A method for catalytic oxidation of carbon monoxide based on a plasma hydroxylated high-entropy metal oxide catalytic material

Abstract

The application discloses a method for catalytic oxidation of carbon monoxide based on plasma hydroxylated high-entropy metal oxide catalytic material, and belongs to the technical field of flue gas treatment. The high-entropy metal oxide catalytic material is filled in a discharge cavity of a plasma reactor, carbon monoxide flue gas is introduced into the discharge cavity, and high-voltage discharge catalytic oxidation reaction is carried out to convert carbon monoxide into carbon dioxide. The method utilizes plasma discharge ionization of water vapor to form a large number of hydroxyl sites on the surface of the high-entropy metal oxide catalytic material to occupy oxygen vacancies, and the hydroxyl sites can promote the decomposition of O3 into active oxygen in the discharge cavity to efficiently oxidize and remove CO components in the flue gas. Meanwhile, the hydroxyl sites and SO2 are acidic components and repel each other, so that the oxygen vacancies are prevented from adsorbing SO2 and being poisoned, the efficiency and stability of the high-entropy metal oxide catalytic material in catalytic oxidation of CO in a humid sulfur-containing sintering flue gas environment are improved, and the method is particularly suitable for treatment of industrial complex flue gas.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for oxidizing carbon monoxide, in particular to a method for catalytically oxidizing carbon monoxide based on plasma hydroxylated high-entropy metal oxide catalytic material, belonging to the technical field of flue gas treatment. BACKGROUND

[0002] CO in sintering flue gas of the steel industry causes serious harm to the environment, and needs to be treated by flue gas decarburization. The mainstream process of existing flue gas decarburization treatment is metal catalytic oxidation process, but the existing transition metal catalysts generally have defects such as insufficient catalytic activity below 200 DEG C, poor water resistance and poor sulfur resistance.

[0003] Recently, there have been reports of removing carbon monoxide in flue gas by coupling plasma discharge with catalytic oxidation, which can overcome the above-mentioned defects of existing transition metal catalysts. For example, Chinese Patent Application (Application Publication No. CN117205749A) discloses filling a copper-manganese co-oxide catalyst containing oxygen vacancies into the discharge cavity of a plasma reactor, and then passing flue gas into the discharge cavity for discharge catalytic oxidation to remove carbon monoxide components in the flue gas. This method realizes the perfect coupling of the advantages of plasma discharge and metal oxide catalytic oxidation processes, greatly improves the selectivity and efficiency of the carbon monoxide oxidation reaction in the flue gas, and prolongs the service life of the catalyst and the discharge equipment, reduces the energy consumption and treatment cost of the flue gas, and realizes clean production. Although the copper-manganese co-oxide catalyst coupled with the plasma system can adapt to the humid flue gas environment, it is difficult to adapt to the humid flue gas environment containing sulfur dioxide. The main reason is that in a humid environment, carbonate is mainly deposited on the surface of the catalyst, and when SO2 is present in the environment, the catalyst surface poisoning is mainly due to the deposition of sulfate on the surface of the catalyst. The structural stability of sulfate is much better than that of carbonate, so it is difficult to completely break through its surface covering layer by the impact of high-energy particles of plasma, and long-term use will inevitably cause irreversible deactivation of the catalytic material. In addition, the literature (“High entropy oxides-exploring a paradigm of promising catalysts: A review”, Albedwawi S H, et al., Materials & Design, 2021, 202: 109534) discloses that high-entropy metal oxides (HEOs) exhibit higher low-temperature catalytic oxidation activity than medium- and low-entropy metal oxides, and have become a new direction for CO catalyst design. Although HEOs show potential in the field of CO low-temperature catalysis, their practical application still faces the challenge of insufficient sulfur resistance. Especially in a humid and sulfur dioxide-containing flue gas environment, when the reaction time reaches more than 100 h, the activity easily decreases significantly. This is mainly because SO2 is adsorbed on the surface of HEOs and occupies their active sites, and the product sulfate continuously accumulates to form a covering layer to isolate the catalyst from the reaction gas. Although the surface reaction sites of HEOs are more dense and the high-entropy structure is more stable, the catalytic activity can only be maintained for about 24 h. When the flue gas is passed for more than 30 h, the high-entropy metal oxide still cannot resist the continuous erosion of SO2 for a long time, thereby affecting its catalytic performance. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for catalytic oxidation of carbon monoxide based on plasma hydroxylated high-entropy metal oxide catalytic material, which utilizes plasma discharge ionization of water vapor to form hydroxyl sites on the surface of high-entropy metal oxide catalytic material to occupy oxygen vacancies, and these hydroxyl sites can promote the decomposition of O3 into active oxygen in the plasma discharge cavity to efficiently remove CO components in flue gas, and at the same time, the hydroxyl groups occupy the oxygen vacancies on the surface of high-entropy metal oxide catalytic material in advance, and the hydroxyl sites and SO2 are acidic components and repel each other, which avoids the poisoning of oxygen vacancies by adsorbing SO2, improves the efficiency and stability of high-entropy metal oxide catalytic material in catalytic oxidation of CO in humid sulfur-containing sintering flue gas environment, and is particularly suitable for treatment of industrial complex flue gas.

