation efficiency of metal-doped mesoporous aluminum under oxygen-containing flue gas conditions; Figure 8 (b) Comparison of CF4 degradation efficiency of composite metal-doped mesoporous aluminum under oxygen-containing flue gas conditions.

[0124] It can be seen that the decomposition efficiency of CF4 by mesoporous aluminum coupled plasma is 58%, and after 400 minutes of reaction, the decomposition efficiency is the same as that under the action of plasma alone, indicating that the mesoporous aluminum has been deactivated at this time. The highest decomposition efficiency of CF4 by Mn / mesoporous aluminum and Ce / mesoporous aluminum is 58%, and they are also deactivated after 400 minutes of reaction. The effects of Na, Ce, Mn, and multi-metal doping on the CF4 decomposition performance of mesoporous aluminum were studied, such as Figure 8 As shown in (b), Co-doping with Na, Ce and Mn did not improve the CF4 decomposition activity of the catalyst, but was The catalytic activity of Na-doped mesoporous aluminum is even weaker.

[0125] Analysis example 5

[0126] The morphology of Na / mesoporous aluminum before and after the reaction under the condition of 10% O2 concentration in analysis example 4 was studied by SEM. Figure 9 As shown, Figure 9 (a) is the morphology of Na / mesoporous aluminum before reaction. Figure 9(b) is the morphology after Na / mesoporous aluminum reaction. Visible reaction The nanoparticles on the surface of Na / mesoporous aluminum are closely arranged before the reaction, and there is no obvious change on the surface of Na / mesoporous aluminum after the reaction, indicating that the reaction has not Changing the morphology of Na / mesoporous aluminum .

[0127] XPS was used to analyze the changes in element content before and after the Na / mesoporous aluminum reaction. Figure 10 As shown. Before the reaction, Na / mesoporous aluminum exhibited characteristic peaks at 75.08eV, 285.12eV, 532.56eV, and 1072.15eV, belonging to Al 2p, C 1s, O 2p, and Na 1s, respectively. After the reaction, the intensity of the characteristic peak of O1s was significantly weakened, and a characteristic peak belonging to F1s appeared at 687.08eV. The changes in elemental content before and after the reaction of Na / mesoporous aluminum were further analyzed, as shown in Table 1. After CF4 decomposition, the Al and O element contents on the surface of Na / mesoporous aluminum decreased by 15.15% and 26.62%, respectively, indicating that both elements participated in the CF4 decomposition reaction. The C element content increased from 10.25% to 13.26%, an increase of 3.01%, which is far lower than the 30% increase in carbon element after the mesoporous aluminum reaction. This indicates that Na doping promotes the combination of C and O in CF4 to generate gas escape, significantly reducing C deposition. After the reaction, the proportion of F elements on the surface of Na / mesoporous aluminum is 39.87%, which is much higher than the 10.07% increase in F on the mesoporous aluminum after the reaction. Although more F is deposited on the surface of Na / mesoporous aluminum, Na / mesoporous aluminum has a higher catalytic efficiency. This indicates that Na can slow down the poisoning of mesoporous AlF.

[0128] The element contents before and after the Na / mesoporous aluminum reaction are shown in Table 1.

[0129] Table 1 Element contents before and after Na / mesoporous aluminum reaction

[0130]

[0131] The morphology of mesoporous aluminum before and after the reaction at an O2 concentration of 10% in Example 4 was studied by SEM. Figure 11 As shown in the figure, after the reaction, the pores on the surface of the mesoporous aluminum are corroded, and a large amount of C and F are deposited on the surface of the mesoporous aluminum to form a dense layer. Say again It is clear that Na doping can alleviate the catalyst poisoning problem caused by C and F deposition during the catalytic reaction process. .

[0132] Analysis example 6

[0133] The morphology of Na / mesoporous aluminum before and after the reaction at an O2 concentration of 10% in Example 4 was studied by XRD and TEM.

[0134] like Figure 12 As shown, Figure 12 (a) is the XRD diffraction pattern of Na / mesoporous aluminum after reaction; Figure 12(b) is a TEM image of the Na / mesoporous aluminum after the reaction. The XRD diffraction pattern of the Na / mesoporous aluminum before the reaction lacks distinct characteristic peaks, indicating an amorphous state. After the reaction, distinct characteristic peaks emerge at 17°, 21°, and 23°, corresponding to AlF3-PDF47-1659, indicating the formation of AlF3. Figure 12 (b) shows that the lattice spacing of Na / mesoporous aluminum is 0.41 nm, which is consistent with the AlF3(201) crystal plane spacing corresponding to 21.4° in the XRD diffraction pattern, further proving that the new substance generated is AlF3.

