Preparation method of plasma catalyst and application of plasma catalyst in degradation of low-concentration dimethyl sulfide

Abstract

The invention discloses a plasma catalyst, a preparation method thereof and application of the plasma catalyst in degradation of dimethyl sulfide by plasmas. The plasma catalyst comprises a manganese oxide carrier and Ag monoatoms loaded on the manganese oxide carrier; the manganese oxide carrier comprises rod-like crystalline manganese dioxide and amorphous manganese oxide wrapping the outer layer of the crystalline manganese dioxide. The preparation method comprises the following steps: 1) uniformly dispersing rod-like crystalline manganese dioxide in a mixed solution B of potassium permanganate and manganese sulfate, stirring for reaction, then carrying out solid-liquid separation, taking a solid, washing and drying to obtain a manganese oxide carrier; and 2) dispersing the manganese oxide carrier in deionized water, then adding a silver nitrate solution into the deionized water, uniformly mixing, then dropwise adding a hydrogen peroxide solution, stirring for reaction, then carrying out solid-liquid separation, taking a solid, washing, drying and calcining in a non-oxidizing atmosphere to obtain the plasma catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of gaseous pollutant treatment, and particularly relates to a plasma catalyst, a preparation method thereof, and an application thereof in the plasma degradation of dimethyl sulfide (DMS). Background Art

[0002] The low-temperature plasma technology, with its unique electron temperature characteristics (1 - 20 eV), shows remarkable potential in the field of gas treatment. This technology can promote the ionization and dissociation of gas molecules and atoms, generating free radicals and other active particles, which can initiate a series of non-traditional chemical reactions to effectively decompose and remove pollutants. The low-temperature plasma technology has become an ideal choice for treating gaseous pollutants such as volatile organic compounds (VOCs) due to its advantages of simple operation, short treatment time, high cost-effectiveness, and small space occupation, and is widely favored by researchers at home and abroad.

[0003] In order to improve the treatment efficiency and the selectivity of target products, and at the same time reduce the risk of secondary pollution, the low-temperature plasma technology is often used in combination with the catalytic technology. This combination utilizes the active particles generated by the low-temperature plasma to enhance the activity of the catalyst, improve the degradation efficiency of pollutants, and may reduce the deactivation rate of the catalyst. In recent years, significant progress has been made in the research on the synergistic effect of plasma and catalytic technology in the field of gaseous pollutant treatment.

[0004] Existing studies have shown that crystalline manganese oxide has excellent electrical conductivity and high redox performance, which has been verified in electrocatalytic and other reactions. Due to its irregular atomic arrangement and high density of defects, amorphous materials are more likely to generate oxygen vacancies, providing more reaction sites. By combining the advantages of amorphous and crystalline structures, it is expected to construct a catalyst with excellent synergistic effects in plasma catalytic reactions.

[0005] Through the above analysis, the following main problems exist in the prior art:

[0006] (1) There are high-energy electrons in the plasma system, but the general catalyst itself has weak electric field response ability, resulting in low discharge power and affecting the utilization of high-energy electrons;

[0007] (2) In the plasma system, the escape of excess ozone will cause secondary pollution;

[0008] (3) The existing catalysts lack the concept of multi-functional design, and the development of catalysts for sulfur-containing malodorous pollutants needs to be carried out urgently.

[0009] The patent specification with the publication number CN113559849A discloses a preparation method of an amorphous manganese oxide catalyst for catalytic decomposition of ozone. The patent specification with the publication number CN109772159A discloses an amorphous manganese oxide catalyst, its preparation method and application in catalytic decomposition of ozone. These patent technologies only involve ozone decomposition and do not involve the catalytic degradation of sulfur-containing malodorous pollutants. Summary of the Invention

[0010] The present invention provides a plasma catalyst, its preparation method and application in plasma degradation of methyl mercaptan.

[0011] [1] A plasma catalyst, comprising a manganese oxide support and Ag single atoms supported on the manganese oxide support;

[0012] The manganese oxide support includes rod-shaped crystalline manganese dioxide and amorphous manganese oxide wrapped around the outer layer of the crystalline manganese dioxide.

