A method of decomposing carbon tetrafluoride

Abstract

The application provides a method for decomposing carbon tetrafluoride, comprising the following steps: flowing the carbon tetrafluoride-containing gas to be treated through mesoporous aluminum in a low-temperature plasma field for decomposition treatment; wherein the oxygen concentration in the carbon tetrafluoride-containing gas is less than or equal to 10%; the mesoporous aluminum is arranged in a discharge area of the low-temperature plasma field; and the mesoporous aluminum is an amorphous aluminum isopropoxide material with a wormhole structure on the surface. The application can solve the problem of low efficiency of decomposing carbon tetrafluoride in the prior art, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the application of catalysts for the decomposition of carbon tetrachloride, and more particularly to a method for the decomposition of carbon tetrafluoride. Background Technology

[0002] Carbon tetrafluoride (CF4) is a typical strong greenhouse gas. The CF bond energy in the CF4 molecule is as high as 543±4 kJ / mol, giving it extremely strong chemical stability and long-wave radiation absorption capacity. The global warming potential (GWP) of CF4 is 6500 times that of CO2, and its atmospheric lifetime is as long as 50,000 years.

[0003] Currently, there are various methods for CF4 decomposition, including thermocatalysis and plasma. Due to the high stability of CF4, thermal decomposition alone requires heating to 1000 degrees Celsius. While introducing catalysts can effectively lower the decomposition temperature, existing catalysts still require temperatures above 600 degrees Celsius to maintain efficient CF4 degradation. Low-temperature plasma is a flue gas pollution purification technology that has attracted much attention in recent years. Its advantage lies in achieving the decomposition and purification of flue gas pollutants at room temperature. Studies have shown that plasma can effectively decompose CF4 into various products by exciting gas molecules to generate active particles. However, since plasma decomposition of CF4 is achieved through energy excitation, high energy consumption is inevitable. Furthermore, corrosive decomposition products such as HF and F2 can corrode discharge equipment, posing serious safety hazards. The synergistic effect between catalysts and plasma can improve the efficiency of plasma chemical processes. The plasma discharge process excites gas molecules to generate a large number of high-energy particles, enhancing the chemical reaction between the gas and the catalyst, thereby reducing energy consumption and improving efficiency. The aforementioned patent ZL 20221 1529433.7 reported a method for the catalytic decomposition of CF4 using carbon-supported alumina as a catalyst in conjunction with low-temperature plasma. However, this catalyst suffers from low decomposition efficiency due to its small pore size and limited number of surface active sites. This invention provides a method for the highly efficient catalytic decomposition of CF4 using hydroxyl-rich mesoporous aluminum combined with plasma. This hydroxyl-rich mesoporous aluminum possesses advantages such as abundant surface hydroxyl groups and a well-developed pore structure, thereby enhancing the decomposition reaction between CF4 and the catalyst surface. Summary of the Invention

[0004] The main objective of this invention is to provide a method for decomposing carbon tetrafluoride, aiming to solve the problem of low efficiency in decomposing carbon tetrafluoride using existing technologies.

[0005] To achieve the above objectives, the present invention provides a method for decomposing carbon tetrafluoride, comprising the steps of:

[0006] The gas containing carbon tetrafluoride to be treated is decomposed by flowing through mesoporous aluminum in a low-temperature plasma field.

[0007] Wherein, the oxygen concentration in the carbon tetrafluoride-containing gas is ≤10%;

[0008] The mesoporous aluminum is placed in the discharge region of the low-temperature plasma field;

[0009] The mesoporous aluminum is an amorphous aluminum isopropoxide material with a wormhole-like structure on its surface.

[0010] Furthermore, the flow rate of the carbon tetrafluoride-containing gas in the low-temperature plasma field is 10–50 mL / min.

[0011] Furthermore, the input voltage of the plasma reactor that forms the low-temperature plasma field is 10–60 kV.

[0012] Furthermore, the specific surface area of ​​the mesoporous aluminum is ≥300m². 2 / g; the pore volume of the mesoporous aluminum is ≥0.5cm³. 3 / g; the pore size of the mesoporous aluminum is 2-50nm.

[0013] Furthermore, the mesoporous aluminum is obtained by means of:

[0014] A mixture was prepared by mixing polyether solution, nitric acid, and aluminum isopropoxide.

[0015] The ratio of the added polyether P123, the nitric acid, and the aluminum isopropoxide is 1g:1.5ml:2-4g, wherein the concentration of the nitric acid is 65%.

[0016] The mixture was subjected to stirring, drying and calcination in sequence to obtain mesoporous aluminum;

[0017] The calcination temperature is 600–800°C.

[0018] Furthermore, the polyether solution is obtained by dissolving 1g of polyether P123 in 20mL of ethanol.

[0019] Furthermore, the stirring treatment lasts for 4 to 8 hours.