[0135] Analysis example 7

[0136] The changes of the surface acid sites of Na / mesoporous aluminum before and after the reaction under the condition of 10% O2 concentration in analysis example 4 were studied by NH3-TPD. Figure 13 As shown, Figure 13 (a) is the NH3-TPD diagram of Na / mesoporous aluminum, Ce / mesoporous aluminum and mesoporous aluminum before reaction. Figure 13 (b) NH3-TPD diagram before Na / mesoporous aluminum reaction.

[0137] Mesoporous aluminum has obvious characteristic peaks at 350℃-500℃, corresponding to strong acid sites with a content of 1.79mmol / g. Compared with mesoporous aluminum, the strong acid content of Na / mesoporous aluminum increases to 1.91mmol / g, and weak acid sites appear at 100-150℃ with a content of 0.28mmol / g. This shows that Na doping increases the acid content on the surface of mesoporous aluminum and promotes the decomposition of CF4. Compared with mesoporous aluminum, the strong acid content of Ce / mesoporous aluminum decreases by 0.96mmol / g, and weak acid sites appear with a content of 0.26mmol / g. This shows that Ce doping reduces the strong acid content of mesoporous aluminum, thereby reducing its decomposition efficiency of CF4. After the reaction, the weak acid content on the surface of Na / mesoporous aluminum increased to 0.35mmol / g, while the strong acid content decreased to 1.28mmol / g. This indicates that strong acidic sites are involved in the decomposition of CF4 .

[0138] The changes in the acidic species of Na / mesoporous aluminum before and after the reaction under the condition of 10% O2 concentration in analysis example 4 were studied by NH3-TPD. Figure 14 As shown, Figure 14 (a) is the infrared spectrum of pyridine adsorption before Na / mesoporous aluminum reaction. Figure 14 (b) is the infrared spectrum of pyridine adsorption after Na / mesoporous aluminum reaction.

[0139] Table 2 shows the Na / mesoporous aluminum L acid and B acid contents in this analysis example.

[0140] Table 2 Na / mesoporous aluminum L acid and B acid content before and after reaction

[0141]

[0142]

[0143] The basic sites of Na / mesoporous aluminum before and after the reaction were analyzed by CO2-TPD. Figure 15 As shown, Figure 15 (a) is the CO2-TPD diagram of mesoporous aluminum and Na / mesoporous aluminum, Figure 15 (b) CO2-TPD diagram of Na / mesoporous aluminum before and after reaction.

[0144] It can be seen that mesoporous aluminum has CO2 desorption peaks corresponding to weak and strong basic sites at 100°C and 400°C, with contents of 0.85mmol / g and 0.5mmol / g, respectively. Compared with mesoporous aluminum, the weak base content of Na / mesoporous aluminum increases to 1.15mmol / g, and the strong base content increases to 1.2mmol / g. The presence of Na is beneficial to the activation of adsorbed water, which can promote the formation of surface hydroxyl groups and increase The -OH content on the surface of mesoporous aluminum was increased. After the reaction, the weak basic sites of Na / mesoporous aluminum disappeared, and the content of strong basic sites increased to 2.15mmol / g. This shows that -OH participates in the decomposition of CF4, giving H protons to play an acidic role, and then participates in the oxidation reaction after giving protons. At the same time, the alkaline site may also come from the active oxygen ions generated by plasma-excited O2. These oxygen ions Will adsorb on the surface and form new oxygen sites.

[0145] Analysis example 8

[0146] Mechanism Analysis of Decomposition of Carbon Tetrafluoride by Na / Mesoporous Aluminum

[0147] XPS was used to study the Na / mesoporous aluminum before and after the reaction under the condition of 10% O2 concentration in analysis example 4. Figure 16 As shown, Figure 16 (a) is the 2p orbital electron energy spectrum of Na / mesoporous aluminum before and after the reaction. Figure 16 (b) is the 1s orbital electron energy spectrum of Na / mesoporous aluminum oxide before and after the reaction. Figure 16 (c) is the 1s orbital electron energy spectrum of Na / mesoporous aluminum sodium element before and after the reaction. Figure 16 (d) is the 1s orbital electron energy spectrum of Na / mesoporous aluminum fluoride element.