[0013] The inventors have studied and found that the core-shell structure of rod-shaped crystalline manganese dioxide wrapped with amorphous manganese oxide in the present invention can make the combination between amorphous manganese oxide and crystalline manganese dioxide more uniform and tight, with stronger interaction, and can simultaneously achieve the dual functions of electric field response and ozone decomposition, which is significantly better than other forms of combined loading.

[0014] For the plasma catalyst described above, the mass ratio of the Ag single atoms to the manganese oxide support can be 1:500 to 1200, preferably 1:700 to 1200, such as 1:900, 1:950, 1:1000, etc. When the plasma catalyst under the preferred conditions is used for plasma degradation of methyl mercaptan, it can exhibit high methyl mercaptan removal efficiency and low ozone concentration in the tail gas.

[0015] For the plasma catalyst described above, the mass ratio of the amorphous manganese oxide to the crystalline manganese dioxide can be 1:2 to 20, preferably 1:2 to 3, such as 1:2.5, etc. When the plasma catalyst under the preferred conditions is used for plasma degradation of methyl mercaptan, it can exhibit high methyl mercaptan removal efficiency and low ozone concentration in the tail gas.

[0016] [2] The preparation method of the plasma catalyst according to [1], comprising the steps:

[0017] 1) Uniformly disperse rod-shaped crystalline manganese dioxide in the mixed solution B of potassium permanganate and manganese sulfate, stir and react, then perform solid-liquid separation, take the solid, wash and dry to obtain the manganese oxide support;

[0018] 2) Disperse the manganese oxide support in deionized water, then add silver nitrate solution thereto, mix well and then dropwise add hydrogen peroxide solution, stir and react, then carry out solid-liquid separation, take the solid, wash and dry it, and calcine it in a non-oxidizing atmosphere to obtain the plasma catalyst.

[0019] The preparation method of the rod-shaped crystalline manganese dioxide may include: preparing a mixed solution A of potassium permanganate and manganese sulfate, and carrying out a hydrothermal reaction at 100-160 °C, preferably 110-150 °C, and further preferably 130-140 °C to obtain the rod-shaped crystalline manganese dioxide.

[0020] In the mixed solution A, the molar ratio of potassium permanganate to manganese sulfate may be 1-5:1, such as 2:1, etc.

[0021] In the preparation method of the rod-shaped crystalline manganese dioxide, the time of the hydrothermal reaction may be 6-24 hours, such as 12 hours, etc.

[0022] In the mixed solution B, the molar ratio of potassium permanganate to manganese sulfate may be 1-5:1, such as 2:1, etc.

[0023] In step 1), the mass ratio of the crystalline manganese dioxide to potassium permanganate in the mixed solution B may be (0.1-1):(0.2-0.3), preferably (0.3-0.8):(0.2-0.3), and further preferably (0.4-0.6):(0.2-0.3). When the plasma catalyst under the preferred conditions is used for plasma degradation of methyl mercaptan, it can show high methyl mercaptan removal efficiency and low ozone concentration in the tail gas.

[0024] In step 1), the temperature of the stirring reaction may be 15-40 °C, such as 30 °C, etc., and the time may be 4-8 hours, such as 6 hours, etc.

[0025] In step 2), the molar amount of silver nitrate in the added silver nitrate solution and the mass ratio of the manganese oxide support may be (1-20)×10 -3 mmol:1 g, preferably (5-15)×10 -3 mmol:1 g, and further preferably (8-12)×10 - 3 mmol:1 g. When the plasma catalyst under the preferred conditions is used for plasma degradation of methyl mercaptan, it can show high methyl mercaptan removal efficiency and low ozone concentration in the tail gas. When the added Ag content is too high, it will easily produce larger nanoparticles instead of single atoms, which is not conducive to the improvement of methyl mercaptan removal efficiency and the reduction of tail gas ozone concentration.

[0026] In step 2), the mass ratio of H2O2 in the dropwise added hydrogen peroxide solution to the molar amount of silver nitrate in the added silver nitrate solution may be 0.01-0.05 g:(1×10-3 ) mmol, such as 0.03 g:(1×10 -3 ) mmol, etc.

[0027] In step 2), calcination is carried out in a non-oxidizing atmosphere to avoid the oxidation of the surface amorphous manganese oxide. In step 2), the non-oxidizing atmosphere can be a nitrogen atmosphere and / or a noble gas atmosphere, etc.

