Preparation method and application of catalyst for treating chlorinated volatile organic compounds

Abstract

The application provides a preparation method and application of a catalyst for treating chlorine-containing volatile organic compounds, and relates to the technical field of organic waste gas treatment, and comprises the following steps: core-shell structure carrier preparation: preparing a cerium oxide core; coating a yttrium oxide layer, a zirconium oxide layer and a silicon oxide layer on the surface of the cerium oxide core in sequence to obtain a carrier; multi-metal phase active component loading: placing the carrier in hydrogen peroxide water for treatment to obtain a pretreated carrier; adding the pretreated carrier into an ethanol solution, adding citric acid, and performing a reaction by increasing the temperature to obtain a hydroxylated carrier; and loading three cobalt tetroxides and metal palladium on the hydroxylated carrier in sequence to obtain the catalyst. The catalyst has high catalytic activity and stability, and can effectively remove chlorine-containing volatile organic compounds.

Description

Technical Field

[0001] This invention relates to the field of organic waste gas treatment technology, specifically to a method for preparing and applying a catalyst for treating chlorine-containing volatile organic compounds. Background Technology

[0002] Large amounts of chlorinated volatile organic compounds (CVOCs) are often generated in the synthesis of chemicals, pharmaceuticals, coatings, and pesticides. These substances are highly chemically stable, poorly biodegradable, easily accumulate in the environment, and have strong carcinogenic, teratogenic, and mutagenic effects, posing a serious threat to ecosystems and human health. Furthermore, the chlorine element in CVOC molecules is highly electronegative, readily binding to the active sites of catalysts, leading to catalyst poisoning and deactivation, further increasing the difficulty of their remediation.

[0003] Currently, the main treatment methods for chlorinated volatile organic compounds (VOCs) include the following: 1. Incineration: This method is suitable for high-concentration waste gas, but it requires maintaining high temperatures (>800℃), resulting in huge energy consumption. It is also prone to generating dioxins and corrosive HCl, requiring the use of alkaline scrubbing towers and anti-corrosion equipment, which is costly. 2. Adsorption: This method can recover some organic matter, but its adsorption capacity is limited, and it is ineffective in treating low-boiling-point chlorinated VOCs. Furthermore, the adsorbent is frequently regenerated after saturation, which can easily lead to secondary pollution. 3. Catalytic combustion: This method degrades chlorinated VOCs at lower temperatures (200–450℃), resulting in lower energy consumption and widespread application. However, existing catalysts face the following problems: (1) poor resistance to chlorine poisoning; (2) insufficient adaptability to high concentrations: when the waste gas concentration is >6000 mg / Nm³. 3 At high temperatures, the reaction is highly exothermic, leading to catalyst sintering or volatilization of active components. To address these technical problems, existing technologies have improved traditional catalysts. For example, to enhance the catalyst's resistance to chlorine and its stability, some researchers have introduced the noble metal Ru. Ru can enhance the C-Cl bond breaking ability, but it is easily converted into volatile RuCl3 and lost under high humidity conditions. Alkaline earth metals (Ca / Mg) need to be added to stabilize the valence state, increasing costs and still resulting in insufficient high-temperature stability. Other studies have found that introducing non-noble metals such as Mn and vanadium produces catalysts with lower costs, but their oxygen migration efficiency is limited. They are prone to carbon deposition when treating high concentrations of chlorine-containing volatile organic compounds, and their acidic sites have weak ability to remove Cl, leading to chlorine accumulation and deactivation. Therefore, to address these problems, it is necessary to provide a catalyst that combines high activity, strong resistance to chlorine, and high concentration adaptability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a catalyst for treating chlorine-containing volatile organic compounds and its application, which addresses the shortcomings of the existing technology. The catalyst prepared by this method not only has high catalytic activity but also good stability and can effectively remove chlorine-containing volatile organic compounds.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] A method for preparing a catalyst for treating chlorine-containing volatile organic compounds includes the following steps:

[0007] (1) Preparation of core-shell structured carrier:

[0008] Preparation of cerium oxide cores;

[0009] A yttrium oxide layer, a zirconium oxide layer, and a silicon oxide layer are sequentially coated onto the surface of a cerium oxide core to obtain a carrier;

[0010] (2) Loading of multimetallic phase active components:

[0011] The carrier was treated with hydrogen peroxide to obtain a pretreated carrier;

[0012] The pretreated carrier was added to an ethanol solution, citric acid was added, and the mixture was heated to react, yielding a hydroxylated carrier.