[0005] In order to achieve the above technical purpose, the present application provides a method for catalytic oxidation of carbon monoxide based on plasma hydroxylated high-entropy metal oxide catalytic material, which fills high-entropy metal oxide catalytic material in the discharge cavity of a plasma reactor, and passes carbon monoxide flue gas into the discharge cavity for high-voltage discharge catalytic oxidation reaction to convert carbon monoxide into carbon dioxide;

[0006] The high-entropy metal oxide catalytic material is a co-oxide of copper, manganese, cerium, cobalt and vanadium, and has a hydrophilic modification on the surface;

[0007] The carbon monoxide flue gas contains carbon monoxide, sulfur dioxide and water vapor.

[0008] The existing copper-manganese co-oxide catalyst coupled with a plasma discharge body system mainly relies on oxygen vacancies to combine O2 molecules in air to achieve catalytic oxidation of CO, but Cu and Mn elements have natural affinity for SO2, which easily forms sulfate structures to occupy active sites and cause catalyst deactivation. The key of the application is to use a high-entropy metal oxide catalyst material coupled with a plasma discharge body system to achieve catalytic oxidation of carbon monoxide in flue gas. Through the synergistic effect of multiple transition metal species in the high-entropy metal oxide catalyst material, it has high catalytic oxidation CO activity and stability, among which Cu and Mn elements mainly provide oxygen vacancy active sites, V element is slightly acidic and helps to improve the sulfur resistance of the material, Co can form Co2(CO)8 carbonyl compounds to facilitate the surface adsorption of CO gas molecules, and the large atomic size of Ce atoms embedded in the lattice causes lattice distortion effect, so that the sulfate cannot form a symmetrical structure on the surface to stably combine, promoting the reversible decomposition of the sulfate. Compared with the existing copper-manganese co-oxide catalyst coupled with a plasma system, the high-entropy metal oxide catalyst material coupled with a plasma system has excellent sulfur resistance, higher catalytic stability and longer service life during catalytic oxidation of carbon monoxide: on the one hand, the high-entropy metal oxide catalyst material has a high-entropy structure, which is stable and can withstand the impact of high-pressure discharge while maintaining structural stability; on the other hand, the synergistic effect of multiple transition metals introduced by the high-entropy metal oxide catalyst material makes the stability of the sulfate formed on the surface decrease sharply or even reversibly decompose at low temperature, thereby converting irreversible deactivation into reversible deactivation; thirdly, the high-entropy metal oxide catalyst material is treated by surface hydrophilic modification, which can effectively improve its wettability and more efficiently combine the hydroxyl radicals formed by the ionization of H2O, these hydroxyl radical sites occupy the oxygen vacancies on the surface of the catalyst and exhibit acid activity, which repels SO2, which belongs to the same acid component, from being adsorbed on the surface of the catalyst, thereby giving the catalyst good sulfur resistance, and the active hydroxyl radical sites can also promote the decomposition of O3 to produce active oxygen, which is used for catalytic oxidation of CO, thereby improving the oxidation rate of CO in a low-temperature environment.

[0009] The reaction principle of the high-entropy metal oxide catalyst material used in the application for realizing carbon monoxide oxidation in a plasma discharge environment is as follows: H2O and O2 in flue gas are ionized by high-speed collision of free electrons, the hydroxyl radicals formed by water ionization are coordinated with metal ions in the oxygen vacancies on the surface of the catalyst to form active hydroxyl radical sites, O2 is converted into O3, and active oxygen is produced under the catalytic promotion of the active hydroxyl radical sites to improve the catalytic conversion efficiency of CO (Co 2+ and Mn 2+ are taken as examples):

[0010] nH2O+e→nH + +nOH - ;

[0011] Mn 2+ +xOH - →[Mn(OH) x ] (2-x)+ ;

[0012] Co 2+ +xOH - →[Co(OH) x ] (2-x)+ ;

[0013] After the unsaturated metal oxygen vacancy combines with the hydroxyl to form an active hydroxyl site, the surface is treated with acid to resist SO2 invasion:

[0014] O3+Mn-OH→Mn-OH--O δ- -O=O→Mn-OH+[O]+[O2];CO+[O]→CO2;

[0015] O3+Co-OH→Co-OH--O δ- -O=O→Co-OH+[O]+[O2];CO+[O]→CO2;

[0016] O3 is induced to decompose on the active hydroxyl site of the surface of the catalyst to form O2 molecules and active oxygen [O], and the active oxygen [O] can promote the oxidative conversion of CO, while the O2 molecules return to the air to accept ionization and recombination again to form the O3 product, completing the catalytic cycle. The hydroxyl site is used to replace the oxygen vacancy as the active oxygen combination and reaction site, and O3 is used to replace O2 as the main oxygen source for the catalytic oxidation of CO.