[0028] In step 2), the calcination temperature can be 300-500 °C, such as 400 °C, etc.

[0029] In step 2), the calcination time can be 3-4 hours.

[0030] [3] The application of the plasma catalyst described in [1] in the plasma catalytic degradation of methyl mercaptan. The plasma catalyst is located in the discharge area where the plasma is generated in the plasma reactor or after the discharge area. A mixture of methyl mercaptan and an oxidizing gas passes through the discharge area or sequentially passes through the discharge area and the plasma catalyst. Under the combined action of the plasma and the plasma catalyst, methyl mercaptan is degraded.

[0031] In the above application, the oxidizing gas can include at least one of oxygen and ozone.

[0032] The plasma catalyst of the present invention can utilize ozone to degrade methyl mercaptan and reduce ozone escape.

[0033] In the above application, each part of the plasma catalyst of the present invention can play a functional role respectively. Ag single atoms can preferentially adsorb pollutant molecules such as methyl mercaptan. The high conductivity of crystalline manganese dioxide can effectively increase the electric field strength in the system. Amorphous manganese oxide can effectively utilize the excess ozone in the system to promote the deep oxidation of pollutants, and has an excellent synergistic effect.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] During the process of plasma catalytic degradation of the sulfur-containing malodorous pollutant methyl mercaptan by the plasma catalyst of the present invention, it can effectively improve the removal rate of pollutants, reduce energy consumption, and greatly inhibit ozone escape in the tail gas.

[0036] The plasma catalyst of the present invention is an Ag single atom-loaded crystalline@amorphous core-shell structure catalyst. This structure combines the dual advantages of the high electric field responsiveness of crystalline manganese dioxide and the high ozone utilization ability of amorphous manganese oxide, and optimizes the charge transfer between interfaces. The surface Ag single atoms and the abundant defects existing at the interface provide abundant adsorption sites, and at the same time promote the adsorption of sulfur-containing malodorous molecules and the utilization of ozone, realizing the efficient degradation of methyl mercaptan in the plasma catalytic system and the efficient utilization of ozone.

[0037] Compared with the plasma catalysts reported currently, the plasma catalyst provided by the present invention has significant advantages in the adsorption of sulfur-containing malodorous pollutants and the control of tail gas ozone, which mainly stems from the characteristics of Ag single atoms and the crystalline @ amorphous core-shell structure material, realizing excellent synergistic effects in the plasma catalytic system. Description of the Drawings

[0038] Figure 1 In part (a) of [], it is the scanning electron microscope (SEM) photograph of Ag / MnO2@MnO in Example 1 x and in part (b), it is the high-resolution transmission electron microscope (HRTEM) photograph of Ag / MnO2@MnO in Example 1 x .

[0039] Figure 2 It is the graph of the performance of crystalline MnO2 in Comparative Example 1 for the degradation of methyl mercaptan in the plasma catalytic system varying with the energy density, where: (a) is the removal rate of methyl mercaptan, and (b) is the tail gas ozone concentration.

[0040] Figure 3 It is the graph of the performance of amorphous manganese oxide in Comparative Example 2 for the degradation of methyl mercaptan in the plasma catalytic system varying with the energy density, where: (a) is the removal rate of methyl mercaptan, and (b) is the tail gas ozone concentration.

[0041] Figure 4 It is the graph of the performance of Ag / MnO2@MnO with different MnO2 addition amounts in Example 1 and Example 2 for the degradation of methyl mercaptan in the plasma catalytic system varying with the energy density, where: (a) is the removal rate of methyl mercaptan, and (b) is the tail gas ozone concentration. x

[0042] Figure 5 It is the graph of the performance of Ag / MnO2@MnO with different Ag addition amounts in Example 1 and Example 3 for the degradation of methyl mercaptan in the plasma catalytic system varying with the energy density, where: (a) is the removal rate of methyl mercaptan, and (b) is the tail gas ozone concentration. x

[0043] Figure 6 It is the graph of the performance of the plasma synergistic Ag / MnO2@MnO in Example 1 x and the performance of the separate plasma for the degradation of methyl mercaptan in Example 4 varying with the energy density, where (a) is the removal rate of methyl mercaptan, and (b) is the tail gas ozone concentration. Detailed Embodiments