[0020] Furthermore, the drying temperature is 50–80°C; the drying time is 2–4 days.

[0021] Furthermore, the calcination treatment lasts for 3 to 8 hours.

[0022] Furthermore, the heating rate of the calcination treatment is 2°C / min.

[0023] The beneficial effects achieved by this invention are as follows:

[0024] The method for decomposing carbon tetrafluoride provided by this invention involves passing the carbon tetrafluoride-containing gas (oxygen content ≤10%) to be treated through mesoporous aluminum (an amorphous aluminum isopropoxide material with a wormhole-like surface structure) in a low-temperature plasma field through a discharge region of the low-temperature plasma field for decomposition treatment. Using this method, the decomposition efficiency of carbon tetrafluoride can reach 99%; moreover, the operation is simple and has broad application prospects. 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 the structures shown in these drawings without creative effort.

[0026] Figure 1 The effect of mesoporous aluminum synthesized under different aluminum sources on CF4 decomposition efficiency in Example 2 of this invention;

[0027] Figure 2 The effect of mesoporous aluminum synthesized at different calcination temperatures on the decomposition efficiency of CF4 in Example 3 of this invention;

[0028] Figure 3 This is a comparison of the decomposition efficiency of CF4 by mesoporous aluminum and commercial Al2O3 coupled plasma in Example 4 of the present invention.

[0029] Figure 4 This is a comparison of the decomposition efficiency of CF4 by mesoporous aluminum coupled plasma at different flow rates in Example 5 of the present invention.

[0030] Figure 5 This is a comparison of the plasma decomposition efficiency of CF4 at different flow rates in Embodiment 6 of the present invention;

[0031] Figure 6 This is a schematic diagram illustrating the effect of oxygen-containing flue gas on CF4 decomposition performance in Example 7 of the present invention;

[0032] Figure 7 (a) is a SEM image of the mesoporous aluminum before the reaction in Example 8 of the present invention; Figure 7 (b) is a SEM image of the mesoporous aluminum after reaction in Example 8 of the present invention;

[0033] Figure 8 This is the XPS full spectrum of the mesoporous aluminum before and after the reaction in Example 9 of the present invention;

[0034] Figure 9The mesoporous aluminum NH3-TPD before and after the reaction in Example 10 of this invention;

[0035] Figure 10 This invention relates to mesoporous aluminum and commercial Al2O3 NH3-TPD in Example 10 of this invention.

[0036] Figure 11 (a) Infrared spectroscopy of pyridine adsorption before reaction in mesoporous aluminum in Example 11 of the present invention; Figure 11 (b) is the infrared image of pyridine adsorption after reaction with mesoporous aluminum in Example 11 of the present invention;

[0037] Figure 12 (a) is mesoporous aluminum and commercial Al2O3CO2-TPD as shown in Example 12 of the present invention; Figure 12 (b) is the CO2-TPD of mesoporous aluminum before and after the reaction in Example 11 of the present invention;

[0038] Figure 13 (a) is the Al 2p XPS spectrum of mesoporous aluminum in Example 13 of the present invention. Figure 13 (b) is the C1s XPS spectrum of the interporous aluminum in Example 13 of the present invention; Figure 13 (c) is the O1s XPS spectrum of the interporous aluminum in Example 13 of the present invention; Figure 13 (d) is the F1s XPS spectrum of the interporous aluminum in Example 13 of the present invention;

[0039] Figure 14 (a) is a SEM image of the perforated aluminum in Example 9 of the present invention; Figure 14 (b) is the XRD diffraction pattern of the porous aluminum in Example 9 of the present invention; Figure 14 (c) is a TEM image of the perforated aluminum in Example 9 of the present invention; Figure 14 (d) Selected area electron diffraction of the porous aluminum in Example 9 of the present invention;

[0040] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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.

[0042] It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of this invention is for describing specific implementations and not for limiting the scope of protection of this invention.

[0043] Unless otherwise defined, all technical and scientific terms used in this invention are consistent with the prior art known to those skilled in the art and the description of this invention. This invention can also be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention. It should be understood by those skilled in the art that, as an explanation of this application, without affecting the actual understanding of the technical solutions of this application, "Intensity (au)" can represent strength, "Stress" can represent stress, "Strain" can represent strain, "Grain size" can represent grain size, and "Frequency" can represent frequency.

[0044] When numerical ranges are given in the examples, it should be understood that, unless otherwise stated in the invention, both endpoints of each range and any value between the two endpoints may be used. Test methods in the following examples that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers. Unless otherwise specified, all materials or reagents required in the following examples are commercially available.

[0045] To address the problems of low efficiency and complex processes in the decomposition of carbon tetrafluoride using existing technologies, this invention provides a method for decomposing carbon tetrafluoride, comprising the following steps:

[0046] The carbon tetrafluoride-containing gas to be treated is decomposed by flowing through mesoporous aluminum in a low-temperature plasma field.