[0017] In the existing copper-manganese co-oxide catalyst coupled plasma system catalytic oxidation of carbon monoxide in flue gas, it is difficult to generate a large number of hydroxyl sites in the oxygen vacancies on its surface, and it is easier to adsorb sulfur dioxide to form sulfates, and it is difficult to realize the reversible conversion of sulfates, so it is difficult to maintain sustained and stable catalytic activity. The high-entropy metal oxide catalytic material coupled plasma system can generate a large number of hydroxyl sites in the oxygen vacancies on its surface, not only has an SO2 exclusion effect, but also can catalytically decompose O3 produced by the plasma source to realize the oxidation of carbon monoxide in flue gas, showing higher catalytic activity and sulfur resistance, and being more suitable for complex flue gas treatment.

[0018] As a preferred scheme, the content of each metal oxide in the high-entropy metal oxide catalytic material is not more than 25% of the total moles of each metal oxide.

[0019] As a preferred scheme, the CO concentration in the carbon monoxide flue gas is 0.8-1.0 vol%, the water vapor concentration is 5-10 vol%, the SO2 concentration is not higher than 50 ppm, and the flue gas temperature ranges from normal temperature to 250 DEG C. The flue gas is a by-product discharged at the end of sintering production and the like of a steel plant. Generally, the higher the concentrations of sulfur dioxide and water vapor in the flue gas, the greater the influence on the high-entropy metal oxide catalytic material, and the high-entropy metal oxide catalytic material of the present application makes full use of the hydroxyl generated by the plasma ionization of water vapor to modify the high-entropy metal oxide catalytic material, endows it with higher catalytic activity and sulfur resistance, and can adapt to the treatment of higher concentration of sulfur dioxide and humid flue gas.

[0020] As a preferred scheme, the high-entropy metal oxide catalytic material is prepared by the following method: copper salt, manganese salt, cerium salt, cobalt salt and vanadium salt and dispersant are added to water to dissolve and mix uniformly, then excess precipitant is added to carry out coprecipitation reaction to obtain a solid-liquid mixture; the solid-liquid mixture is subjected to hydrothermal reaction, after the completion of the hydrothermal reaction, rapid cooling is carried out, and the hydrothermal reaction solid product is separated out; the solid product is calcined to obtain high-entropy metal oxide, and the high-entropy metal oxide is subjected to surface hydrophilic modification to obtain the high-entropy metal oxide catalytic material.

[0021] In the preparation process of the high-entropy metal oxide catalytic material of the present application, the dispersing effect of the dispersant is first utilized to realize the high dispersion of metal ions, to ensure that a plurality of metal ions maintain a highly uniform dispersion state during coprecipitation, and to prevent the phase separation problem caused by the difference in hydrolysis rate of different metal ions; on this basis, the addition of excess precipitant can ensure that the solution system is in an alkaline environment and reaches the critical value of coprecipitation of a plurality of metal ions, which is conducive to the formation of uniform nanocrystalline nuclei; the nanocrystalline nuclei realize growth under the high temperature and high pressure conditions of hydrothermal reaction; the wrapping effect of the dispersant can limit the excessive growth of crystals to obtain nanometer size during the growth of the nuclei; and the induction effect of the dispersant realizes the ordered crystallization of metal oxides to grow into sheet-shaped nanostructures with special morphology; after the completion of the hydrothermal reaction, rapid cooling is carried out, which is more likely to maintain the uniform state of phase mixing than slow cooling, to prevent the occurrence of segregation due to the fact that the configuration entropy is not stronger than the mixing enthalpy during the cooling process, and to prevent the adverse effects of secondary phases; and the hydrothermal product is further treated by high-temperature calcination to improve the crystal structure of the metal oxide and improve the stability. It should be noted that, due to the poor hydrophilicity of the high-entropy metal oxide, it is difficult to adsorb water vapor to generate a large number of hydroxyl sites in the oxygen vacancies on its surface, and the present application is subjected to hydrophilic modification on its surface, which is conducive to the generation of a large number of hydroxyl sites on the surface of the high-entropy metal oxide.

[0022] As a more preferred scheme, the copper salt includes at least one of CuSO4, Cu(NO3)2 and CuCl2.

[0023] As a more preferred solution, the manganese salt comprises at least one of MnSO4, Mn(NO3)2, MnCl2.

[0024] As a more preferred solution, the cerium salt comprises at least one of Ce(NO3)3, Ce2(C2O4)3, Ce(C8H 15 O2)3.

[0025] As a more preferred solution, the cobalt salt comprises at least one of CoSO4, Co(NO3)2, CoCl2.

[0026] As a more preferred solution, the vanadium salt comprises at least one of Na3VO4, NH4VO3, VOSO4.

[0027] The copper salt, manganese salt, cerium salt, cobalt salt and vanadium salt involved in the present application are all conventional water-soluble metal salts.

