An anti-poisoning high-entropy oxide catalyst applied to multi-pollutant removal of coal-fired flue gas, a preparation method and application thereof

Abstract

The application provides a high-entropy oxide catalyst and a preparation method and application thereof, and relates to the technical field of catalysts.The high-entropy oxide catalyst provided by the application comprises at least five kinds of metal elements, including Mn, Ce, Fe, Cu, Co and Cr.The application utilizes the synergistic effect among the elements of the high-entropy oxide, selects several elements which are good for the catalytic oxidation effect of the coal-fired flue gas, integrates the elements in the same lattice of the high-entropy oxide, and makes the catalyst have the volatile organic pollutant removal capacity and the resistance to the complex interference gas of the coal-fired flue gas.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a high-entropy oxide catalyst and a preparation method and application thereof. BACKGROUND

[0002] Volatile organic compounds (VOCs) are important precursors of various secondary pollutants, and their emissions greatly accelerate the formation of secondary aerosols, fine particulate matter (PM2.5) and ozone (O3), etc., and are the culprits of environmental problems such as acid rain, photochemical smog, ozone depletion and greenhouse effect, and cause direct harm to the human body. The Ecological Environment Statistical Yearbook released by the Ministry of Ecological Environment of China in 2020 pointed out that the emission of VOCs from coal-fired flue gas has reached 6.1 million tons, and has a trend of increasing year by year, and coal-fired emission has become one of the important sources of VOCs in the atmosphere. At present, the main methods for treating VOCs include physical adsorption, catalytic oxidation, oxidation absorption, etc. The catalytic oxidation technology has the advantages of high efficiency and low cost in the treatment of VOCs, and is considered as one of the most effective methods for removing VOCs pollutants.

[0003] In the coal-fired flue gas, there are many factors affecting catalytic oxidation, and the main factor is that the composition of the actual industrial coal-fired flue gas is too complex, and in the actual industrial flue gas, water vapor and sulfur dioxide will interfere with the removal efficiency of catalytic oxidation. SUMMARY

[0004] The purpose of the present application is to provide a high-entropy oxide catalyst and a preparation method and application thereof. The high-entropy oxide catalyst provided by the present application has good catalytic oxidation efficiency for volatile organic pollutants in the presence of water vapor and sulfur dioxide.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0006] The present application provides a high-entropy oxide catalyst, wherein the metal elements include at least five of Mn, Ce, Fe, Cu, Co and Cr.

[0007] Preferably, the metal elements include Mn and Ce.

[0008] Preferably, the specific surface area of the high-entropy oxide is 1.5-6 m2 / g.

[0009] The present application provides a preparation method of the high-entropy oxide catalyst described in the above-mentioned solution, comprising the following steps:

[0010] The precursors corresponding to the metal elements and the combustion-supporting agent are dissolved in water to obtain a dissolution solution; the water in the dissolution solution is removed to obtain a high-entropy oxide precursor; the metal elements include at least five of Mn, Ce, Fe, Cu, Co and Cr.

[0011] The high-entropy oxide precursor is calcined and quenched to obtain the high-entropy oxide catalyst.

[0012] Preferably, the combustion-supporting agent comprises one or more of glycine, urea and citric acid.

[0013] Preferably, the calcination temperature is 1000-1200℃, and the time is 20-40min; and the quenching is water quenching.

[0014] Preferably, after the quenching, the obtained high-entropy oxide is mixed with a surfactant solution and subjected to ball milling; the mass of the surfactant in the surfactant solution is 0-50% of the mass of the high-entropy oxide.

[0015] Preferably, the ball milling time is more than 6h.

[0016] The application provides the high-entropy oxide catalyst described in the above scheme or the application of the high-entropy oxide catalyst described in the above scheme in catalyzing the oxidation of volatile organic pollutants in coal-fired flue gas.

[0017] Preferably, the coal-fired flue gas contains other pollutants, and the other pollutants include one or more of mercury vapor, nitrogen oxide, water vapor and sulfur oxide.

[0018] The application provides a high-entropy oxide catalyst, which comprises at least five of Mn, Ce, Fe, Cu, Co and Cr. The application utilizes the synergistic effect of high-entropy oxides, selects several elements that are good for the catalytic oxidation of coal-fired flue gas, integrates the elements in the same lattice of the high-entropy oxide, and makes the catalyst have resistance to complex interference gas and the ability to remove volatile organic pollutants. Meanwhile, the application can complete the combined removal of nitrogen oxide and mercury vapor without affecting the removal of volatile organic pollutants.