[0047] The oxygen concentration in the carbon tetrafluoride-containing gas is ≤10%. During the experiment, it was found that oxygen itself decomposes in the plasma field, consuming the plasma's energy and thus competing with CF4 decomposition. Under oxygen-free conditions, the mesoporous aluminum coupled with plasma exhibits the highest CF4 decomposition efficiency. Introducing O2 significantly reduces this efficiency, and the oxygen concentration in the carbon tetrafluoride-containing gas should not exceed 10%. Because O2 is electronegative, when its concentration in the reaction system reaches a certain level, it competes with CF4, reducing the energy the plasma exerts on CF4 and thus lowering the decomposition efficiency. Furthermore, the O2 introduced under plasma reacts with the mesoporous aluminum, altering the active sites on the surface and further decreasing the decomposition efficiency. Preferably, the presence of oxygen in the carbon tetrafluoride-containing gas, with a concentration not exceeding 10%, helps reduce the deposition of carbon (C) from CF4 decomposition on the mesoporous aluminum surface, preventing pore blockage and promoting the oxidative conversion of byproducts CH2F2 and CO, resulting in more CO2 production.

[0048] Mesoporous aluminum is placed in the discharge region of a low-temperature plasma field.

[0049] Mesoporous aluminum is an amorphous aluminum isopropoxide material with a wormhole-like surface structure. Specifically, mesoporous aluminum is prepared using the sol-gel method. Experimental studies have found that the surface of mesoporous aluminum prepared using aluminum isopropoxide contains more hydroxyl groups. That is, before the reaction, the Al on the surface of mesoporous aluminum is mainly in the form of Al-OH. Under the action of -OH, F after the decomposition of CF4 combines with Al to form AlF3, while C after the decomposition of CF4 is deposited on the surface of mesoporous aluminum and combines with O sites to form CO.

[0050] Mesoporous aluminum surfaces also contain a higher content of strongly acidic sites, more weakly basic sites (Al-OH), and fewer strongly basic sites (O). 2- It contains active oxygen (such as glutaraldehyde), exhibiting higher CF4 catalytic activity. Experiments show that the strong acid sites in this mesoporous aluminum are mainly Lewis acids (L acids) and Brønsted acids (B acids), and the content of B acid sites on the surface of this mesoporous aluminum accounts for more than 50% of the total number of strong acid sites, indicating that they are important active sites for the CF4 decomposition reaction. At the same time, during the decomposition process, the weak basic sites on the surface of this mesoporous aluminum disappear and the strong basic sites increase, working together to promote the decomposition of CF4.

[0051] Furthermore, compared to mesoporous aluminum prepared using aluminum acetate and aluminum nitrate, it has a larger surface area and a more developed pore structure, which can significantly mitigate the adverse effects of C and F deposition on the surface of mesoporous aluminum during the decomposition of carbon tetrafluoride. This results in a significant improvement in the decomposition efficiency and service life of mesoporous aluminum for CF4 under the same conditions.

[0052] The method for decomposing carbon tetrafluoride provided by this invention involves passing the carbon tetrafluoride-containing gas (oxygen content ≤10%) to be treated through mesoporous aluminum (an amorphous aluminum isopropoxide material with a wormhole-like surface structure) in a low-temperature plasma field through a discharge region of the low-temperature plasma field for decomposition treatment. Using this method, the decomposition efficiency of carbon tetrafluoride can reach 99%; moreover, the operation is simple and has broad application prospects.

[0053] Furthermore, the flow rate of carbon tetrafluoride-containing gas in the low-temperature plasma field is 10–50 mL / min. Specifically, when the flow rate of carbon tetrafluoride-containing gas in the low-temperature plasma field is 10–50 mL / min, the decomposition efficiency of carbon tetrafluoride can be stably maintained at 70% or higher. During the decomposition process, the flow rate of carbon tetrafluoride-containing gas should not be too high; firstly, with an increased flue gas flow rate, the amount of CF4 to be decomposed by mesoporous aluminum per unit time will increase significantly. Therefore, under the same time period and high flue gas flow rate conditions, more C and F will be covered and deposited on the surface of mesoporous aluminum. In addition, at a high flow rate, the energy of the plasma field will be consumed by more CF4 molecules, thereby reducing the activation energy obtained by a single CF4 molecule and reducing the decomposition efficiency.

[0054] Furthermore, the input voltage of the plasma reactor that forms the low-temperature plasma field is 10–60 kV.

[0055] For example, the input voltage of the plasma reactor that forms the low-temperature plasma field can be 20 to 40 kV.