[0028] As a preferred solution, the dispersant comprises at least one of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol. The preferred dispersant of the present application all contains a large number of electron-rich heteroatoms, which can complex with transition metal ions. Further, polyvinylpyrrolidone is preferred as the dispersant, which contains pyrrolidone groups capable of coordinating with high-valence metal ions, which is conducive to promoting the dispersion of metal ions, and at the same time, it can be adsorbed on the surface of metal oxide crystal nucleus to induce the ordered growth of crystals and improve the crystallization performance.

[0029] As a more preferred solution, the amount of the dispersant is 0.3-1 times the total molar amount of the copper salt, manganese salt, cerium salt, cobalt salt and vanadium salt. If the amount of the dispersant is too low, it is not conducive to the dispersion of metal ions, which can cause the agglomeration of nanoparticles in the subsequent precipitation process, and at the same time, if the dispersion of multiple metal ions is uneven during co-precipitation, phase separation can occur due to the difference in hydrolysis rate of metal ions.

[0030] As a preferred solution, the base precipitant comprises at least one of urea, sodium hydroxide, ammonia water. The most preferred base precipitant is urea. Compared with sodium hydroxide, the decomposition product of urea is gas, which will not leave metal ions or other impurities. Compared with ammonia water, solid urea is stable in state, which avoids the pH fluctuation caused by the volatilization of ammonia component.

[0031] As a preferred solution, the amount of the base precipitant is 6-10 times the total molar amount of the copper salt, manganese salt, cerium salt, cobalt salt and vanadium salt. The excess base precipitant can ensure that the solution system is in an alkaline environment until the critical value of co-precipitation of multiple metal ions is reached. It should be noted that the precipitant is preferably added slowly to avoid uneven nucleation caused by local supersaturation.

[0032] As a preferred scheme, the hydrothermal reaction is carried out at a temperature of 160-200℃ for 8-12h. The hydrothermal reaction conditions affect the catalytic activity of the high-entropy metal oxide catalytic material. As the temperature of the hydrothermal reaction gradually increases, the catalytic activity of the catalyst gradually increases. When the hydrothermal temperature reaches 180℃, the high-entropy metal oxide catalytic material exhibits the best catalytic activity. Further increasing the hydrothermal reaction temperature does not significantly increase the catalytic activity of the high-entropy metal oxide catalytic material. This indicates that too high or too low hydrothermal reaction temperature will adversely affect the catalytic performance of the high-entropy metal oxide catalytic material. The optimal hydrothermal reaction temperature range is 160-200℃.

[0033] As a preferred scheme, the quenching is carried out by water cooling. Compared with other cooling methods such as air cooling, water cooling has a faster cooling speed. Quenching is more likely to maintain a uniform state of phase mixing than slow cooling, preventing the occurrence of segregation due to the fact that the configurational entropy is not higher than the mixing enthalpy during the cooling process, and producing the adverse effects of secondary phases.

[0034] As a preferred scheme, the calcination is carried out at a temperature of 400-600℃ for 4-6h. At a suitable calcination temperature, the product of the hydrothermal reaction can lose crystal water and reorganize the phase to convert into stable metal oxides, thereby strengthening the interaction between the metal oxides. At the same time, the calcination process can oxidize and decompose to remove organic matter, thereby avoiding its negative impact on the performance of the material. The calcination temperature can affect the structure and performance of the high-entropy metal oxide catalytic material. If the temperature is too low, the crystallinity is low, which may result in incomplete conversion of some precursors into stable lattice structure metal oxides. If the temperature is too high, Ostwald ripening effect leads to particle coarsening, and even element segregation. Preferably, the high-entropy metal oxide catalytic material system is calcined at a temperature of 400-600℃, which can achieve a balance between high crystallinity and controllable morphology.

[0035] As a preferred scheme, the process of hydrophilic modification is that a solution containing a hydrophilic organic small molecule is coated on the surface of the high-entropy metal oxide and then dried.

[0036] As a preferred scheme, the hydrophilic organic small molecule includes at least one of catechol, gallic acid, and tannic acid.

[0037] As a preferred scheme, the amount of the hydrophilic organic small molecule is 0.5-0.1 times the total molar amount of copper salt, manganese salt, cerium salt, cobalt salt, and vanadium salt.

[0038] The surface hydrophilic modification treatment process of the high-entropy metal oxide of the present application is as follows: at least one of catechol, gallic acid and tannic acid is dissolved in an ethanol solution (mass concentration 5% to 10%), and then coated on the surface of the high-entropy metal oxide. The amount of the organic molecules is controlled to be 0.5 to 0.1 times the total molar amount of copper salt, manganese salt, cerium salt, cobalt salt and vanadium salt. After the ethanol solution containing the hydrophilic organic small molecules is coated on the surface of the high-entropy metal oxide, it is placed in an environment not higher than 100 DEG C for evaporation and drying, so that the ethanol is volatilized and removed while the structure of the organic molecules is not damaged.

[0039] As a preferred scheme, the mass of the high-entropy metal oxide catalytic material is proportional to the flow of carbon monoxide flue gas; the mass space velocity of the flue gas is 25 to 35 m 3 / (h x kg).