[0013] Cobalt tetroxide and palladium metal were sequentially loaded onto a hydroxylation support to obtain a catalyst.

[0014] Preferably, the preparation process of cerium oxide cores includes the following steps:

[0015] A sol is prepared by heating and stirring a mixed solution of cerium nitrate hexahydrate (30-35 wt%), urea, and trisodium citrate.

[0016] The sol was transferred to an autoclave and heated to 115-125℃ for 1 hour. The temperature was then increased to 175-180℃ for 20-22 hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was centrifuged, and the precipitate was washed, dried, and calcined to obtain cerium oxide cores.

[0017] Preferably, the molar ratio of cerium ions, urea and trisodium citrate in the mixed solution is 1:4:(0.15-0.25); the temperature for heating and stirring is 80℃, the stirring speed is 600-800 rpm, and the stirring time is 1-2 hours.

[0018] Preferably, the calcination process for preparing cerium oxide cores is as follows: under an air atmosphere, the temperature is first raised to 550°C at a rate of 2°C / min and held for 1.5-2 hours, then raised to 950°C at a rate of 5°C / min and held for 4.5-5 hours. After calcination, the temperature is cooled to 50°C at a rate of 50°C / min under a nitrogen atmosphere, and then cooled to room temperature with the furnace to obtain the core.

[0019] Preferably, the yttrium oxide coating process includes the following steps:

[0020] Yttrium acetylacetone was dissolved in anhydrous ethanol, then acetylacetone was added, followed by slow dropwise addition of deionized water for hydrolysis to obtain a transparent sol.

[0021] The transparent sol was added to anhydrous ethanol containing cerium oxide, and the mixture was refluxed at 70°C for 3-4 hours under a nitrogen atmosphere. The resulting gel was aged at room temperature for 12 hours and then centrifuged. The precipitate was dried and calcined to obtain cerium oxide / yttrium oxide powder.

[0022] Preferably, the mass ratio of yttrium acetylacetonate, cerium oxide, and deionized water is (0.9-1):10:(0.05-0.08), and the amount of acetylacetonate added is 10-15% of the molar amount of yttrium acetylacetonate; the dropping rate of deionized water is 0.1 ml / min, and hydrolysis is carried out at room temperature for 10-20 min after the addition of deionized water.

[0023] Preferably, the calcination process for preparing cerium oxide / yttrium oxide is as follows: first, the temperature is increased to 300°C at a rate of 1°C / min and held for 1 hour; then, the temperature is increased to 600°C at a rate of 2°C / min and held for 2 hours; finally, the temperature is cooled to room temperature in the furnace to obtain the desired product.

[0024] Preferably, the zirconium oxide coating process includes the following steps:

[0025] Cerium oxide / yttrium oxide powder and polyethylene glycol 4000 were dispersed in deionized water, and zirconium oxychloride octahydrate and urea were added and mixed evenly. The pH of the reaction system was adjusted to 2-4. The resulting mixture was transferred to an autoclave and reacted at 150-180℃ for 12-24 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the precipitate was dried and calcined at 450-550℃ for 1-2 hours.

[0026] Preferably, the mass ratio of cerium oxide / yttrium oxide powder, polyethylene glycol 4000, zirconium oxychloride octahydrate, and urea is (0.1-0.5):(0.001-0.005):(0.05-0.25):(0.5-2.0).

[0027] Preferably, the coating process of the silicon oxide layer includes the following steps:

[0028] Cerium oxide / yttrium oxide / zirconia powder was dispersed in a mixture of ethanol and ammonia, and tetraethyl orthosilicate was slowly added. The mixture was hydrolyzed at room temperature for 5-6 hours. After centrifugation, the precipitate was washed, dried, and calcined at 550°C for 2-3 hours to obtain the carrier.