[0056] Furthermore, the specific surface area of ​​mesoporous aluminum is ≥300 m². 2 / g; pore volume of mesoporous aluminum ≥0.5cm³ 3 / g; the pore size of mesoporous aluminum is 2-50nm.

[0057] Furthermore, mesoporous aluminum can be obtained through the following methods:

[0058] A mixture is obtained by mixing polyether solution, nitric acid, and aluminum isopropoxide.

[0059] The mixture was subjected to stirring, drying and calcination in sequence to obtain mesoporous aluminum.

[0060] The calcination temperature is 600–800℃.

[0061] Furthermore, the polyether solution is obtained by dissolving 1g of polyether P123 in 20mL of ethanol.

[0062] Furthermore, the stirring treatment lasts for 4 to 8 hours.

[0063] Furthermore, the drying temperature is 50–80°C; the drying time is 2–4 days.

[0064] Furthermore, the calcination treatment lasts for 3 to 8 hours.

[0065] Furthermore, the heating rate of the calcination treatment is 2℃ / min.

[0066] To further illustrate the present invention, the following examples are provided:

[0067] Example 1

[0068] Preparation of mesoporous aluminum

[0069] 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 about 6 hours. Then, it was placed in a drying oven at 60 °C and heated for 2 days to evaporate the solution. Finally, the obtained solid particles were calcined at 600 °C for 5 hours at a heating rate of 2 °C / min to obtain mesoporous aluminum.

[0070] In addition, aluminum acetate and aluminum nitrate were used as aluminum sources to prepare mesoporous aluminum acetate and mesoporous aluminum nitrate using the same method, respectively, to compare the catalytic effect of mesoporous aluminum with different aluminum sources.

[0071] Example 2

[0072] The three mesoporous aluminum materials prepared in Example 1, namely mesoporous aluminum (illustrated as aluminum isopropoxide), aluminum acetate mesoporous aluminum (illustrated as aluminum nitrate), and aluminum nitrate mesoporous aluminum (illustrated as aluminum nitrate), were decomposed under a flue gas (containing carbon tetrafluoride gas) flow rate of 20 mL / min. Specifically, the decomposition process did not involve a low-temperature plasma field; only the flue gas flowed through the three mesoporous aluminum materials at a flow rate of 20 mL / min. The decomposition efficiency was as follows: Figure 1 As shown.

[0073] from Figure 1 The results show that mesoporous aluminum has a decomposition efficiency of up to 82% for CF4, which is 25% higher than that of aluminum acetate mesoporous aluminum, while the decomposition efficiency of aluminum nitrate mesoporous aluminum for CF4 is only 38%. This suggests that the presence of more hydroxyl groups on the surface of mesoporous aluminum may play a role in its higher efficiency in decomposing CF4.

[0074] Example 3

[0075] Compared to the mesoporous aluminum preparation process in Example 1, the calcination temperature was changed to 300℃ and 800℃ respectively to obtain mesoporous aluminum at -300℃ (300℃ shown in the figure) and mesoporous aluminum at -800℃ (800℃ shown in the figure).

[0076] Carbon tetrafluoride gas was flowed at a flow rate of 20 mL / min through mesoporous aluminum at -300℃ (illustrated as 300℃), mesoporous aluminum at -800℃ (illustrated as 800℃), and mesoporous aluminum prepared in Example 1 at 600℃ to decompose CF4. Specific decomposition efficiencies are shown below. Figure 2 As shown.

[0077] from Figure 2 As can be seen, at a calcination temperature of 300℃, the decomposition efficiency of mesoporous aluminum for CF4 is relatively low, at 57%; when the calcination temperature is increased to 600℃, the decomposition efficiency of mesoporous aluminum for CF4 increases to 82%; further increasing the calcination temperature to 800℃, the decomposition efficiency of mesoporous aluminum for CF4 does not change significantly and remains at a relatively high level. Therefore, the optimal calcination temperature for the mesoporous aluminum of this invention is 600℃.

[0078] Example 4

[0079] Comparative experiments on the decomposition of carbon tetrafluoride were conducted using mesoporous aluminum prepared in Example 1, commercial Al2O3, and a plasma reactor without catalytic material (blank control group; the figure shows a single plasma). All three were coupled with a plasma reactor with an input voltage of 25V.

[0080] A 10% concentration of carbon tetrafluoride gas was flowed at a flow rate of 10 mL / min through a low-temperature plasma field formed by a plasma reactor with an input voltage of 25 V. The resulting materials were mesoporous aluminum (shown in the figure), commercial Al2O3 (shown in the figure), and a non-catalyst control group (shown in the figure, plasma alone). The carbon tetrafluoride decomposition process was performed, and the decomposition efficiency was recorded from 0 to 600 min. Details are as follows: Figure 3 As shown.