[0148] It can be seen that the main peak of Al 2p orbital before the reaction is located at 74.24eV, corresponding to Al-OH, and moves to 76.18eV after the reaction, corresponding to AlF3, indicating that Al-OH participates in the decomposition reaction of CF4 and loses electrons to transform into AlF3. Figure 16 (b) is the O1s spectrum. Before the reaction, the characteristic peaks at 530.95eV and 531.79eV correspond to O ads and -OH, accounting for 31.4% and 68.6% respectively. Compared with mesoporous aluminum (see Table 4), the -OH content of Na / mesoporous aluminum increased by 12.6%. It is further proved that Na doping increases the surface -OH content .

[0149] After the reaction, the -OH content of the Na / mesoporous aluminum decreased from 69.6% to 34.1%, and a CO characteristic peak appeared at 533.73 eV, accounting for 28.2%. This suggests that -OH participated in the CF₄ decomposition reaction, combining with carbon in CF₄ to convert into CO. Before the reaction, the Na 1s peak at 1071.39 eV, attributed to Na-OH, shifted to 1071.81 eV after the reaction, corresponding to NaF. After Na doping, Al-OH Transformed into double bridged hydroxyl groups between Na and Al (HO-μbri(Na-Al)), which increased the stability of -OH in Na / mesoporous aluminum, making it Not easily destroyed by O2 , maintaining a higher CF4 decomposition efficiency under O2, and O2 itself can promote carbon deposit oxidation under the action of plasma, so after Na doping, O2 changes from an inhibitory effect to a promoting effect. Figure 16 As shown in d, there are two characteristic peaks in F1s after the reaction, namely NaF

[107] (683.88eV) and AlF3 (686.43eV), accounting for 8.4% and 91.6%, respectively, indicating that Na-OH participated in the decomposition reaction of CF4 and converted into NaF, which enabled Na / mesoporous aluminum to maintain a higher catalytic activity during long-term reactions.

[0150] Table 3 shows the element valence ratio of Na / mesoporous aluminum before and after the reaction.

[0151] Table 3 Element valence ratio of Na / mesoporous aluminum before and after reaction

[0152]

[0153] Table 4 XPS bond valence content analysis of mesoporous aluminum

[0154]

[0155]

[0156] Analysis example 9

[0157] Analysis of Oxygen-Promoted Decomposition of Carbon Tetrafluoride

[0158] In order to study the reason why O2 promotes the decomposition of CF4 by Na / mesoporous aluminum coupled plasma, Na / mesoporous aluminum was pretreated with plasma in 10% O2 and 90% Ar atmosphere, and the changes in its acid and basic site content were analyzed. Figure 17 As shown, Figure 17 (a) NH3-TPD graph of O2-pretreated and untreated Na / mesoporous aluminum; Figure 17 (b) CO2-TPD of Na / mesoporous aluminum treated with O2 and without O2 treatment. Figure 17As shown in (a), after O2 pretreatment, the weak acid site content of Na / mesoporous aluminum increased from 0.28mmol / g to 0.35mmol / g, while the strong acid site content remained unchanged. This shows that under the action of plasma, O2 does not affect the strong acid site content of Na / mesoporous aluminum. Figure 17 As shown in (b), after O2 pretreatment, the content of weakly basic sites corresponding to -OH in Na / mesoporous aluminum decreased by 0.03 mmol / g, while the content of weakly basic sites in mesoporous aluminum decreased by 0.8 mmol / g after O2 pretreatment. Na doping increases the stability of -OH, thereby significantly reducing the content of -OH destroyed by O2. Since O2 is beneficial to the oxidation of carbon on the catalyst surface, it promotes the decomposition of CF4. Therefore, O2 can convert the inhibitory effect of O2 into a promoting effect on the catalytic decomposition of CF4 by Na / mesoporous aluminum.

[0159] In order to study the effect of catalyst on CF4 decomposition products under aerobic and anaerobic conditions, the gas chromatogram of CF4 tail gas was analyzed, such as Figure 18 As shown in Figure 2, under anaerobic conditions, the products of CF4 decomposition on Na / mesoporous aluminum contain CO2, CO, and CH2F2. Upon addition of oxygen, the characteristic peaks of CO and CH2F2 disappear, while the CO2 peak increases. The products of CF4 decomposition on Ce / mesoporous aluminum have the same peaks as those on Na / mesoporous aluminum, indicating that the catalyst does not affect the products of CF4 decomposition.