[0019] The application provides a preparation method of the high-entropy oxide catalyst described in the above scheme. The application utilizes soft-template surfactant-assisted ball milling, and increases the specific surface area of the high-entropy oxide and mechanically activates the surface of the high-entropy oxide by means of ball milling. The increase of the specific surface area can effectively expose the covered active sites, and the mechanical activation of the surface can effectively increase the migration ability of lattice oxygen and promote the generation of oxygen vacancies, thereby improving the catalytic oxidation efficiency of volatile organic pollutants. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The XRD characterization images of Example 1 and Comparative Example 1;

[0021] Figure 2 The catalytic effect comparison chart of the catalysts prepared in Example 1 and Comparative Example 1 in the flue gas environment without other pollutants.

[0022] Figure 3 Catalytic effect diagram of the catalyst prepared for Example 1 in a complex flue gas environment;

[0023] Figure 4 Catalytic effect diagram of the catalyst prepared for Comparative Example 1 in a complex flue gas environment;

[0024] Figure 5 Influence diagram of the amount of surfactant on the catalytic effect of the catalyst during ball milling;

[0025] Figure 6 Catalytic efficiency diagram of the catalyst treated by ball milling with different amounts of surfactant at 300 DEG C on VOC;

[0026] Figure 7 Influence diagram of the ball milling time on the catalytic effect of the catalyst;

[0027] Figure 8 Catalytic effect comparison diagram of the catalysts prepared in Example 8 and Comparative Example 2;

[0028] Figure 9 Catalytic effect diagram of the catalyst prepared in Example 8 on various pollutants under different pollutant conditions. DETAILED DESCRIPTION

[0029] The present application provides a high-entropy oxide catalyst, and the metal elements include at least five of Mn, Ce, Fe, Cu, Co and Cr. The present application does not have special requirements for the ratio of each metal element, and meets the definition of high-entropy oxide. In the embodiments of the present application, each metal element is preferably in equimolar ratio.

[0030] In the present application, the metal elements preferably include Mn and Ce. In the present application, when Mn and Ce are contained in the high-entropy oxide catalyst, the catalyst exhibits more excellent catalytic efficiency on flue gas.

[0031] In the present application, the specific surface area of the high-entropy oxide is preferably 1.5-6 m 2 / g. In the present application, the larger the specific surface area of the high-entropy oxide, the more active sites are exposed, and the removal effect of volatile organic pollutants in flue gas is better.

[0032] The present application integrates a plurality of transition group elements with the ability to treat flue gas into the same lattice to form a single spinel phase high-entropy oxide for catalytic oxidation of volatile organic compounds, which has good catalytic oxidation efficiency, and makes the catalyst have complex interference gas resistance and combined removal ability.

[0033] The application provides a preparation method of the high-entropy oxide catalyst.

[0034] The precursors corresponding to the metal elements and a combustion-supporting agent are dissolved in water to obtain a solution; water in the solution is removed to obtain a high-entropy oxide precursor; the metal elements include at least five of Mn, Ce, Fe, Cu, Co and Cr;

[0035] The high-entropy oxide precursor is calcined and quenched to obtain the high-entropy oxide catalyst.

[0036] In the application, the raw materials used are all commercially available goods well known in the art, unless otherwise specified.

[0037] In the application, the precursors corresponding to the metal elements are preferably nitrate salts of the metal elements; the application preferably uses metal nitrates as combustion precursors, because nitrates have pure pyrolysis products at high temperatures, and nitrates generally have higher solubility than sulfates and hydrochlorides. In the application, the combustion-supporting agent preferably includes one or more of glycine, urea and citric acid, and is more preferably glycine. The application uses glycine as a combustion-supporting agent, which has the advantage of relatively pure combustion products. The application does not have special requirements for the amount of the combustion-supporting agent, which can be excessive relative to the metal elements. In the embodiments of the application, the molar ratio of the combustion-supporting agent to all the metal elements is preferably 3:1. The application does not have special requirements for the amount of water, which can completely dissolve the precursors corresponding to the metal elements and the combustion-supporting agent. In the application, the water is preferably deionized water. The application preferably dissolves under stirring. The application achieves uniform mixing at the ionic level by dissolving the precursors corresponding to the metal elements and the combustion-supporting agent in water, thereby ensuring that a single-phase material is sintered.

[0038] After obtaining the solution, the application removes water in the solution to obtain a high-entropy oxide precursor. In the application, the preferred way to remove water in the solution is heating; the heating is preferably performed in an oven, and the temperature of the heating is preferably 60-100℃, and more preferably 75℃. The application does not have special requirements for the time of the heating, which can be removed without affecting calcination.

[0039] After obtaining the high-entropy oxide precursor, the application calcines and quenches the high-entropy oxide precursor to obtain the high-entropy oxide catalyst.

[0040] In the present application, the temperature of the calcination is preferably 1000-1200 DEG C, more preferably 1050-1150 DEG C, and further preferably 1100 DEG C; the time of the calcination is preferably 20-40 min, more preferably 25-35 min. In the present application, the calcination is preferably performed in an air atmosphere. In the present application, the quenching is preferably water quenching. The present application utilizes rapid quenching to obtain high-entropy oxides in spinel form.