[0029] Preferably, the concentration of ammonia is 28-30 wt%, the volume ratio of tetraethyl orthosilicate to ammonia is 1:(13-15), the mass ratio of cerium oxide / yttrium oxide / zirconia powder to tetraethyl orthosilicate is 1:(0.4-0.5), and the dropping rate of tetraethyl orthosilicate is 0.5 ml / min.

[0030] Preferably, the concentration of hydrogen peroxide is 4-5 v / v%, the pretreatment temperature is 80°C, and the pretreatment time is 1-2 h; the amount of citric acid added is 10-12 wt% of the pretreatment carrier mass, the heating reaction temperature is 70°C, and the time is 3-4 h.

[0031] Preferably, the process of loading cobalt tetroxide onto the support includes the following steps:

[0032] The hydroxylated carrier was impregnated in a cobalt salt solution, followed by freeze-drying and calcination.

[0033] Preferably, the cobalt salt solution is a cobalt nitrate solution with a concentration of 0.4-0.5 mol / L, the immersion treatment temperature is room temperature, the immersion treatment time is 2-3 hours, and the solid-liquid ratio during the immersion treatment is 1 g: 1 ml.

[0034] Preferably, the freeze-drying process is as follows: first, pre-cool at -50℃ for 1 hour, then dry at -30℃ and vacuum degree of 10Pa for 10-12 hours, and finally dry at room temperature and vacuum degree of 1Pa for 5-6 hours; the calcination process is as follows: first, keep warm at 250℃ for 2 hours, and then raise the temperature to 400℃ and keep warm for 4 hours.

[0035] Preferably, the process of loading palladium onto a support includes the following steps:

[0036] The support loaded with cobalt tetroxide was added to a mixed solution of tetrachloropalladium acid and citric acid for impregnation treatment, followed by stirring and adsorption. After centrifugation, the precipitate was washed, dried, and finally reduced to obtain the catalytic oxidation catalyst.

[0037] Preferably, the molar ratio of tetrachloropalladium acid to citric acid in the mixed solution is 1:2, the concentration of tetrachloropalladium acid is 10-15wt%, the immersion treatment temperature is room temperature, the time is 20-30min, the solid-liquid ratio is 1g:(4-6)ml, the stirring speed for stirring adsorption is 200-300rpm, the temperature is 50℃, and the time is 1-2h.

[0038] Preferably, the reduction process is as follows: in a mixture of hydrogen and nitrogen, reduction is carried out at 500°C for 2 hours, with a volume ratio of hydrogen to nitrogen of 5:95.

[0039] This invention also discloses the application of the catalyst in the treatment of chlorine-containing volatile organic compounds, including the following steps:

[0040] The catalyst was filled into a fixed-bed reactor, and a reaction gas consisting of dichloromethane, nitrogen, and oxygen was introduced into the fixed-bed reactor to carry out a catalytic oxidation reaction.

[0041] In the reaction gases, the concentrations of dichloromethane and oxygen are 1000-3000 ppm and 18-22 vol%, respectively, with nitrogen as the equilibrium gas and a gas hourly space velocity (GHSV) of 15000-20000 ml·g. -1 ·h -1 The catalyst dosage is 0.08-0.15g, and the reaction temperature is 200-400℃.

[0042] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0043] This invention provides a catalyst for treating chlorinated volatile organic compounds (VOCs). The catalyst is a supported catalyst, with the support being a cerium oxide / yttrium oxide / zirconia / silica material with a core-shell structure. The active components include cobalt tetroxide and palladium. The core-shell support of this invention provides a physical barrier and chemical dechlorination, thereby improving the catalyst's resistance to chlorine. Furthermore, the active components composed of Co3O4 and Pd enable low-temperature and high-efficiency oxidation, reducing energy consumption and increasing the removal rate of chlorinated VOCs.