[0160] In summary, Na doping increases the -OH content in mesoporous aluminum and forms a double-bridged hydroxyl group (HO-μbri(Na-Al)). The Na / mesoporous aluminum surface is present in a state, which enhances the stability of -OH. The increase in O content in Na / mesoporous aluminum promotes the combination of C in CF4 with O to generate gas escape, reducing C deposition. After the reaction, Na / mesoporous aluminum combines with F in CF4 to generate NaF and AlF3 that are deposited on the catalyst surface.

[0161] Under the action of the plasma, CF₄ is excited to react, breaking the C₂ bond. The F atom reacts with -OH to form HF, which then combines with Al and Na to form AlF₃ and NaF, which are deposited on the catalyst surface. Some C atoms are directly deposited on the catalyst surface, while some react with O after the -OH breaks, forming CO and CO₂, which escape. Some of the incompletely decomposed CF₄ combines with -OH to form CH₂F₂. When O₂ is introduced, CH₂F₂ and CO are oxidized, converting to CO₂.

[0162] Analysis example 10

[0163] Mesoporous aluminum prepared in Comparative Example 2, commercial Al2O3, and a catalytic-free material (blank control group; the figure shows a single plasma) were respectively coupled to a plasma reactor with an input voltage of 25 kV to carry out a comparative experiment on the decomposition of carbon tetrafluoride.

[0164] That is, a 10% carbon tetrafluoride gas was flowed at a flow rate of 10 mL / min through the mesoporous aluminum (shown as mesoporous aluminum), commercial Al2O3 (shown as commercial Al2O3), and a catalytic material-free material (blank control group; shown as plasma alone) prepared in Example 1, all of which were in a low-temperature plasma field formed by a plasma reactor with an input voltage of 25 kV, to perform carbon tetrafluoride decomposition treatment, and the decomposition efficiency was recorded from 0 to 600 min of treatment, as shown in detail. Figure 19 shown.

[0165] according to Figure 19 As shown, the CF4 decomposition efficiency of mesoporous aluminum rapidly increases to 85% within the first 200 minutes, then slowly increases over about 400 minutes to reach a peak of approximately 99%. Under the same conditions, the peak decomposition efficiency of commercial Al2O3 for CF4 is only 74%, and after 300 minutes, the decomposition efficiency drops below 50%, which is comparable to the decomposition efficiency of plasma alone, indicating that the commercial Al2O3 has been deactivated at this point.

[0166] The comparison of specific surface area, pore volume and pore size of commercial alumina and mesoporous aluminum is shown in Table 5.

[0167] Table 5 Comparison of specific surface area, pore volume and pore diameter of catalysts

[0168]

[0169] Analysis example 11

[0170] NH3-TPD was used to analyze the changes in the surface element composition of mesoporous aluminum before and after the reaction in Analysis Example 4, when the CF4 concentration was 10%, the oxygen concentration was 10%, and the flue gas flow rate was 20 ml / min. Figure 20 As shown in the figure, before the reaction, the mesoporous aluminum surface exhibited a characteristic peak at 300-500°C, corresponding to strong acid sites with a content of 1.79 mmol / g. After the reaction, the content of strong acid sites on the mesoporous aluminum surface decreased to 1.11 mmol / g, and a new characteristic peak corresponding to weak acid sites appeared at 100°C, with a content of 0.35 mmol / g. These results indicate that strong acid sites participate in the CF4 decomposition reaction.

[0171] This example also performs NH3-TPD test on the commercial alumina in Analysis Example 10, as shown in FIG. Figure 20 As shown in the NH3-TPD test, the NH3 desorption peak of commercial alumina appears at a higher temperature than that of mesoporous aluminum, and the strong acid site content is 1.54 mmol / g, which is much lower than that of mesoporous aluminum. The mesoporous aluminum surface contains a higher content of strong acid, thus showing higher CF4 catalytic activity.

[0172] The specific conclusions are as follows:

[0173] (1) The Na / mesoporous aluminum prepared by doping with 5% Na has the best catalytic performance. It not only improves the decomposition efficiency of CF4, but also prolongs the life of the catalyst, allowing it to maintain a higher catalytic efficiency for a long time. Mn and Ce doping does not improve the oxidation activity of mesoporous aluminum towards CF4, but can prolong the effective time of the catalytic reaction. After the introduction of O2, the decomposition efficiency and reaction stability of Na / mesoporous aluminum towards CF4 are improved, while the decomposition activity of Mn / mesoporous aluminum and Ce / mesoporous aluminum towards CF4 is not improved.

[0174] (2) Na doping is beneficial to the activation of adsorbed water, which can promote the formation of surface hydroxyl groups, increase the content of mesoporous aluminum acidic and basic sites, and thus promote the decomposition of CF4.