[0041] In order to increase the specific surface area of the high-entropy oxides, after the quenching, the present application preferably mixes the obtained high-entropy oxides with a surfactant solution and performs ball milling.

[0042] In the present application, the surfactant preferably includes oleylamine and oleic acid, and the mass ratio of the oleylamine and the oleic acid is preferably 1:1; the mass of the surfactant is preferably 0-50% of the mass of the high-entropy oxides, more preferably 5-30%, and further preferably 10-15%. In the present application, the surfactant solution is preferably obtained by dissolving the surfactant in n-heptane, and the present application does not have special requirements for the amount of the n-heptane, which should be reduced as much as possible under the premise of ensuring the dissolution of the surfactant. In the present application, the ball-to-material ratio of the ball milling is preferably 10:1; the time of the ball milling is preferably more than 6 h, more preferably more than 12 h, and further preferably 12-18 h. In the present application, as the ball milling time increases, the catalytic effect of the high-entropy oxides gradually improves.

[0043] In the present application, after the ball milling is completed, the present application preferably adds a volatile organic solvent to the ball-milled material for washing. In the present application, the washing preferably includes: adding a volatile organic solvent to the ball-milled material, standing for 30 min until the solution is layered, pouring off the excess supernatant, repeating the step until the supernatant poured off is clear, does not appear yellowish, and does not show acidity in pH value, and thus the washing is completed.

[0044] In the present application, the volatile organic solvent preferably includes ethanol; the present application utilizes washing to remove the surfactant, and can ensure that the residual amount of the volatile organic solvent is extremely low.

[0045] The present application utilizes soft-template surfactant-assisted ball milling, and utilizes the ball milling means to increase the specific surface area of the high-entropy oxides and mechanically activate the surface of the high-entropy oxides. The increase of the specific surface area can effectively expose the covered active sites, and the mechanical activation of the surface can effectively increase the migration ability of the lattice oxygen and promote the generation of oxygen vacancies, and thus improve the catalytic oxidation efficiency of the volatile organic pollutants in the flue gas.

[0046] The present application provides the high-entropy oxide catalyst described in the above scheme or the application of the high-entropy oxide catalyst described in the above scheme in catalyzing the oxidation of volatile organic pollutants in the flue gas of coal-fired power plants.

[0047] The present application does not have special requirements for the source of the coal-fired flue gas, and the coal-fired flue gas from a source well known in the art can be used, specifically the coal-fired flue gas from a thermal power plant. In the present application, the coal-fired flue gas preferably contains residual pollutants, and the residual pollutants preferably include one or more of mercury vapor, nitrogen oxide, water vapor, and sulfur oxide; the content of the volatile organic pollutants in the coal-fired flue gas is preferably 20-80 ppm, and more preferably 50 ppm.

[0048] The present application does not have special requirements for the specific type of volatile organic pollutants, and any volatile organic pollutants well known in the art can be used. In the examples of the present application, o-xylene is specifically used to simulate volatile organic pollutants.

[0049] The present application does not have special requirements for the conditions of catalytic oxidation, and the catalytic oxidation conditions well known in the art can be used. In the examples and comparative examples of the present application, the reaction temperature of the catalytic oxidation is 200-450°C, and the space velocity is constant at 30000h -1 .

[0050] The high-entropy oxide catalyst and the preparation method thereof provided by the present application will be described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0051] Comparative Example 1 (five-element chemical precipitation)

[0052] An equal amount of 8 mmol of manganese nitrate, cerium nitrate, iron nitrate, cobalt nitrate, and chromium nitrate was dissolved in 400 mL of deionized water to obtain a solution with a total cation concentration of 0.1 M (a concentration of 0.02 M for each cation), which was labeled as solution A; 60 mmol of K2CO3 was dissolved in 400 mL of deionized water to form a solution with an ionic concentration of 0.15 M, which was labeled as solution B.

[0053] The co-precipitation was performed in a reverse precipitation manner, i.e., solution A was slowly added to solution B. During vigorous stirring, 400 mL of solution A was added to 400 mL of solution B at a speed of about 20 mL / min. Continuous stirring was performed for 30 min, and finally the gel-like co-precipitate was filtered and washed repeatedly with deionized water, and dried overnight in an environment at 60°C. The sample was labeled as CrMnFeCoCeO x .