[0081] according to Figure 3 As shown, the decomposition efficiency of mesoporous aluminum on CF4 rapidly increased to 85% within the initial 200 min, and then slowly increased to a peak of approximately 99% after about 400 min. Under the same conditions, the peak decomposition efficiency of commercial Al2O3 on CF4 was only 74%, and the decomposition efficiency dropped below 50% after 300 min, which was comparable to the decomposition efficiency of plasma alone on CF4, indicating that commercial Al2O3 had already been deactivated at this point.

[0082] Example 5

[0083] Mesoporous aluminum prepared in Example 1 (flow rates of 10 mL / min, 20 mL / min, and 50 mL / min, respectively) was passed through a low-temperature plasma field formed by a plasma reactor with an input voltage of 25 V for carbon tetrafluoride decomposition treatment. The decomposition efficiency was recorded from 0 to 400 min. Figure 4 As shown.

[0084] from Figure 4 As can be seen, when the flue gas flow rate is 10 mL / min, the mesoporous aluminum achieves a maximum decomposition efficiency of 99% for CF4. When the flue gas flow rate is increased to 20 mL / min, the maximum decomposition efficiency of mesoporous aluminum for CF4 decreases to 82%, and when the flue gas flow rate is further increased to 50 mL / min, the decomposition efficiency drops to 70%. The experimental results show that the decomposition efficiency of CF4 decreases with increasing flue gas flow rate.

[0085] This indicates that as the flue gas flow rate increases, the amount of CF4 that the catalyst decomposes per unit time will increase significantly. Therefore, under the same time period and high flue gas flow rate conditions, more C and F will be covered and deposited on the catalyst surface.

[0086] Mesoporous aluminum prepared using aluminum isopropoxide as the aluminum source at a calcination temperature of 600℃ exhibits the best catalytic effect. The highest decomposition efficiency of CF4 by mesoporous aluminum coupled with plasma reaches 99%, which is 25% higher than that of commercial Al2O3 aluminum. Increasing the flux results in more CF4 molecules consuming the energy of the plasma field, thus reducing the activation energy of individual CF4 molecules and decreasing the decomposition efficiency.

[0087] Example 6

[0088] Compared to Example 5, mesoporous aluminum was not incorporated into the low-temperature plasma field. Specifically, carbon tetrafluoride-containing gas with flow rates of 10 mL / min, 20 mL / min, and 50 mL / min was passed through a low-temperature plasma field formed by a plasma reactor with an input voltage of 25 V (the figures show 10% CF4 at 10 mL / min, 10% CF4 at 20 mL / min, and 10% CF4 at 50 mL / min, respectively), for carbon tetrafluoride decomposition treatment. The decomposition efficiency was recorded from 0 to 150 minutes. (See details below.) Figure 5 As shown.

[0089] from Figure 5 As can be seen, the decomposition efficiency of CF4 under plasma alone also decreases with increasing flue gas flow rate. When the flue gas flow rate is 10 mL / min, the decomposition efficiency of CF4 stabilizes at about 50%; while when the flue gas flow rate is increased to 50 mL / min, the stable decomposition efficiency of CF4 decreases to about 30%.

[0090] Combination Figure 4 and Figure 5 The reason for this is that as the flue gas flow rate increases, the amount of CF4 to be decomposed by mesoporous aluminum per unit time increases significantly. Therefore, under the same flue gas flow rate conditions, more C and F will be covered and deposited on the surface of mesoporous aluminum. In addition, under high flow rates, the energy of the plasma field will be consumed by more CF4 molecules, thereby reducing the activation energy of a single CF4 molecule and decreasing the decomposition efficiency.

[0091] Example 7

[0092] The effect of O2 on CF4 decomposition efficiency was studied under conditions of 10% O2 concentration and 20 mL / min flue gas flow rate. Figure 6 As shown, under anaerobic conditions, a carbon tetrafluoride-containing gas with a flow rate of 20 mL / min flows through a low-temperature plasma field formed by a plasma reactor with an input voltage of 25 V. The decomposition efficiency of CF4 by the plasma alone is 38%. After introducing O2 with a concentration of 10%, the decomposition efficiency of CF4 drops to 34%, indicating that oxygen itself decomposes in the plasma field and consumes the energy of the plasma field, thus competing with the decomposition of CF4.

[0093] Under anaerobic conditions, the mesoporous aluminum prepared in Example 1, with a flue gas flow rate of 20 mL / min containing carbon tetrafluoride flowing through a low-temperature plasma field formed by a plasma reactor with an input voltage of 25 V, exhibited a maximum CF4 decomposition efficiency of 82%. However, the efficiency dropped to a maximum of 65% after introducing 10% O2. Because O2 is electronegative, when its concentration in the reaction system reaches a certain level, it competes with CF4, reducing the energy of the plasma on CF4 and thus lowering the decomposition efficiency. Furthermore, the O2 introduced under plasma conditions reacts with the mesoporous aluminum, altering the active sites on the surface and further reducing its CF4 decomposition efficiency.