[0040] As a preferred scheme, the conditions of the high-voltage discharge are as follows: the voltage is 10 to 30 kV, and the discharge frequency is 1 to 10 kHz.

[0041] Compared with the prior art, the technical scheme of the present application has the following beneficial technical effects:

[0042] The high-entropy metal oxide catalytic material of the present application realizes the catalytic oxidation reaction of CO in the humid sulfur-containing flue gas by coupling with the plasma high-voltage discharge, and exhibits high efficiency and durability, and can be used for the oxidation removal of the CO component in the flue gas of the steel industry. The existing copper-manganese co-oxide catalyst coupled with the plasma system has good stability, and the main principle is to use the high-energy particle impact to break the carbonate covering layer generated in the humid environment of the copper-manganese co-oxide catalytic material. Although it can adapt to the humid flue gas environment, it cannot adapt to the humid flue gas environment containing sulfur dioxide. The main reason is that only carbonate by-products are deposited on the surface in the humid environment, and when SO2 exists in the environment, the surface poisoning is mainly caused by the deposition of sulfate rather than carbonate, and the structural stability of the sulfate is much better than that of the carbonate, so it is difficult to completely break the surface covering layer by the impact of the high-energy particles of the plasma. Irreversible deactivation of the catalytic material is inevitable during long-term use. The high-entropy metal oxide catalytic material of the present application can weaken the surface adsorption strength of SO2 by surface hydroxyl treatment and reduce the structural stability of the sulfate product by introducing large-size transition metals into the high-entropy metal oxide catalytic material, so that it can maintain high sulfur resistance while maintaining the catalytic oxidation activity of CO.

[0043] The high-entropy metal oxide catalytic material of the application realizes catalytic oxidation of CO in humid sulfur-containing flue gas by coupling plasma high-voltage discharge, and the CO conversion rate remains > 90% after 100h of reaction in an environment containing 10vol% H2O and 50ppm SO2. Even in a complex flue gas containing water and sulfur, the CO concentration can be reduced to below 1000ppm after catalytic oxidation by the high-entropy metal oxide coupled with plasma, with a removal efficiency of > 90%. Under the same experimental conditions, the catalytic efficiency of Cu-Mn-Ce-Co-V five-element mixed metal oxide without plasma coupling is reduced to 84% after 100h of reaction in the same environment.

[0044] The high-entropy metal oxide catalytic material of the application contains only transition metal components and can achieve excellent catalytic effect on CO components in humid sulfur-containing low-temperature flue gas.

[0045] The high-entropy metal oxide catalytic material of the application has a high-entropy stable structure and can withstand the discharge impact of high-voltage plasma without causing surface breakage and pore wall collapse. The catalyst surface is hydrophilic, has abundant metal oxygen vacancies that can accept hydroxyl ionization products of water vapor to form acidic active sites, has good sulfur resistance due to the repelling effect on SO2 which is also an acidic gas, and the acidic active sites can be used as a new type of reaction site to decompose O3 to release active oxygen atoms to catalytically convert CO, thereby meeting the requirement of low-temperature catalytic efficiency of CO. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 The mechanism flowchart of catalytic oxidation of carbon monoxide by the high-entropy metal oxide catalytic material of the application through plasma acidification.

[0047] Figure 2 The process flowchart of preparation of the high-entropy metal oxide catalytic material of the application and catalytic oxidation of carbon monoxide by the high-entropy metal oxide catalytic material through plasma acidification.

[0048] Figure 3 The effect comparison chart of the high-entropy metal oxide catalytic material catalytic high-temperature oxidation of carbon monoxide process and the high-entropy metal oxide catalytic material coupled plasma discharge catalytic oxidation of carbon monoxide process; mainly comparing the effects at 30m 3 (kg x h) mass space velocity, humid sulfur-containing flue gas containing 1vol% CO (10vol% H2O, 50ppm SO2) under long-term stability conditions.

[0049] Figure 4 The effect comparison chart of the high-entropy metal oxide catalytic material of the application coupled plasma discharge catalytic oxidation of carbon monoxide process and the copper-manganese co-oxide catalyst containing oxygen vacancies in the prior art; mainly comparing the effects at 30m 3Long-term stability of the reaction under the following conditions: mass hourly space velocity ( / (kg×h)) in moist sulfur-containing flue gas containing 1 vol% CO (10 vol% H2O, 50 ppm SO2, temperature 250℃). Detailed Implementation

[0050] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0051] Example 1

[0052] A steel plant uses (CuMnCeCoV)O2 catalyst to treat CO components in sintering flue gas. The catalyst mass corresponds to a flue gas space velocity of 30 m / s². 3 / (kg×h), flue gas containing 1vol%CO, 7vol%CO2, 15vol%O2, 10vol%H2O, and 50ppmSO2 (temperature 250℃), filled with N2 gas.