[0044] The present invention will be further described below in conjunction with the drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0045] Example 1:

[0046] Preparation of crystalline manganese dioxide MnO₂: 50 mL of KMnO₄ solution (containing 0.316 g of KMnO₄) and 50 mL of MnSO₄ solution were mixed at a molar ratio of KMnO₄:MnSO₄ of 2:1 under vigorous stirring, followed by hydrothermal reaction and heating at 140 °C for 12 hours; after hydrothermal treatment, filtration, washing, and drying were carried out to obtain the MnO₂ sample.

[0047] MnO₂@MnO with amorphous coating on crystalline manganese dioxide x (i.e., manganese oxide support) was prepared as follows: 50 mL of KMnO₄ solution (containing 0.237 g of KMnO₄) and 50 mL of MnSO₄ solution were mixed at a molar ratio of KMnO₄:MnSO₄ of 2:1 under vigorous stirring, and then 0.5 g of the MnO₂ sample was evenly dispersed in the above solution, stirred at 30 °C for 6 h, and after filtration, washing, and drying, MnO₂@MnOx was obtained.

[0048] Ag / MnO₂@MnO x Preparation of the plasma catalyst: 0.5 g of the MnO₂@MnO x powder was dispersed in 50 mL of deionized water, and then 5 mL of 1 mmol / L silver nitrate solution was added thereto and stirred until homogeneous; 0.5 g of 30 wt% hydrogen peroxide solution was then added dropwise to the mixed solution, and after filtration, washing, and drying, and calcination at 400 °C for 3 h in a N₂ atmosphere, Ag / MnO₂@MnO x was obtained.

[0049] The SEM image and HRTEM image of the Ag / MnO₂@MnO plasma catalyst synthesized in Example 1 are shown in x (a) and Figure 1 (b) respectively, from which Ag single atoms can be seen. Figure 1 (b) respectively, from which Ag single atoms can be seen.

[0050] Performance test of the catalyst: 0.2 g of the catalyst was filled into the discharge bed area of the plasma reactor for the performance test of plasma catalytic degradation of methyl mercaptan; a pulse modulation power supply was used, and the simulated malodorous waste gas was composed of N₂, O₂, and methyl mercaptan, with the concentration of methyl mercaptan being 30 ppmv, the O₂ concentration being 20 vol%, the total gas flow rate being 2 L / min, the concentration of methyl mercaptan in the tail gas was measured by gas chromatography, and the ozone concentration in the tail gas was measured by an ozone analyzer.

[0051] According to the above performance test, the activity performance of the plasma catalyst synthesized in Example 1 in synergistic degradation of methyl mercaptan with plasma is as shown in Figure 4As shown, when the energy density is 130 J / L, the removal rate of methyl mercaptan reaches 90%; when the energy density is 150 J / L, the removal rate of methyl mercaptan reaches 100%, and the ozone in the tail gas is less than 3 ppm.

[0052] Comparative Example 1:

[0053] This comparative example is a single crystalline MnO₂, and the preparation steps are the same as those for the preparation of crystalline manganese dioxide MnO₂ in Example 1. The application conditions of this comparative example are the same as those for the performance test in Example 1.

[0054] The removal performance of the catalyst in Comparative Example 1 for methyl mercaptan is as Figure 2 . When the energy density is 130 J / L, the removal rate of methyl mercaptan reaches 67%, and at the same time, the ozone concentration in the tail gas is about 14.1 ppm. When the energy density is 150 J / L, the removal rate of methyl mercaptan reaches 91%, and the ozone in the tail gas is about 22 ppm.

[0055] Comparative Example 2:

[0056] This comparative example is a single amorphous manganese oxide, and the preparation steps are as follows: Under vigorous stirring, 50 mL of KMnO₄ solution (containing 0.237 g of KMnO₄) and 50 mL of MnSO₄ solution are mixed at a molar ratio of KMnO₄:MnSO₄ of 2:1, stirred at 30 °C for 6 h, and after filtration, washing, and drying, an amorphous manganese oxide sample is obtained. The application conditions of this comparative example are the same as those for the performance test in Example 1.