[0044] The catalyst support of this invention uses cerium oxide as its core, with its surface sequentially coated with yttrium oxide, zirconium oxide, and silicon oxide. The cerium oxide core has high stability and controllable oxygen vacancies, which preferentially adsorb chloride ions and convert them into gaseous Cl2 for release, thus preventing chlorine poisoning of the catalyst. The yttrium oxide layer, as the first coating, has an alkaline surface that can neutralize acidic HCl, reducing corrosion to the core, while also stabilizing the cerium oxide lattice and suppressing high-temperature phase transitions. The zirconium oxide layer, as the second coating, has high strength and acidic sites, effectively adsorbing chlorine-containing volatile organic compounds. The silicon oxide layer, as the third coating, blocks the penetration of water vapor and chloride ions, protecting the internal metal active sites.

[0045] The active components of the catalyst of this invention include cobalt tetroxide (Co3O4) and palladium. Co3O4 can activate CH bonds through redox reactions at high temperatures, promoting the dechlorination and ring-opening reactions of chlorinated volatile organic compounds. Furthermore, the strong interaction between cobalt ions and the cerium oxide support can form interfacial oxygen vacancies, accelerating the migration of chloride ions to these vacancies, preventing Co ions from being poisoned by chlorides, and improving the catalyst's stability. A Pd-CoO2 interface can be formed between palladium and Co3O4. x At the active site, Pd is responsible for breaking the C-Cl bond, while Co3O4 dominates the oxidation of the C-C bond. The two work together to remove chlorine-containing volatile organic compounds.

[0046] In preparing the catalyst, the present invention first treats the support with hydrogen peroxide to introduce active groups on the surface of the support, and then modifies it with citric acid to increase the metal loading sites on the surface of the support, thereby ensuring uniform loading of active components and improving the catalytic activity and stability of the catalyst. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0048] Figure 1 The removal rate curves of chlorine-containing volatile organic compounds at different temperatures are shown.

[0049] Figure 2 The catalytic activity of the catalyst within 30 hours. Detailed Implementation

[0050] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0051] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0052] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0053] Example 1

[0054] A method for preparing a catalyst for treating chlorine-containing volatile organic compounds includes the following steps:

[0055] S1. Preparation of core-shell structured carrier:

[0056] S1-1, Preparation of cerium oxide cores:

[0057] Prepare 50 ml of 30 wt% cerium nitrate hexahydrate solution, add urea and trisodium citrate, and control the molar ratio of cerium ions, urea and trisodium citrate to be 1:4:0.15. Stir until the solid dissolves, then heat to 80°C and stir at 600 rpm for 1 h to obtain a sol.

[0058] The sol was transferred to an autoclave and heated to 120°C for 1 hour. The temperature was then increased to 178°C for 20 hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was centrifuged at 8000 rpm for 30 minutes. The precipitate was washed, dried, and the solid obtained was placed in a muffle furnace. Under an air atmosphere, the temperature was first increased to 550°C at a rate of 2°C / min and held for 1.5 hours. Then, the temperature was increased to 950°C at a rate of 5°C / min and held for 4.5 hours. After calcination, the mixture was cooled to 50°C at a rate of 50°C / min under a nitrogen atmosphere and then cooled to room temperature with the furnace to obtain cerium oxide cores.

[0059] S1-2: A yttrium oxide layer is coated on the surface of the cerium oxide core.

[0060] Dissolve 0.9 g of yttrium acetylacetonate in 50 ml of anhydrous ethanol, then add 10% of the molar amount of yttrium acetylacetonate in acetylacetonate, followed by the addition of 0.05 g of deionized water at a rate of 0.1 ml / min. After the addition is complete, hydrolyze at room temperature for 20 min to obtain a transparent sol.

[0061] A transparent sol was added to anhydrous ethanol containing cerium oxide, and the mass ratio of yttrium acetylacetonate to cerium oxide was controlled at 0.9:10. The mixture was heated to 70°C and refluxed for 3 hours under a nitrogen atmosphere. The resulting gel was aged at room temperature for 12 hours and then centrifuged at 6000 rpm for 30 minutes. After centrifugation and drying, the precipitate was placed in a muffle furnace and heated to 300°C at a rate of 1°C / min under an air atmosphere and held for 1 hour. Then, the temperature was increased to 600°C at a rate of 2°C / min and held for 2 hours. Finally, the mixture was cooled to room temperature with the furnace to obtain cerium oxide / yttrium oxide powder.