[0053] This high-entropy metal oxide catalyst was prepared via hydrothermal synthesis: Cu(NO3)2, Mn(NO3)2, Ce(NO3)3, Co(NO3)2, and NH4VO3 precursors were mixed in equimolar proportions and dissolved in water at 60°C with stirring to form a homogeneous metal ion solution with an average concentration of 0.1 mol / L. PVP dispersant was then added and stirring continued; 1 mol of metal ions corresponded to 0.3 mol (33.3 g) of PVP. After the solution became clear, excess urea was slowly added dropwise, with the total amount being 6 times the total molar amount of metal ions. The resulting solid-liquid mixture was transferred to a hydrothermal reactor and reacted at 180°C for 8 hours, followed by water cooling for 6 hours. The resulting solid-liquid mixture was filtered and washed, and the intermediate powder product was calcined at 500°C for 5 hours to obtain the high-entropy metal oxide (HEOs). After the HEOs surface is coated with a 5% ethanol aqueous solution containing catechol, it is dried at 100℃ for 12h to obtain the final product, high-entropy metal oxide catalyst material. The total molar amount of catechol is 0.5 times the total molar amount of metal ions.

[0054] HEOs catalyst is filled into the plasma discharge chamber, and the flue gas is introduced for catalytic oxidation. The applied voltage is 30kV and the discharge frequency is 5kHz.

[0055] The reaction principle is as follows Figure 1As shown: air is ionized to release electrons, and the electrons are driven by a high-voltage electric field to run at high speed. The high-speed free electrons collide with H2O to ionize and form hydroxyl radicals (-OH) which bind to the surface vacancies of the metal catalyst to complete the surface acidification treatment. The hydroxyl structure instead of oxygen vacancies is conducive to repelling SO2 which is also an acidic gas, and the sulfur resistance of the material is enhanced. In addition, the terminal hydrogen ions of the hydroxyl structure are in an electron-deficient state, and are easy to attract ozone which is also an ionization product. The electron-excessive ozone is easy to be decomposed by the hydroxyl radical site to form an O2 molecule and an active oxygen atom [O], which is used for catalytic oxidation of CO. This reaction path can only exist in a discharge environment that can continuously and stably produce ozone, and the hydroxyl surface acidification treatment of the metal site also takes into account the CO catalytic activity and sulfur resistance of the HEOs, thereby effectively improving the low-temperature conversion rate of CO and the long-term stability of the HEOs in the flue gas environment. The conversion rate of CO after 100h of reaction still reaches more than 94%.

[0056] Control group 1

[0057] The (CuMnCeCoV)O2 used as the control group also used the above method to prepare the material. However, no low-temperature plasma discharge assistance was performed. The HEOs material was subjected to CO catalytic oxidation alone under the conditions of no H2O and containing 10vol% H2O, and the remaining flue gas conditions were unchanged. The catalytic efficiency stability and the catalytic results of the above catalyst-low-temperature plasma coupling system were compared. The results show that after the same reaction for 100h, the conversion rate of CO in the coupling system still reaches more than 94%, while the conversion rate of CO in the dry environment using HEOs alone is reduced to less than 90%, and the conversion rate of CO in the humid environment is further reduced to 84%. The CO catalytic stability is significantly lower than that of the coupling system.

[0058] Control group 2

[0059] The copper-manganese co-oxide catalyst containing oxygen vacancies was prepared by the coprecipitation method according to the patent application (publication number CN117205749A) example 2.

[0060] The copper-manganese co-oxide catalyst containing oxygen vacancies was replaced with the HEOs prepared in example 1 and filled into the plasma discharge cavity. The flue gas catalytic oxidation in example 1 was carried out, and the voltage applied was 30kV and the discharge frequency was 5kHz.

[0061] The experimental results are as follows Figure 4As shown, it can be seen that the existing copper-manganese co-oxide catalyst coupled with the plasma system has low efficiency and poor stability in catalyzing the oxidation of carbon monoxide, and the conversion efficiency of carbon monoxide has decreased to less than 10% at 70h, while the HEOs coupled with the plasma system prepared in Example 1 can still maintain a carbon monoxide conversion efficiency of more than 90% for 100h.