[0057] The removal performance of the catalyst in Comparative Example 2 for methyl mercaptan is as Figure 3 . When the energy density is 150 J / L, the removal rate of methyl mercaptan is only 50%, and at the same time, the ozone concentration in the tail gas is about 5 ppm. It can be seen that the response ability of this sample in the electric field is not strong, but it has good ozone utilization and decomposition ability.

[0058] Example 2:

[0059] The difference between this example and Example 1 is that the masses of the MnO₂ samples used in the preparation process of MnO₂@MnO x are 0.1 g, 0.3 g, and 0.7 g respectively, and they are named Ag / MnO₂(0.1)@MnO x , Ag / MnO₂(0.3)@MnO x and Ag / MnO₂(0.7)@MnO x , and the rest of the preparation methods and performance tests are the same as those in Example 1.

[0060] The removal performance of the catalyst in Example 2 for methyl mercaptan is as Figure 4。In a certain range, as the dosage of crystalline MnO2 increases, the removal rate of methyl mercaptan increases at the same energy density. However, too much crystalline MnO2 may instead reduce the removal effect of methyl mercaptan, and the ozone concentration in the tail gas will also increase significantly. This result indicates that the dosage of crystalline MnO2 can enhance the utilization of high-energy electrons in the field by the catalyst to a certain extent, which is beneficial to improving the discharge power. But as its dosage increases, the proportion of amorphous manganese oxide on the surface decreases, affecting the decomposition and utilization of ozone in the system. Therefore, it is necessary to balance and consider the functional performance of the catalyst in terms of discharge response and ozone decomposition.

[0061] Example 3:

[0062] The difference between this example and Example 1 lies in adjusting the concentration of silver nitrate solution used in the preparation process of Ag / MnO2@MnO x , which are 0.1 mmol / L, 0.5 mmol / L, and 1.5 mmol / L respectively, and are named Ag(0.1) / MnO2@MnO x , Ag(0.5) / MnO2@MnO x , and Ag(1.5) / MnO2@MnO x respectively. The remaining preparation methods and performance tests are the same as those in Example 1.

[0063] The removal performance of the catalyst in Example 3 for methyl mercaptan is as Figure 5 . Considering the results of Example 1, as the concentration of silver nitrate increases from 0.1 mmol / L to 1.5 mmol / L, the removal rate of methyl mercaptan shows a trend of first increasing and then decreasing. At an energy density of 130 J / L, the removal rate of Ag / MnO2@MnO x for methyl mercaptan can reach 90%, which is significantly better than that of Ag(0.1) / MnO2@MnO x and Ag(0.5) / MnO2@MnO x . This may be because the introduction of Ag single atoms can effectively enhance the adsorption of methyl mercaptan molecules on the catalyst. When the concentration of added silver nitrate continues to increase to 1.5 mmol / L, the removal rate of Ag(1.5) / MnO2@MnO x for methyl mercaptan slightly decreases to 86%. This is mainly because as the concentration of added silver ions increases, they agglomerate on the surface of manganese oxide and cannot continue to exist in the form of single atoms, thereby affecting the performance.

[0064] Example 4:

[0065] In this example, no catalyst is filled, and the degradation experiment of methyl mercaptan is carried out using only plasma.

[0066] Performance test: A pulse-modulated power supply was used. The simulated malodorous waste gas was composed of N2, O2 and methyl mercaptan, with the concentration of methyl mercaptan being 30 ppmv, the O2 concentration being 20 vol%, and the total gas flow rate being 2 L / min. The concentration of methyl mercaptan in the tail gas was determined by gas chromatography, and the ozone concentration in the tail gas was determined by an ozone meter.

[0067] The removal performance of methyl mercaptan by the single plasma in Example 4 is as Figure 6 follows. Under the condition of the single plasma, the removal rate of methyl mercaptan was only 42% at 150 J / L, and the ozone concentration in the tail gas was as high as 40 ppm. After adding the Ag / MnO2@MnO x catalyst of Example 1, at the same energy input, the removal rate of methyl mercaptan could reach 100%, and at the same time, the ozone in the tail gas was only 2.5 ppm.