[0054] The catalyst sample was placed in a reactor, and the reaction temperature was 200-450°C, and the space velocity was 30000h -1The conditions, 40 ppm o-xylene, 5 vol.% O2and carrier gas N2were passed. The catalytic efficiency for o-xylene was 26.32% to 65.16%; under the flue gas conditions of additionally passing 5 vol.% H2O, the catalytic efficiency for o-xylene was 22.42% to 52.96%; under the flue gas conditions of additionally passing 200 ppm SO2, the catalytic efficiency for o-xylene was 16.52% to 36.15%; under the flue gas conditions of additionally passing 5 vol.% H2O and 200 ppm SO2, the catalytic efficiency for o-xylene was 10.28% to 18.87%. The specific results are shown in Table 1.

[0055] Note: The catalytic efficiency refers to the catalytic efficiency for VOC, which is calculated according to Formula 1:

[0056]

[0057] Wherein, η represents the catalytic oxidation efficiency, C (in) is the concentration (ppm) of pollutants entering the reactor, C (out) is the concentration (ppm) of pollutants at the outlet of the reactor.

[0058] Table 1 Catalytic oxidation efficiency (%) of Comparative Example 1 under different conditions

[0059] CrMnFeCoCeO x ]]> 200℃ 250℃ 300℃ 350℃ 400℃ 450℃ VOC 26.32 33.03 42.47 54.43 60.73 65.16 [CAT+H2O] 22.42 30.71 36.26 41.16 50.80 52.96 [ VOC + SO2 ] 16.52 21.96 22.47 24.36 30.98 36.15 [ VOC + H2O + SO2 ] 10.28 12.81 11.35 13.17 14.66 18.87

[0060] Example 1 (five-element high-entropy)

[0061] An equal amount of 10 mmol of manganese nitrate, cerium nitrate, iron nitrate, cobalt nitrate and chromium nitrate was dissolved in 100 mL of deionized water, 12 g of glycine was added as a combustion improver, and the mixture was magnetically stirred at room temperature for 30 min to obtain a uniform red-brown gel. Subsequently, the sol was heated in an oven at 70°C for 12 h to remove excess deionized water. The obtained red-brown gel was placed in a quartz boat and put into a preheated to 1200°C tube furnace, and calcined under air atmosphere for 30 min. The obtained sample was directly taken out, quickly added to water to quench to room temperature and ground into powder, and a high-entropy oxide powder was obtained. The sample was marked as (CrMnFeCoCe)3O4.

[0062] The catalyst sample was placed in the reactor, and the reaction temperature was 200-450°C, the space velocity was 30000 h -1The conditions, 40 ppm o-xylene, 5 vol.% O2 and carrier gas N2 were passed. The catalytic efficiency for o-xylene was 45.12% to 92.54%; under the flue gas condition of additionally passing 5 vol.% H2O, the catalytic efficiency for o-xylene was 31.69% to 83.42%; under the flue gas condition of additionally passing 200 ppm SO2, the catalytic efficiency for o-xylene was 25.10% to 86.69%; under the flue gas condition of additionally passing 5 vol.% H2O and 200 ppm SO2, the catalytic efficiency for o-xylene was 35.66% to 87.08%. The specific catalytic results are shown in Table 2.

[0063] Table 2 Catalytic oxidation efficiency (%) of Example 1 under different conditions

[0064]

[0065] The samples of Example 1 and Comparative Example 1 were subjected to XRD characterization, and the results are shown in Figure 1 . It can be seen from Figure 1 that there is a difference in crystal morphology between Example 1 and Comparative Example 1, which can indicate that the chemical precipitation method cannot form a single crystal phase of high-entropy oxide.

[0066] The results of Example 1 and Comparative Example 1 were plotted into a graph, and the results are shown in Figures 2-4 . It can be seen from Figure 2 that the catalytic efficiency of high-entropy oxides formed by Mn, Ce, Fe, Cu, Co and Cr has a significant advantage over that of multi-phase oxides; it can be seen from Figure 3 and Figure 4 that high-entropy oxides formed by Mn, Ce, Fe, Co and Cr have the ability to catalyze o-xylene in a complex flue gas environment.

[0067] In the following Examples 2-10, the untreated high-entropy oxide powder used was the oxide powder prepared in Example 1; in the following Comparative Example 2, the untreated multi-phase oxide powder used was the oxide powder prepared in Comparative Example 1.

[0068] Example 2 (high-entropy ball milling 0%)

[0069] To improve the specific surface area of high-entropy oxides, the high-entropy oxide powder was subjected to ball milling. During ball milling, the ball-to-material ratio was 10:1, that is, 1 g of high-entropy oxide powder was added to each ball mill tank, and 10 g of grinding balls (3 large balls with a diameter of 12 mm, 5 medium balls with a diameter of 8 mm, and 10 small balls with a diameter of 6 mm) were added. After ball milling for 12 h, the sample was directly taken out.