[0062] S1-3. Coating the surface of the yttrium oxide layer with a zirconium oxide layer:

[0063] 0.1g of cerium oxide / yttrium oxide powder and 0.001g of polyethylene glycol 4000 were dispersed in 80ml of deionized water. 0.05g of zirconium oxychloride octahydrate and 1g of urea were added and mixed evenly. The pH of the reaction system was adjusted to 4. The resulting mixture was transferred to an autoclave and reacted at 160℃ for 24h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the precipitate was dried and calcined at 480℃ for 2h to obtain cerium oxide / yttrium oxide / zirconia powder.

[0064] S1-4. Coat the surface of the zirconium oxide layer with a silicon oxide layer:

[0065] Cerium oxide / yttrium oxide / zirconia powder was dispersed in a mixture of ethanol and 28 wt% ammonia solution. Tetraethyl orthosilicate was added at a rate of 0.5 ml / min, with the volume ratio of tetraethyl orthosilicate to ammonia controlled at 1:13 and the mass ratio of cerium oxide / yttrium oxide / zirconia powder to tetraethyl orthosilicate at 1:0.4. The hydrolysis reaction was carried out at room temperature for 5 h, followed by centrifugation. The precipitate was washed, dried, and calcined at 550 °C for 2 h to obtain the carrier.

[0066] S2, Multimetallic phase active component loading:

[0067] S2-1, Preparation of hydroxylated support:

[0068] 1g of carrier was placed in 50ml of hydrogen peroxide with a concentration of 4v / v%, and treated at 80℃ for 1h. After treatment, it was cooled to room temperature and filtered. The precipitate was dried to obtain the pretreated carrier.

[0069] S2-2. Add the above pretreated carrier to 80 ml of 60 wt% ethanol solution, add citric acid (the amount added is 10 wt% of the mass of the pretreated carrier), heat to 70 °C and react for 3 h. After the reaction is completed, cool to room temperature, filter the reaction solution, and dry the precipitate after filtration to obtain the hydroxylated carrier.

[0070] S2-3, Cobalt tetroxide loaded on a hydroxylation support:

[0071] The hydroxylated support was added to a 0.4 mol / L cobalt nitrate solution, with a solid-liquid ratio of 1 g: 1 ml. The solution was impregnated at room temperature for 2 h. The solid was then removed and subjected to the following steps: first, pre-cooling at -50 °C for 1 h; then drying at -30 °C under a vacuum of 10 Pa for 10 h; and finally drying at room temperature under a vacuum of 1 Pa for 5 h. Finally, the solid was heated in a muffle furnace under an air atmosphere at 250 °C for 2 h, and then heated to 400 °C and held for 4 h to obtain a support loaded with cobalt tetroxide.

[0072] S2-4. Loading palladium metal onto a support:

[0073] Tetrachloropalladium acid and citric acid were added to 50 ml of deionized water at a molar ratio of 1:2 to obtain a mixed solution with a tetrachloropalladium acid concentration of 10 wt%. A support for cobalt tetroxide was added to the mixed solution, and the solid-liquid ratio was controlled at 1 g: 4 ml. The mixture was impregnated at room temperature for 20 min, then heated to 50 °C and stirred at 200 rpm for 1 h for adsorption. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was centrifuged at 6000 rpm for 30 min. The precipitate was washed and dried. The dried solid was placed in a mixture of hydrogen and nitrogen (volume ratio of hydrogen to nitrogen was 5:95) and reduced at 500 °C for 2 h to obtain the catalyst.