[0094] Example 8

[0095] The morphological changes of mesoporous aluminum before and after the reaction in Example 7, under the conditions of 10% oxygen concentration and 20 ml / min flue gas flow rate, were analyzed using SEM. Figure 7 As shown, where Figure 7 (a) is a SEM image of mesoporous aluminum before the reaction. Figure 7 (b) is a SEM image of the mesoporous aluminum after the reaction. It can be seen that the surface of the mesoporous aluminum had a distinct pore structure before the reaction, while after the reaction, the pore structure disappeared, forming a dense layer. This indicates that the CF4 decomposition reaction has a significant impact on the morphology of the mesoporous aluminum. CF4 decomposition produces C and F deposits on the surface of the mesoporous aluminum, leading to pore blockage. Simultaneously, F may also corrode the surface of the mesoporous aluminum, thus altering its morphology.

[0096] Example 9

[0097] The surface elemental composition changes of mesoporous aluminum before and after the reaction were analyzed using SEM in Example 7, under the conditions of 10% oxygen concentration and 20 ml / min flue gas flow rate. Figure 8 As shown in the figure, before the reaction, mesoporous aluminum exhibits characteristic peaks belonging to Al 2p and O 1s at 76.51 eV and 533.14 eV, respectively. After the reaction, the intensity of the O 1s characteristic peak of mesoporous aluminum is significantly weakened, and a characteristic peak belonging to F 1s appears at 687.08 eV.

[0098] After the CF4 decomposition reaction, the Al and O content on the surface of mesoporous aluminum decreased by 8.8% and 29.1%, respectively, indicating that both elements may have participated in the CF4 decomposition reaction. Before the reaction, the carbon content on the surface of mesoporous aluminum was 20.66%, and after the reaction, the carbon content increased significantly to 50.29%, with the F content reaching as high as 10.07%.

[0099] The results confirmed that CF4 decomposition produces a large amount of C and F elements deposited on the surface of mesoporous aluminum, which may be an important reason for the disappearance of the pore structure.

[0100] Table 1 shows the changes in elemental content on the surface of mesoporous aluminum before and after the reaction.

[0101] Table 1 Comparison of elemental contents of mesoporous aluminum before and after reaction

[0102]

[0103] Example 10

[0104] The surface elemental composition changes of mesoporous aluminum before and after the reaction were analyzed using NH3-TPD in Example 7, under conditions of 10% oxygen concentration and 20 ml / min flue gas flow rate. Figure 9 As shown in the figure, before the reaction, mesoporous aluminum exhibits a characteristic peak at 300-500℃, corresponding to strongly acidic sites, with a content of 1.79 mmol / g. After the reaction, the content of strongly acidic sites on the surface of mesoporous aluminum decreases to 1.11 mmol / g, and a new characteristic peak belonging to weakly acidic sites appears at 100℃, with a content of 0.35 mmol / g. The results indicate that strongly acidic sites participate in the CF4 decomposition reaction.

[0105] This embodiment also performs NH3-TPD testing on the commercial alumina in Example 4, such as... Figure 10As shown, compared to mesoporous alumina, commercial alumina exhibits a higher NH3 desorption peak at a higher temperature during NH3-TPD testing, while its strong acid site content is 1.54 mmol / g, significantly lower than that of mesoporous alumina. Mesoporous alumina contains a higher concentration of strong acids on its surface, thus exhibiting higher CF4 catalytic activity.

[0106] Example 11

[0107] The influence of the types of acidic sites on the surface of mesoporous aluminum on CF4 decomposition was investigated. Pyridine-FTIR was used to analyze the mesoporous aluminum before and after the reaction in Example 7, under conditions of 10% oxygen concentration and 20 ml / min flue gas flow rate. Figure 11 As shown, where, Figure 11 (a) is the pyridine adsorption reaction of infrared mesoporous aluminum before the reaction. Figure 11 (b) After the pyridine adsorption reaction of mesoporous aluminum in infrared light. The acidic sites on the surface of mesoporous aluminum can be divided into Lewis acids (L acids) and Brønsted acids (B acids). Among them, the substances that can accept electron pairs are Lewis acids, and the substances that can donate protons are B acids.

[0108] First, the types and contents of acidic sites in mesoporous aluminum were analyzed at temperatures of 150℃, 200℃, and 350℃. Its Py-FTIR spectrum showed six distinct characteristic peaks, located at 1450 cm⁻¹. -1 1490cm -1 1540cm -1 1577cm -1 1594cm -1 and 1612cm -1 Located at 1440-1460cm -1 The characteristic peak between these two points corresponds to L acid, located at 1490 cm⁻¹. -1 The characteristic peaks at 1530-1550 cm⁻¹ correspond to L and Brønsted acids, respectively. -1 The characteristic peaks between these two values ​​correspond to Brønsted acid and are located at 1577-1620 cm⁻¹. -1 The characteristic peaks between them correspond to L acid.