[0070] The catalyst sample was placed in a reactor, and the reaction temperature was 200-450℃, the space velocity was 30000 h-1, and the flue gas conditions were as follows: 40 ppm o-xylene, 5 vol.% O2 and carrier gas N2 were passed. The catalytic efficiency for o-xylene was 45.12% to 92.54%; under the flue gas condition of additionally passing 5 vol.% H2O, the catalytic efficiency for o-xylene was 31.69% to 83.42%; under the flue gas condition of additionally passing 200 ppm SO2, the catalytic efficiency for o-xylene was 25.10% to 86.69%; under the flue gas condition of additionally passing 5 vol.% H2O and 200 ppm SO2, the catalytic efficiency for o-xylene was 35.66% to 87.08%. The specific catalytic results are shown in Table 2. -1Under the conditions, 40 ppm o-xylene, 5 vol.% O2 and carrier gas N2 were passed. The catalytic efficiency for o-xylene was 64.22% to 100%.

[0071] Example 3 (high-entropy ball milling 10%)

[0072] To improve the specific surface area of the high-entropy oxide, a surfactant with a mass ratio of 10% of the sample powder was subsequently added. The surfactant was used in the form of a solution, the solvent was n-heptane, and the surfactant was a mixture of oleic acid and oleylamine in a certain mass ratio. During ball milling, the ball-to-material ratio was 10:1, that is, 1 g of high-entropy oxide powder was added to each ball mill tank, 10 g of grinding balls (3 large balls with a diameter of 12 mm, 5 medium balls with a diameter of 8 mm, and 10 small balls with a diameter of 6 mm) were added, and 2 mL of n-heptane was added to completely dissolve 0.58 mL of oleic acid and 0.61 mL of oleylamine surfactant. After ball milling for 12 h, a large amount of ethanol was added to the ball mill tank for washing, and the washed black suspension was transferred to a beaker. After standing for 30 min, the solution was layered, and the supernatant was poured out. This process was repeated 5-7 times until the supernatant was clear, not yellowish, and not acidic. At this point, the washing was completed, and the sample was directly taken out.

[0073] The catalyst sample was placed in the reactor, and the reaction temperature was 200-450°C, the space velocity was 30000 h-1, and the reaction time was 1 h. -1 Under the conditions, 40 ppm o-xylene, 5 vol.% O2 and carrier gas N2 were passed. The catalytic efficiency for o-xylene was 64.22% to 100%.

[0074] Example 4 (high-entropy ball milling 15%)

[0075] To improve the specific surface area of the high-entropy oxide, a surfactant with a mass ratio of 15% of the sample powder was subsequently added. The solvent was n-heptane, and the solute was a mixture of oleic acid and oleylamine in a certain ratio. During ball milling, the ball-to-material ratio was 10:1, that is, 1 g of high-entropy oxide powder was added to each ball mill tank, 10 g of grinding balls (3 large balls with a diameter of 12 mm, 5 medium balls with a diameter of 8 mm, and 10 small balls with a diameter of 6 mm) were added, and 2 mL of n-heptane was added to completely dissolve 0.87 mL of oleic acid and 0.91 mL of oleylamine surfactant. After ball milling for 12 h, a large amount of ethanol was added to the ball mill tank for washing, and the washed black suspension was transferred to a beaker. After standing for 30 min, the solution was layered, and the supernatant was poured out. This process was repeated 5-7 times until the supernatant was clear, not yellowish, and not acidic. At this point, the washing was completed, and the sample was directly taken out.

[0076] The catalyst sample was placed in the reactor, and the reaction temperature was 200-450°C, the space velocity was 30000 h-1, and the reaction time was 1 h. -1Under the conditions, 40 ppm o-xylene, 5 vol.% O2 and carrier gas N2 were passed. The catalytic efficiency for o-xylene was 73.44% to 100%.

[0077] Example 5 (high-entropy ball milling 20%)

[0078] To improve the specific surface area of the high-entropy oxide, a surfactant was subsequently added, which accounted for 20% of the mass of the sample powder, the solvent was n-heptane, and the solute was a mixture of oleic acid and oleylamine in a certain proportion. During ball milling, the ball-to-material ratio was 10:1, that is, 1 g of high-entropy oxide powder was added to each ball mill tank, 10 g of grinding balls (3 large balls with a diameter of 12 mm, 5 medium balls with a diameter of 8 mm, and 10 small balls with a diameter of 6 mm), and 2 mL of n-heptane was added to completely dissolve 1.16 mL of the surfactant of oleic acid and 1.22 mL of oleylamine. After ball milling for 12 h, a large amount of ethanol was added to the ball mill tank for washing, and the washed black suspension was transferred to a beaker. After standing for 30 min, the solution was layered, and the supernatant was poured out. This process was repeated 5-7 times until the supernatant was clear, not yellowish, and not acidic. At this point, the washing was completed, and the sample was directly taken out.