[0074] Example 2

[0075] A method for preparing a catalyst for treating chlorine-containing volatile organic compounds includes the following steps:

[0076] S1. Preparation of core-shell structured carrier:

[0077] S1-1, Preparation of cerium oxide cores:

[0078] Prepare 50 ml of 33 wt% cerium nitrate hexahydrate solution, add urea and trisodium citrate, and control the molar ratio of cerium ions, urea and trisodium citrate to be 1:4:0.2. Stir until the solid dissolves, then heat to 80°C and stir at 600 rpm for 2 h to obtain a sol.

[0079] The sol was transferred to an autoclave and heated to 120°C for 1 hour. The temperature was then increased to 180°C for 20 hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was centrifuged at 8000 rpm for 30 minutes. The precipitate was washed, dried, and the solid obtained was placed in a muffle furnace. Under an air atmosphere, the temperature was first increased to 550°C at a rate of 2°C / min and held for 2 hours. Then, the temperature was increased to 950°C at a rate of 5°C / min and held for 4.5 hours. After calcination, the mixture was cooled to 50°C at a rate of 50°C / min under a nitrogen atmosphere and then cooled to room temperature with the furnace to obtain cerium oxide cores.

[0080] S1-2: A yttrium oxide layer is coated on the surface of the cerium oxide core.

[0081] Dissolve 0.95g of yttrium acetylacetone in 50ml of anhydrous ethanol, then add 12% yttrium acetylacetone in acetylacetone, followed by adding 0.07g of deionized water dropwise at a rate of 0.1ml / min. After the addition is complete, hydrolyze at room temperature for 15min to obtain a transparent sol.

[0082] A transparent sol was added to anhydrous ethanol containing cerium oxide, and the mass ratio of yttrium acetylacetonate to cerium oxide was controlled at 1:10. The mixture was heated to 70°C and refluxed for 3.5 h under a nitrogen atmosphere. The resulting gel was aged at room temperature for 12 h and then centrifuged at 6000 rpm for 30 min. After centrifugation and drying, the precipitate was placed in a muffle furnace and heated to 300°C at a rate of 1°C / min under an air atmosphere and held for 1 h. Then, the temperature was increased to 600°C at a rate of 2°C / min and held for 2 h. Finally, the mixture was cooled to room temperature with the furnace to obtain cerium oxide / yttrium oxide powder.

[0083] S1-3. Coating the surface of the yttrium oxide layer with a zirconium oxide layer:

[0084] 0.3g of cerium oxide / yttrium oxide powder and 0.002g of polyethylene glycol 4000 were dispersed in 80ml of deionized water. 0.1g of zirconium oxychloride octahydrate and 1g of urea were added and mixed evenly. The pH of the reaction system was adjusted to 4. The resulting mixture was transferred to an autoclave and reacted at 170℃ for 24h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the precipitate was dried and calcined at 500℃ for 1.5h to obtain cerium oxide / yttrium oxide / zirconia powder.

[0085] S1-4. Coat the surface of the zirconium oxide layer with a silicon oxide layer:

[0086] Cerium oxide / yttrium oxide / zirconia powder was dispersed in a mixture of ethanol and 30 wt% ammonia solution. Tetraethyl orthosilicate was added at a rate of 0.5 ml / min, with the volume ratio of tetraethyl orthosilicate to ammonia controlled at 1:14 and the mass ratio of cerium oxide / yttrium oxide / zirconia powder to tetraethyl orthosilicate at 1:0.45. The hydrolysis reaction was carried out at room temperature for 6 h. After centrifugation, the precipitate was washed, dried, and calcined at 550 °C for 3 h to obtain the carrier.

[0087] S2, Multimetallic phase active component loading:

[0088] S2-1, Preparation of hydroxylated support:

[0089] 1g of carrier was placed in 50ml of hydrogen peroxide with a concentration of 4.5v / v%, and treated at 80℃ for 2h. After treatment, it was cooled to room temperature and filtered. The precipitate was dried to obtain the pretreated carrier.

[0090] S2-2. Add the above pretreated carrier to 80 ml of 60 wt% ethanol solution, add citric acid (11 wt% of the mass of the pretreated carrier), heat to 70 °C and react for 3.5 h. After the reaction is completed, cool to room temperature, filter the reaction solution, and dry the precipitate to obtain the hydroxylated carrier.