[0062] Therefore, it is illustrated that the copper-manganese co-oxide catalyst coupled with the plasma system is not suitable for the humid and sulfur dioxide-containing flue gas environment. The main reason is that if there is no sulfur dioxide in the environment, the catalyst surface poisoning is mainly caused by the deposition of carbonates, and when there is SO2 in the environment, the catalyst surface poisoning is mainly caused by the deposition of sulfates rather than carbonates. The structure stability of sulfates is much better than that of carbonates, so it is difficult to completely break the surface cover layer by the impact of high-energy particles of the plasma, and irreversible deactivation of the catalytic material is still unavoidable. The HEOs coupled with the plasma system greatly increases the initial sites of hydroxyl chemical adsorption based on the high defect density and high activity of the high-entropy oxide surface, so that it can more efficiently dissociate and adsorb water molecules, and convert the physically adsorbed water into chemically adsorbed hydroxyl, and the surface oxygen vacancies are more occupied by hydroxyl. Unlike oxygen vacancies, hydroxyl sites have a repelling effect on SO2 which is also acidic. Before SO2 reaches the catalyst surface, a high-density hydroxyl layer has occupied a large number of active metal sites, forming a physical and chemical barrier. Abundant hydroxyl can guide the adsorbed SO2 to generate soluble bisulfite (HSO3 - ) and be desorbed by the impact of high-energy particles in the discharge system, rather than generating solid-state sulfate (SO4 2- ) which is difficult to remove. In addition, the plasma environment can continuously generate O3, which is used to decompose O3 to produce O2 gas molecules and an [O] active oxygen atom for CO catalytic conversion. The decomposition product O2 gas molecule can be converted into O3 again in the discharge environment to repeat the above decomposition and release of active oxygen to convert CO. The SO2-resistant hydroxyl site replaces the oxygen vacancy which has no sulfur resistance and becomes the active oxygen formation and reaction site. This takes into account the sulfur resistance and CO catalytic activity. Therefore, unlike the traditional copper-manganese co-oxide catalyst coupled with the plasma, the HEOs coupled with the plasma system has high sulfur resistance while maintaining the activity of CO oxidation due to the particularity of the reaction site and oxygen source.

[0063] Example 2

[0064] A steel plant uses (CuMnCeCoV)O2 catalytic material to treat CO components in sintering flue gas. The flue gas temperature is 120°C, the filling amount of the catalyst inside the reactor is about 1 kg, the mass space velocity is controlled at 25 m 3 / (kg x h), including 1 vol% CO, 10 vol% CO2, 10 vol% O2, 10 vol% H2O, 30 ppm SO2, and filling gas N2.

[0065] Manganese nitrate monohydrate, copper nitrate pentahydrate, cerium nitrate hexahydrate, cobalt nitrate hexahydrate, and ammonium metavanadate precursor are mixed in equal molar ratio, and a metal ion solution with an average concentration of 0.1 mol / L is formed by stirring and dissolving at 60°C. Then, PVP dispersant is added for continuous stirring. For 1 mol of metal ions, 0.3 mol of PVP dispersant, i.e. 33.3 g, is added. After the solution becomes clear, an excess of solid urea 6 times the total metal ion molar amount is added drop by drop. The obtained solid-liquid mixture is transferred into a hydrothermal reactor and reacted under hydrothermal conditions at 180°C for 8h, and then water-cooled for at least 5h. The obtained powder product is washed after filtration, calcined at 500°C for 5h to obtain a high-entropy metal oxide. The high-entropy metal oxide is coated with a 10% gallic acid ethanol solution on the surface, and then dried at 100°C for 24h to obtain the final product, a high-entropy metal oxide catalyst material. The total molar amount of gallic acid is equal to the total molar amount of metal ions.

[0066] The high-entropy metal oxide catalyst material is filled into a plasma discharge reaction chamber, and the above flue gas is introduced for catalytic oxidation.

[0067] In order to compare the effects of different applied voltages on the CO reaction activity of HEOs materials, the sample is divided into five parts, and an external voltage of 10kV, 15kV, 20kV, 25kV, and 30kV is applied respectively. The discharge frequency is fixed at 5kHz. All samples are continuously reacted at 120°C for 24h under the condition of 10vol%H2O-30ppmSO2, and the effects on CO catalytic efficiency are compared. The initial concentration of CO is about 1vol%. It is finally found that the CO catalytic efficiency increases with the increase of voltage in the range of 10~25kV, and the CO conversion rates are 79%, 84%, 89%, and 94% respectively. While further increasing to 30kV, the CO conversion rate increases to 95%, and the increase is not obvious. The CO conversion rate can be maintained stable after 24h of experiment. This shows that if the applied voltage is too high, the energy utilization efficiency will decrease, and the best external voltage is 25kV.

[0068] Example 3

[0069] A steel plant relies on a fluidized bed continuous device composed of catalyst filled in the reactor for CO removal. The unit catalyst corresponds to a flue gas flow of 35 m 3(kg x h). The (CuMnCeCoV)O2 high-entropy metal oxide catalyst was prepared by a hydrothermal synthesis method. During the synthesis of the high-entropy metal oxide, the synthesis steps of the corresponding intermediate powder product refer to Example 1.

[0070] The CO catalytic bed was used to treat 1 vol% CO at 120°C in the presence of 10 vol% H2O and 50 ppm SO2 flue gas. The HEOs were filled in the discharge chamber and subjected to high-voltage discharge with an external low-temperature plasma device. The discharge voltage was fixed at 20 kV, and the discharge frequency was set at 1 kHz, 2 kHz, and up to 10 kHz. The CO removal efficiency of the HEOs in the same flue gas environment was compared at different discharge frequencies.