[0109] The contents of L-acid and Brønsted acid are shown in Table 2. The acid content measured at 150℃ is the total acid content, and the acid content measured at 350℃ is the strong acid content.

[0110] The results showed that the proportion of Brønsted (B) acid sites on the surface of mesoporous aluminum exceeded 50% of the total strong acid sites, indicating that they are important active sites for the CF4 decomposition reaction. Before the reaction, the content of Lewis acid (L acid) on the surface of mesoporous aluminum was 123.78 μmol / g, and the content of Brønsted (B acid) was 56.42 μmol / g. After the reaction, the content of Lewis acid increased to 243.21 μmol / g, while the content of Brønsted (B acid) decreased to 3.75 μmol / g, further demonstrating that Brønsted (B) acid sites are important active sites participating in the CF4 reaction.

[0111] Table 2. Contents of mesoporous aluminic acid (L-acid) and Br-acid before and after the reaction.

[0112]

[0113]

[0114] Example 12

[0115] The changes in surface alkaline sites of mesoporous aluminum before and after the reaction were analyzed using CO2-TPD in Example 7 under the conditions of 10% oxygen concentration and 20 ml / min flue gas flow rate. Figure 12 As shown, where Figure 12 (a) CO2-TPD test results for mesoporous aluminum and commercial Al2O3; Figure 12 (b) shows the CO2-TPD test results before and after the reaction of mesoporous aluminum.

[0116] Mesoporous aluminum exhibits CO2 desorption peaks at 100℃ and 400℃, corresponding to weakly basic and strongly basic sites, respectively. The content of weakly basic sites is 0.85 mmol / g, while the content of strongly basic sites is 0.5 mmol / g. After the reaction, the weakly basic sites on the mesoporous aluminum disappear, while the content of strongly basic sites increases from 0.5 mmol / g to 1.76 mmol / g, indicating that the weakly basic sites on the surface of mesoporous aluminum participate in the CF4 decomposition reaction. Commercial Al2O3 also exhibits both weakly basic and strongly basic sites on its surface, with contents of 0.39 mmol / g and 1.32 mmol / g, respectively. The content of weakly basic sites is 0.46 mmol / g lower than that of mesoporous aluminum, while the content of strongly basic sites is 0.82 mmol / g higher. Clearly, the greater number of weakly basic sites and fewer strongly basic sites on the surface of mesoporous aluminum give it significantly superior CF4 decomposition performance compared to commercial Al2O3.

[0117] The acidic sites on the surface of alumina are usually Al 3+ and Al-OH, where Al 3+ It is an L-acid, and Al-OH is a Brønsted acid; it also typically has two basic sites: a hydroxyl ion site (Al-OH) and an oxygen ion site (O). 2- ), O 2- The basicity of Al-OH is stronger than that of Al-OH. Therefore, the weakly basic sites on the surface of mesoporous aluminum are Al-OH, while the strongly basic sites are O. 2- Active oxygen species are present. Al-OH can play a dual role as both an acidic and basic site, when the reaction process only provides H+. + When the alumina is acidic, it becomes a basic site when it donates -OH. The acid-base site analysis results show that the mesoporous aluminum surface contains a higher number of hydroxyl groups and weakly basic sites. Among them, the aluminum hydroxyl group is both a basic site and may donate a proton during the CF4 decomposition reaction, playing a dual role as a basic site and a Brønsted acid.

[0118] Example 13

[0119] The changes in surface alkaline sites of mesoporous aluminum before and after the reaction were analyzed using CO2-TPD in Example 7 under the conditions of 10% oxygen concentration and 20 ml / min flue gas flow rate. Figure 13 As shown, where, Figure 13 (a) is the 2p orbital electron energy spectrum of aluminum; Figure 13 (b) Electron spectrum of carbon's 1s orbital; Figure 13 (c) 1s orbital electron spectrum of carbon Figure 13 (d) Electron spectrum of fluorine in 1s orbital.