[0079] The catalyst sample was placed in the reactor, the reaction temperature was 200-450℃, the space velocity was 30000h-1, and the reaction time was 1-4 h. -1 Under the conditions, 40 ppm o-xylene, 5 vol.% O2 and carrier gas N2 were passed. The catalytic efficiency for o-xylene was 68.59% to 100%.

[0080] Example 6 (high-entropy ball milling 30%)

[0081] To improve the specific surface area of the high-entropy oxide, a surfactant was subsequently added, which accounted for 30% of the mass of the sample powder, the solvent was n-heptane, and the solute was a mixture of oleic acid and oleylamine in a certain proportion. During ball milling, the ball-to-material ratio was 10:1, that is, 1 g of high-entropy oxide powder was added to each ball mill tank, 10 g of grinding balls (3 large balls with a diameter of 12 mm, 5 medium balls with a diameter of 8 mm, and 10 small balls with a diameter of 6 mm), and 2 mL of n-heptane was added to completely dissolve 1.74 mL of the surfactant of oleic acid and 1.83 mL of oleylamine. After ball milling for 12 h, a large amount of ethanol was added to the ball mill tank for washing, and the washed black suspension was transferred to a beaker. After standing for 30 min, the solution was layered, and the supernatant was poured out. This process was repeated 5-7 times until the supernatant was clear, not yellowish, and not acidic. At this point, the washing was completed, and the sample was directly taken out.

[0082] The catalyst sample was placed in the reactor, the reaction temperature was 200-450℃, the space velocity was 30000h-1, and the reaction time was 1-4 h. -1The conditions are that 40 ppm o-xylene, 5 vol.% O2 and carrier gas N2 are passed through. The catalytic efficiency for o-xylene is 68.93% to 100%.

[0083] The catalytic results of examples 1-6 are shown in Table 3.

[0084] Table 3 VOC catalytic oxidation efficiency (%) of examples 1-6 at different temperatures

[0085] (CrMnFeCoCe) 3 O 4 ]]> 200℃ 250℃ 300℃ 350℃ 400℃ 450℃ 0％ 60.53 69.14 78.62 91.82 100 100 10％ 64.22 75.43 84.72 96.17 100 100 15％ 73.44 85.72 97.33 99.62 100 100 20％ 68.59 71.37 83.68 97.81 100 100 30％ 68.93 72.69 83.26 98.02 100 100 Untreated 45.12 49.20 64.84 81.28 88.26 92.54

[0086] The results of examples 1-6 are plotted in a graph, as shown in Figures 5-6 It can be seen from Figure 5 that the high-entropy oxides formed by Mn, Ce, Fe, Co and Cr have a significant increase in catalytic efficiency after ball milling, and the degree of increase in catalytic efficiency is related to the amount of surfactant; from Figure 5 and Figure 6 it can be seen that the catalytic ability of the high-entropy oxide for o-xylene is the largest after being treated by 15% surfactant assisted ball milling.

[0087] Example 7 (high-entropy ball milling for 6h)

[0088] To improve the specific surface area of the high-entropy oxide, 15% of the sample powder by mass is added, and the solvent is n-heptane, and the solute is oleic acid, oleylamine, etc. mixed in a certain proportion to form a surfactant. When ball milling, the ball-to-material ratio is 10:1, that is, 1 g of high-entropy oxide powder is added to each ball milling tank, 10 g of grinding balls (3 large balls with a diameter of 12 mm, 5 medium balls with a diameter of 8 mm, and 10 small balls with a diameter of 6 mm), and 2 mL of n-heptane is added to completely dissolve 0.87 mL of oleic acid and 0.91 mL of oleylamine surfactant. After ball milling for 6h, a large amount of ethanol is added to the ball milling tank for washing, and the washed black suspension is transferred to a beaker. After standing for 30 min, the solution is layered, and the supernatant is poured out. Repeat this process 5-7 times until the supernatant is clear, not yellowish, and not acidic. At this point, the washing is complete, and the sample can be taken out directly.

[0089] The catalyst sample is placed in a reactor under the conditions of a reaction temperature of 200-450℃ and an airspeed of 30000h -1 The conditions are that 40 ppm o-xylene, 5 vol.% O2 and carrier gas N2 are passed through. The catalytic efficiency for o-xylene is 68.93% to 100%.

[0090] Example 8 (high-entropy ball milling for 18h)

[0091] To increase the specific surface area of ​​the high-entropy oxide, a surfactant, comprising 15% by mass of the sample powder, was subsequently added. This surfactant consisted of n-heptane as the solvent and a mixture of oleic acid and oleylamine as the solutes. During ball milling, the ball-to-powder ratio was 10:1, meaning 1g of high-entropy oxide powder and 10g of grinding balls (3 large balls with a diameter of 12mm, 5 medium balls with a diameter of 8mm, and 10 small balls with a diameter of 6mm) were added to each milling jar. 2mL of n-heptane was added to completely dissolve 0.87mL of oleic acid and 0.91mL of oleylamine surfactant. After milling for 18 hours, a large amount of ethanol was added to the milling jar for rinsing, and the resulting black suspension was transferred to a beaker. The solution was allowed to stand for 30 minutes until it separated into layers, and the supernatant was poured off. This process was repeated 5–7 times until the supernatant was clear, not pale yellow, and not acidic at pH. The washing process was then complete, and the sample could be directly removed.