[0091] S2-3, Cobalt tetroxide loaded on a hydroxylation support:

[0092] The hydroxylated support was added to a 0.45 mol / L cobalt nitrate solution, with a solid-liquid ratio of 1 g: 1 ml. The solution was impregnated at room temperature for 2 h. The solid was then removed and subjected to the following steps: first, pre-cooling at -50 °C for 1 h; then drying at -30 °C under a vacuum of 10 Pa for 11 h; and finally drying at room temperature under a vacuum of 1 Pa for 5 h. Finally, the solid was heated in a muffle furnace under an air atmosphere at 250 °C for 2 h, and then heated to 400 °C and held for 4 h to obtain a support loaded with cobalt tetroxide.

[0093] S2-4. Loading palladium metal onto a support:

[0094] Tetrachloropalladium acid and citric acid were added to 50 ml of deionized water at a molar ratio of 1:2 to obtain a mixed solution with a tetrachloropalladium acid concentration of 12 wt%. A support for cobalt tetroxide was added to the mixed solution, and the solid-liquid ratio was controlled at 1 g: 5 ml. The mixture was impregnated at room temperature for 25 min, then heated to 50 °C and stirred at 300 rpm for 1.5 h for adsorption. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was centrifuged at 6000 rpm for 30 min. The precipitate was washed and dried. The dried solid was placed in a mixture of hydrogen and nitrogen (volume ratio of hydrogen to nitrogen was 5:95) and reduced at 500 °C for 2 h to obtain the catalyst.

[0095] Example 3

[0096] A method for preparing a catalyst for treating chlorine-containing volatile organic compounds includes the following steps:

[0097] S1. Preparation of core-shell structured carrier:

[0098] S1-1, Preparation of cerium oxide cores:

[0099] Prepare 50 ml of 35 wt% cerium nitrate hexahydrate solution, add urea and trisodium citrate, and control the molar ratio of cerium ions, urea and trisodium citrate to 1:4:0.25. Stir until the solid dissolves, then heat to 80°C and stir at 800 rpm for 2 hours to obtain a sol.

[0100] The sol was transferred to an autoclave and heated to 125°C for 1 hour. The temperature was then increased to 180°C for 20 hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was centrifuged at 8000 rpm for 30 minutes. The precipitate was washed, dried, and the solid was placed in a muffle furnace. Under an air atmosphere, the temperature was first increased to 550°C at a rate of 2°C / min and held for 2 hours. Then, the temperature was increased to 950°C at a rate of 5°C / min and held for 5 hours. After calcination, the mixture was cooled to 50°C at a rate of 50°C / min under a nitrogen atmosphere and then cooled to room temperature with the furnace to obtain cerium oxide cores.

[0101] S1-2: A yttrium oxide layer is coated on the surface of the cerium oxide core.

[0102] Dissolve 0.95g of yttrium acetylacetonate in 50ml of anhydrous ethanol, then add 15% yttrium acetylacetonate in acetylacetonate, followed by dropwise addition of 0.08g of deionized water at a rate of 0.1ml / min. After the addition is complete, hydrolyze at room temperature for 20min to obtain a transparent sol.

[0103] A transparent sol was added to anhydrous ethanol containing cerium oxide, and the mass ratio of yttrium acetylacetonate to cerium oxide was controlled at 1:10. The mixture was heated to 70°C and refluxed for 4 hours under a nitrogen atmosphere. The resulting gel was aged at room temperature for 12 hours and then centrifuged at 6000 rpm for 30 minutes. After centrifugation and drying, the precipitate was placed in a muffle furnace and heated to 300°C at a rate of 1°C / min under an air atmosphere and held for 1 hour. Then, the temperature was increased to 600°C at a rate of 2°C / min and held for 2 hours. Finally, the mixture was cooled to room temperature with the furnace to obtain cerium oxide / yttrium oxide powder.