[0120] Before the reaction, the main peak of the Al 2p orbital was located at 74.17 eV, while after the reaction it shifted to 76.25 eV. This shift of the Al 2p characteristic peak to the higher binding energy region indicates that Al participated in the CF4 decomposition reaction, and that the charge density decreased during this process. Before the reaction, the Al morphology on the mesoporous aluminum surface was mainly Al-OH, but after the reaction it transformed into AlF3. Figure 13 As shown in (b), the characteristic peak of F1s on the mesoporous aluminum surface after the reaction is located at 686.67 eV, corresponding to AlF3, further indicating that F after CF4 decomposition combines with Al to form AlF3. The O1s spectra before and after the reaction are shown below. Figure 13 As shown in (c), the characteristic peaks at 530.77 eV and 531.89 eV before the reaction correspond to O, respectively. ads The O1s group and -OH group accounted for 44% and 56% respectively. After the reaction, O1s shifted to higher binding energies and showed a characteristic peak of CO at 534.73 eV, accounting for 8.38%. The -OH content decreased to 41.65%. ads The content increased to 50.03%, indicating that -OH participated in the decomposition of CF4 and its conversion to CO. Before the reaction, C1s had three characteristic peaks at 284.71 eV, 285.54 eV, and 289.29 eV, corresponding to CCC, CO, and OC=O, respectively. Figure 13 (d). The CO content increased from 27.3% to 49.1% after the reaction, indicating that the C from the decomposition of CF4 deposits on the catalyst surface and combines with O sites to form CO.

[0121] The XPS bond valence content analysis is shown in Table 3.

[0122] Table 3 XPS Bond Valence Content Analysis

[0123]

[0124] Mesoporous aluminum has a higher content of acidic and basic sites on its surface. The weakly basic sites are Al-OH, and the strongly basic sites are O. 2-Active oxygen is present. After the reaction, Al-OH on the surface of the mesoporous aluminum participates in the decomposition of CF4, transforming into C and AlF3, which are deposited on the catalyst surface, leading to pore blockage and a decrease in CF4 decomposition efficiency. Introducing O2 promotes the oxidative conversion of byproducts CH2F2 and CO, generating more CO2.

[0125] Example 14

[0126] The morphological characteristics of the mesoporous aluminum obtained in Example 1 were studied using SEM, such as... Figure 14 As shown, the mesoporous aluminum surface exhibits clearly defined macropores, further indicating that mesoporous aluminum is a porous material. The phase structure of the mesoporous aluminum was analyzed using XRD, as shown below. Figure 14 As shown in (b), the XRD pattern of mesoporous aluminum shows no obvious characteristic peaks, indicating that the material has an amorphous morphology. Figure 14 (c) is a TEM image of mesoporous aluminum, showing that it exhibits a typical wormhole-like structure and that no obvious diffraction rings are present. Figure 14 (d) proves that mesoporous aluminum is in an amorphous state and contains abundant pore structures.

[0127] Table 4 Comparison of specific surface area, pore volume, and pore size of catalysts

[0128]

[0129] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for decomposing carbon tetrafluoride, characterized in that, Including the following steps: The gas containing carbon tetrafluoride to be treated is decomposed by flowing through mesoporous aluminum in a low-temperature plasma field. Wherein, the oxygen concentration in the carbon tetrafluoride-containing gas is ≤10%; The mesoporous aluminum is placed in the discharge region of the low-temperature plasma field; The mesoporous aluminum is an amorphous mesoporous aluminum material prepared from aluminum isopropoxide with a wormhole-like structure on its surface.

2. The method for decomposing carbon tetrafluoride according to claim 1, characterized in that, The flow rate of the carbon tetrafluoride-containing gas in the low-temperature plasma field is 10~50 mL / min.

3. The method for decomposing carbon tetrafluoride according to claim 1, characterized in that, The plasma reactor that forms the low-temperature plasma field has an input voltage of 10~60V.

4. The method for decomposing carbon tetrafluoride according to claim 1, characterized in that, The specific surface area of ​​the mesoporous aluminum is ≥300m². 2 / g; the pore volume of the mesoporous aluminum is ≥0.5cm³. 3 / g; the pore size of the mesoporous aluminum is 2~50nm.

5. The method for decomposing carbon tetrafluoride according to any one of claims 1 to 4, characterized in that, The mesoporous aluminum is obtained by means of: A mixture of polyether solution, nitric acid, and aluminum isopropoxide is prepared by mixing the polyether solution, nitric acid, and aluminum isopropoxide to obtain a mixture; the polyether solution is obtained by dissolving 1g of polyether P123 in 20mL of ethanol. The ratio of the added polyether P123, the nitric acid, and the aluminum isopropoxide is 1g:1.5ml:2~4g, wherein the concentration of the nitric acid is 65%. The mixture was subjected to stirring, drying and calcination in sequence to obtain mesoporous aluminum; The calcination temperature is 600~800℃.

6. The method for decomposing carbon tetrafluoride according to claim 5, characterized in that, The stirring process lasts for 4 to 8 hours.

7. The method for decomposing carbon tetrafluoride according to claim 5, characterized in that, The drying temperature is 50~80℃; the drying time is 2~4 days.

8. The method for decomposing carbon tetrafluoride according to claim 5, characterized in that, The calcination treatment lasts for 3 to 8 hours.

9. The method for decomposing carbon tetrafluoride according to claim 5, characterized in that, The heating rate of the calcination treatment is 2℃ / min.

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