[0092] The catalyst sample was placed in the reactor and reacted at a temperature of 200–450 °C and a space velocity of 30,000 h⁻¹. -1 Under the conditions of introducing 40 ppm of o-xylene, 5 vol.% O2, and carrier gas N2, the catalytic efficiency for o-xylene ranged from 75.53% to 100%; with the additional introduction of 5 vol.% H2O into the flue gas, the catalytic efficiency for o-xylene ranged from 77.69% to 100%.

[0093] Example 9 (High-entropy ball milling for 24 hours)

[0094] To increase the specific surface area of ​​the high-entropy oxide, a surfactant, comprising 15% by mass of the sample powder, was subsequently added. This surfactant consisted of n-heptane as the solvent and oleic acid and oleylamine as the solutes in equal proportions. During ball milling, the ball-to-powder ratio was 10:1, meaning 1g of high-entropy oxide powder, 10g of grinding balls (3 large balls with a diameter of 12mm, 5 medium balls with a diameter of 8mm, and 10 small balls with a diameter of 6mm) were added to each milling jar. 2mL of n-heptane was added to completely dissolve 0.87mL of oleic acid and 0.91mL of oleylamine surfactant. After milling for 24 hours, a large amount of ethanol was added to the milling jar for rinsing, and the resulting black suspension was transferred to a beaker. The solution was allowed to stand for 30 minutes until it separated into layers, and the supernatant was poured off. This process was repeated 5–7 times until the poured-off supernatant was clear, not pale yellow, and had a non-acidic pH. The washing process was then complete, and the sample could be directly removed.

[0095] The catalyst sample was placed in the reactor and reacted at a temperature of 200–450 °C and a space velocity of 30,000 h⁻¹. -1 Under these conditions, 40 ppm of o-xylene, 5 vol.% O2, and carrier gas N2 were introduced. The catalytic efficiency for o-xylene ranged from 76.52% to 100%.

[0096] Example 10 (High-entropy ball milling for 30 hours)

[0097] To improve the specific surface area of high-entropy oxides, 15% of the sample powder by mass was added, the solvent was n-heptane, and the solute was a surfactant mixed in a certain proportion from oleic acid and oleylamine. During ball milling, the ball-to-material ratio was 10:1, that is, 1 g of high-entropy oxide powder was added to each ball mill tank, 10 g of grinding balls (3 large balls with a diameter of 12 mm, 5 medium balls with a diameter of 8 mm, and 10 small balls with a diameter of 6 mm), and 2 mL of n-heptane was added to completely dissolve 0.87 mL of oleic acid and 0.91 mL of oleylamine surfactant. After ball milling for 30 h, a large amount of ethanol was added to the ball mill tank for flushing, and the washed black suspension was transferred to a beaker. After standing for 30 min, the solution was layered, and the supernatant was poured out. This process was repeated 5-7 times until the supernatant was clear, not yellowish, and not acidic. At this point, the washing was complete, and the sample was directly removed.

[0098] The catalyst sample was placed in a reactor under the conditions of a reaction temperature of 200-450°C, an airspeed of 30000 h -1 , and the introduction of 40 ppm of o-xylene, 5 vol.% of O2, and N2 as a carrier gas. The catalytic efficiency for o-xylene was 72.67% to 100%.

[0099] The catalytic results of Examples 4, 7-10 are shown in Table 4.

[0100] Table 4: VOC catalytic oxidation efficiency (%) of Example 4 and Examples 7-10 at different temperatures

[0101]

[0102] The results of Examples 4, 7-10 were plotted, and the results are shown in Figure 7 , which shows that the time of ball milling treatment of high-entropy oxides has an effect on their catalytic efficiency. The ability to catalyze o-xylene is maximized when the ball milling treatment time is 18 h with the assistance of 15% surfactant.