[0068] In summary, the plasma catalyst provided by the present invention shows significantly better performance in the plasma catalytic degradation of sulfur-containing malodorous pollutants than the single plasma technology. At the same time, it can effectively control the ozone escape amount in the tail gas, reduce secondary pollution, and provide an efficient catalyst with industrialization potential for the plasma catalytic degradation of malodorous pollutants at the present stage.

[0069] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A plasma catalyst, characterized in that, It includes a manganese oxide support and Ag single atoms supported on the manganese oxide support; The manganese oxide support includes rod-shaped crystalline manganese dioxide and amorphous manganese oxide wrapped around the outer layer of the crystalline manganese dioxide.

2. The plasma catalyst according to claim 1, characterized in that, The mass ratio of the Ag single atoms to the manganese oxide support is 1:500 to 1200, preferably 1:700 to 1200.

3. The plasma catalyst according to claim 1, wherein The mass ratio of the amorphous manganese oxide to the crystalline manganese dioxide is 1:2 to 20, preferably 1:2 to 3.

4. The preparation method of the plasma catalyst according to any one of claims 1 to 3, characterized in that It includes the steps: 1) Uniformly disperse rod-shaped crystalline manganese dioxide in the mixed solution B of potassium permanganate and manganese sulfate, stir and react, then perform solid-liquid separation, take the solid, wash and dry it to obtain the manganese oxide support; 2) Disperse the manganese oxide support in deionized water, then add a silver nitrate solution thereto, mix well, dropwise add a hydrogen peroxide solution, stir and react, then perform solid-liquid separation, take the solid, wash and dry it, and calcine it in a non-oxidizing atmosphere to obtain the plasma catalyst.

5. The preparation method according to claim 4, characterized in that, The preparation method of the rod-shaped crystalline manganese dioxide includes: Prepare the mixed solution A of potassium permanganate and manganese sulfate, and perform a hydrothermal reaction at 100 to 160 °C, preferably 110 to 150 °C, and further preferably 130 to 140 °C to obtain the rod-shaped crystalline manganese dioxide.

6. The preparation method according to claim 5, characterized in that, In the mixed solution A, the molar ratio of potassium permanganate to manganese sulfate is 1 to 5:1; In the preparation method of the rod-shaped crystalline manganese dioxide, the time of the hydrothermal reaction is 6 to 24 hours.

7. The preparation method according to claim 4, wherein In the mixed solution B, the molar ratio of potassium permanganate to manganese sulfate is 1 to 5:1; In step 1), the mass ratio of the crystalline manganese dioxide to potassium permanganate in the mixed solution B is (0.1 to 1):(0.2 to 0.3), preferably (0.3 to 0.8):(0.2 to 0.3), and further preferably (0.4 to 0.6):(0.2 to 0.3); In step 1), the temperature of the stirring reaction is 15 to 40 °C, and the time is 4 to 8 hours.

8. The preparation method according to claim 4, characterized in that, In step 2): The molar amount of silver nitrate in the added silver nitrate solution to the mass of the manganese oxide support is (1 - 20)×10 - 3 mmol:1 g, preferably (5 - 15)×10 -3 mmol:1 g, more preferably (8 - 12)×10 -3 mmol:1 g; The ratio of the mass of H2O2 in the added hydrogen peroxide solution to the molar amount of silver nitrate in the added silver nitrate solution is 0.01 - 0.05 g:(1×10 -3 ) mmol; The non-oxidizing atmosphere is a nitrogen atmosphere and / or a noble gas atmosphere; The temperature of the calcination is 300 to 500 °C, and the time is 3 to 4 hours.

9. Use of the plasma catalyst according to any one of claims 1 to 3 in the plasma catalytic degradation of methyl mercaptan, characterized in that, The plasma catalyst is located in the discharge area where the plasma reactor generates plasma or after the discharge area. A mixed gas containing methyl mercaptan and an oxidizing gas passes through the discharge area or sequentially passes through the discharge area and the plasma catalyst. Under the combined action of the plasma and the plasma catalyst, methyl mercaptan is degraded.

10. The application according to claim 9, wherein The oxidizing gas includes at least one of oxygen and ozone; The plasma catalyst can degrade methyl mercaptan by using ozone.

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