[0175] The Al-OH in mesoporous aluminum is transformed into a double-bridged hydroxyl group between Na and Al (HO-μbri(Na-Al)), which enhances the stability of -OH. After the introduction of O2, the strong acidic sites and hydroxyl content of Na / mesoporous aluminum do not change significantly, enabling it to maintain a higher CF4 decomposition efficiency under O2.

[0176] (3) Na doping promotes the combination of O and C in CF4, generating gas escape and significantly reducing C deposition. After the reaction, Na / mesoporous aluminum combines with F in CF4 to generate NaF and AlF3 deposited on the catalyst surface, significantly increasing the surface F deposition. However, Na / mesoporous aluminum has a higher catalytic efficiency, indicating that Na can slow down the F poisoning of mesoporous aluminum.

[0177] In summary, the above technical solutions of the present invention are only preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention's description and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. Application of sodium-modified mesoporous aluminum in carbon tetrafluoride treatment, characterized in that: Including steps: The carbon tetrafluoride-containing flue gas to be treated flows through the sodium-modified mesoporous aluminum in a plasma field for decomposition treatment. The flow rate of the carbon tetrafluoride-containing flue gas in the plasma field is 10-50 mL / min, and the concentration of carbon tetrafluoride in the carbon tetrafluoride-containing flue gas is 1%-20%. The sodium-modified mesoporous aluminum is placed in the discharge region of the plasma field; The sodium-modified mesoporous aluminum comprises a mesoporous aluminum substrate and metallic sodium, wherein the metallic sodium is uniformly dispersed in the mesoporous aluminum substrate, and the mesoporous aluminum substrate is porous nanoparticles in an amorphous state; The mass proportion of oxygen elements on the surface of the sodium-modified mesoporous aluminum is 40% to 50%, the mass proportion of sodium elements on the surface of the sodium-modified mesoporous aluminum is 1% to 20%, and the specific surface area of ​​the mesoporous aluminum substrate is ≥100m 2 / g, the pore size of the mesoporous aluminum substrate is 2-50 nm; The preparation method of the sodium-modified mesoporous aluminum comprises the following steps: Mixing polyether, nitric acid, aluminum isopropoxide and metal nitrate to obtain a mixture; The mixture is stirred, dried and calcined in sequence to obtain the sodium-modified mesoporous aluminum; The metal nitrate includes sodium nitrate, and the added amount ratio of the polyether, the nitric acid, the aluminum isopropoxide and the sodium nitrate is 1g:1.5ml:10mmol:0.01-0.05g.

2. The use of sodium-modified mesoporous aluminum in carbon tetrafluoride treatment according to claim 1, characterized in that: The mass proportion of sodium element on the surface of the sodium-modified mesoporous aluminum is 3-5%.

3. The use of sodium-modified mesoporous aluminum in carbon tetrafluoride treatment according to claim 1, characterized in that: The concentration of the nitric acid comprises 65%.

4. The use of sodium-modified mesoporous aluminum in carbon tetrafluoride treatment according to claim 1, characterized in that: The calcination temperature is 500-1000° C., and the calcination time is 1-8 hours.

5. The use of sodium-modified mesoporous aluminum in carbon tetrafluoride treatment according to claim 4, characterized in that: In the step of mixing the polyether, nitric acid, aluminum isopropoxide, and metal nitrate to obtain a mixture, the polyether is dissolved in a solvent, and the nitric acid, aluminum isopropoxide, and metal nitrate are added under stirring; wherein the mass volume ratio of the polyether to the solvent is 0.01-1 g / ml.

6. The use of sodium-modified mesoporous aluminum in carbon tetrafluoride treatment according to claim 4, characterized in that: The temperature of the drying process is 50-80° C., and the duration of the drying process is 6-12 hours.

7. The use of sodium-modified mesoporous aluminum in carbon tetrafluoride treatment according to claim 6, characterized in that: The calcination temperature includes 600° C. The calcination includes: heating the solid particles obtained by the drying process to 600° C. at a heating rate of 1-10° C. / min, and calcining for 3-6 hours to obtain the sodium-modified mesoporous aluminum.

8. The use of sodium-modified mesoporous aluminum in carbon tetrafluoride treatment according to claim 1, characterized in that: The input voltage of the plasma reactor for forming the low-temperature plasma field is 20-40 kV.

9. The use according to claim 1, characterized in that The oxygen concentration in the carbon tetrafluoride-containing flue gas is 5%-20%.

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