[0103] Comparative Example 2 (non-high-entropy ball milling 15%, 18 h)

[0104] To improve the specific surface area of high-entropy oxides, 15% of the sample powder by mass was added, the solvent was n-heptane, and the solute was a surfactant mixed in a certain proportion from oleic acid and oleylamine. During ball milling, the ball-to-material ratio was 10:1, that is, 1 g of high-entropy oxide powder was added to each ball mill tank, 10 g of grinding balls (3 large balls with a diameter of 12 mm, 5 medium balls with a diameter of 8 mm, and 10 small balls with a diameter of 6 mm), and 2 mL of n-heptane was added to completely dissolve 0.87 mL of oleic acid and 0.91 mL of oleylamine surfactant. After ball milling for 30 h, a large amount of ethanol was added to the ball mill tank for flushing, and the washed black suspension was transferred to a beaker. After standing for 30 min, the solution was layered, and the supernatant was poured out. This process was repeated 5-7 times until the supernatant was clear, not yellowish, and not acidic. At this point, the washing was complete, and the sample was directly removed. xThe specific surface area of the sample powder is 15%, the solvent is n-heptane, and the solute is a surfactant mixed in a certain proportion from oleic acid and oleylamine. During ball milling, the ball-to-material ratio is 10:1, i.e. 1 g of high-entropy oxide powder is added to each ball mill tank, 10 g of grinding balls (3 large balls with a diameter of 12 mm, 5 medium balls with a diameter of 8 mm, and 10 small balls with a diameter of 6 mm), and 2 mL of n-heptane is added to completely dissolve 0.87 mL of oleic acid and 0.91 mL of oleylamine surfactant. After ball milling for 18 h, a large amount of ethanol is added to the ball mill tank for flushing, and the black suspension washed out is transferred to a beaker. After standing for 30 min, the solution is layered, and the supernatant is poured out. This process is repeated 5-7 times until the supernatant is clear, not yellowish, and not acidic. At this point, the washing is complete, and the sample can be directly taken out.

[0105] The catalyst sample is placed in a reactor, and 40 ppm of o-xylene, 5 vol.% of O2, and N2 carrier gas are introduced under the conditions of a reaction temperature of 200-450°C and an airspeed of 30000 h -1 -1. The catalytic efficiency for o-xylene is 32.19% to 73.58%, and under the condition of additionally introducing 5 vol.% of H2O into the flue gas, the catalytic efficiency for o-xylene is 32.64% to 71.87%.

[0106] The results of Example 8 and Comparative Example 2 are plotted in a graph, as shown in Figure 8 By comparison, it can be found that the water resistance of the two catalysts treated by ball milling is significantly improved, and the high-entropy catalyst has a large increase in specific surface area, exposing active sites, and showing water promotion phenomenon.

[0107] Example 11

[0108] The sample (Example 18) treated by ball milling for 18 h with 15% surfactant is placed in a reactor, and 50 ppm of o-xylene, 200 ppm of NO, 50 ug / m -1 -1. Hg, 5 vol.% of O2, and N2 carrier gas are introduced under the conditions of a reaction temperature of 200-450°C and an airspeed of 30000 h 3 -1.

[0109] The catalytic effect of each pollutant is shown in Figure 9 . Figure 9Among them, OCE refers to VOC catalytic efficiency, NCE refers to nitrogen oxide catalytic efficiency, HgCE refers to Hg removal efficiency, (x) indicates that the gas environment is except oxygen and nitrogen, i.e. OCE(VOC+NO) refers to the catalytic efficiency of VOC when VOC and nitrogen oxide are removed jointly. The experimental results show that the efficiency difference is not large when VOC, nitrogen oxide, Hg and joint removal are removed alone, and the efficiency decrease is controlled within 5%, and the joint removal of NO and VOC even appears a certain efficiency increase. It is shown that the present application can complete the joint removal of nitrogen oxide and mercury vapor without affecting the removal of volatile organic pollutants.

[0110] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. Use of a high-entropy oxide catalyst in catalyzing the oxidation of volatile organic pollutants in flue gas from coal combustion, characterized in that, The preparation method of the high-entropy oxide catalyst comprises the following steps: dissolving the precursors corresponding to the metal elements and a combustion-supporting agent into water to obtain a dissolving solution; removing water in the dissolving solution to obtain a high-entropy oxide precursor; the metal elements are Mn, Ce, Fe, Co and Cr; performing calcination and quenching on the high-entropy oxide precursor to obtain the high-entropy oxide catalyst; the quenching is water quenching; after the quenching, the obtained high-entropy oxide is mixed with a surfactant solution for ball milling; the mass of the surfactant in the surfactant solution is 5-50% of the mass of the high-entropy oxide; the temperature of the calcination is 1000-1200℃; The high-entropy oxide has a specific surface area of 1.5 to 6 m 2 / g.

2. Use according to claim 1, characterized in that, the coal-fired flue gas contains remaining pollutants, and the remaining pollutants include one or more of mercury vapor, nitrogen oxide, water vapor and sulfur oxide.

3. Use according to claim 1, characterized in that, the combustion-supporting agent includes one or more of glycine, urea and citric acid.

4. Use according to claim 1, characterized in that, the time of the calcination is 20-40 min.

5. The use according to claim 1, characterized in that, the time of the ball milling is more than 6 h.

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