[0071] The results show that under the discharge conditions of 1-5 kHz, the corresponding CO conversion rates are 56%, 65%, 76%, 84%, and 93%, respectively. When the discharge frequency is further increased, the CO conversion rates corresponding to 6-10 kHz are 94%, 95%, 95%, 96%, and 96%, respectively, and the efficiency does not increase significantly. After 24 h of reaction in several groups of experiments, the conversion rates can remain stable, and the water poisoning and sulfur poisoning phenomena on the surface of the catalyst change from irreversible to reversible, greatly extending the working life of the catalyst in the sintering flue gas. However, if the discharge frequency is too high, the energy utilization efficiency will decrease, and the optimal discharge frequency is 5 kHz.

[0072] The above only describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above examples. Improvements and changes made by those skilled in the art without departing from the technical concept of the present application should also be considered as falling within the protection scope of the present application.

Claims

1. A method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of high-entropy metal oxide catalytic materials, characterized in that: High-entropy metal oxide catalytic material is filled into the discharge chamber of a plasma reactor, and carbon monoxide flue gas is introduced into the discharge chamber to carry out a high-voltage discharge catalytic oxidation reaction to convert carbon monoxide into carbon dioxide. The high-entropy metal oxide catalytic material is a co-oxide of copper, manganese, cerium, cobalt and vanadium, and its surface is hydrophilic modified. The carbon monoxide flue gas contains carbon monoxide, sulfur dioxide, and water vapor.

2. The method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of high-entropy metal oxide catalytic materials according to claim 1, characterized in that: The content of each metal oxide in the high-entropy metal oxide catalytic material does not exceed 25% of the total molar amount of each metal oxide.

3. The method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of high-entropy metal oxide catalytic materials according to claim 1, characterized in that: The CO concentration in the carbon monoxide flue gas is 0.8~1.0 vol%, the water vapor concentration is 5~10 vol%, the SO2 concentration is not higher than 50 ppm, and the flue gas temperature range is room temperature to 250℃.

4. The method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of high-entropy metal oxide catalytic materials according to claim 1, characterized in that: The high-entropy metal oxide catalytic material is prepared by the following method: copper salt, manganese salt, cerium salt, cobalt salt, vanadium salt and dispersant are dissolved and mixed evenly in water, and then excess alkaline precipitant is added to carry out a co-precipitation reaction to obtain a solid-liquid mixture; the solid-liquid mixture is subjected to a hydrothermal reaction, and after the hydrothermal reaction is completed, it is rapidly cooled to separate the hydrothermal reaction solid product; The solid product is calcined to obtain a high-entropy metal oxide, and the high-entropy metal oxide is then subjected to surface hydrophilic modification to obtain a high-entropy metal oxide catalytic material.

5. The method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of high-entropy metal oxide catalytic materials according to claim 4, characterized in that: The copper salt includes at least one of CuSO4, Cu(NO3)2, and CuCl2; The manganese salt includes at least one of MnSO4, Mn(NO3)2, and MnCl2; The cerium salts include Ce(NO3)3, Ce2(C2O4)3, and Ce(C8H2O)3. 15 At least one of O2)3; The cobalt salt includes at least one of CoSO4, Co(NO3)2, and CoCl2; The vanadium salt includes at least one of Na3VO4, NH4VO3, and VOSO4; The dispersant includes at least one of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol; The amount of the dispersant is 0.3 to 1 times the total molar amount of copper salt, manganese salt, cerium salt, cobalt salt and vanadium salt; The alkaline precipitant includes at least one of urea, sodium hydroxide, and ammonia water; The amount of the alkaline precipitant used is 6 to 10 times the total molar amount of copper salt, manganese salt, cerium salt, cobalt salt, and vanadium salt.

6. A method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of high-entropy metal oxide catalytic materials according to claim 4 or 5, characterized in that: The hydrothermal reaction conditions are: at a temperature of 160~200℃, the reaction time is 8~12h; The rapid cooling process uses water cooling.

7. A method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of high-entropy metal oxide catalytic materials according to claim 4 or 5, characterized in that: The calcination conditions are: calcination at 400~600℃ for 4~6 hours.

8. A method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of high-entropy metal oxide catalytic materials according to claim 4 or 5, characterized in that: The process of surface hydrophilic modification is as follows: a solution containing hydrophilic organic small molecules is applied to the surface of a high-entropy metal oxide and then dried. The hydrophilic organic small molecules include at least one of catechol, gallic acid, and tannic acid; The amount of the hydrophilic organic small molecule is 0.1 to 0.5 times the total molar amount of copper salt, manganese salt, cerium salt, cobalt salt and vanadium salt.

9. The method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of high-entropy metal oxide catalytic materials according to claim 1, characterized in that: The mass of the high-entropy metal oxide catalytic material is proportional to the flow rate of carbon monoxide flue gas. The mass space velocity of the flue gas is 25-35 m. 3 / (h×kg).

10. A method for catalytic oxidation of carbon monoxide based on plasma hydroxylation of a high-entropy metal oxide catalytic material, as described in claims 1, 2, 3, 4, 5, or 9, characterized in that: The conditions for the high-voltage discharge are: voltage of 10~30kV and discharge frequency of 1~10kHz.

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