[0104] S1-3. Coating the surface of the yttrium oxide layer with a zirconium oxide layer:

[0105] 0.5g of cerium oxide / yttrium oxide powder and 0.005g of polyethylene glycol 4000 were dispersed in 80ml of deionized water. 0.25g of zirconium oxychloride octahydrate and 2.0g of urea were added and mixed evenly. The pH of the reaction system was adjusted to 4. The resulting mixture was transferred to an autoclave and reacted at 180℃ for 24h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the precipitate was dried and calcined at 550℃ for 2h to obtain cerium oxide / yttrium oxide / zirconia powder.

[0106] S1-4. Coat the surface of the zirconium oxide layer with a silicon oxide layer:

[0107] Cerium oxide / yttrium oxide / zirconia powder was dispersed in a mixture of ethanol and 30 wt% ammonia solution. Tetraethyl orthosilicate was added at a rate of 0.5 ml / min, with the volume ratio of tetraethyl orthosilicate to ammonia controlled at 1:15 and the mass ratio of cerium oxide / yttrium oxide / zirconia powder to tetraethyl orthosilicate at 1:0.5. The hydrolysis reaction was carried out at room temperature for 6 h, followed by centrifugation. The precipitate was washed, dried, and calcined at 550 °C for 3 h to obtain the carrier.

[0108] S2, Multimetallic phase active component loading:

[0109] S2-1, Preparation of hydroxylated support:

[0110] 1g of carrier was placed in 50ml of 5v / v% hydrogen peroxide and treated at 80℃ for 2h. After treatment, the carrier was cooled to room temperature and filtered. The precipitate was dried to obtain the pretreated carrier.

[0111] S2-2. Add the above pretreated carrier to 80 ml of 60 wt% ethanol solution, add citric acid (the amount added is 12 wt% of the mass of the pretreated carrier), heat to 70 °C and react for 4 h. After the reaction is completed, cool to room temperature, filter the reaction solution, and dry the precipitate after filtration to obtain the hydroxylated carrier.

[0112] S2-3, Cobalt tetroxide loaded on a hydroxylation support:

[0113] The hydroxylated support was added to a 0.5 mol / L cobalt nitrate solution, with a solid-liquid ratio of 1 g: 1 ml. The solution was impregnated at room temperature for 3 h. The solid was then removed and subjected to the following steps: first, pre-cooling at -50 °C for 1 h; then drying at -30 °C under a vacuum of 10 Pa for 12 h; and finally drying at room temperature under a vacuum of 1 Pa for 6 h. Finally, the solid was heated in a muffle furnace under an air atmosphere at 250 °C for 2 h, and then heated to 400 °C and held for 4 h to obtain a support loaded with cobalt tetroxide.

[0114] S2-4. Loading palladium metal onto a support:

[0115] Tetrachloropalladium acid and citric acid were added to 50 ml of deionized water at a molar ratio of 1:2 to obtain a mixed solution with a tetrachloropalladium acid concentration of 15 wt%. A support for cobalt tetroxide was added to the mixed solution, and the solid-liquid ratio was controlled at 1 g: 6 ml. The mixture was impregnated at room temperature for 30 min, then heated to 50 °C and stirred at 300 rpm for 2 h for adsorption. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was centrifuged at 6000 rpm for 30 min. The precipitate was washed and dried. The dried solid was placed in a mixture of hydrogen and nitrogen (volume ratio of hydrogen to nitrogen was 5:95) and reduced at 500 °C for 2 h to obtain the catalyst.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 3 is that S1-2 is not included in this comparative example, but the other operations are the same as in Example 3.

[0118] Comparative Example 2

[0119] The difference between this comparative example and Example 3 is that S1-3 is not included in this comparative example, but the other operations are the same as in Example 3.

[0120] Comparative Example 3

[0121] The difference between this comparative example and Example 3 is that S1-4 are not included in this comparative example, but the other operations are the same as in Example 3.

[0122] Comparative Example 4

[0123] The difference between this comparative example and Example 3 is that S2-1 is not included in this comparative example, but the other operations are the same as in Example 3.

[0124] Comparative Example 5

[0125] The difference between this comparative example and Example 3 is that S2-2 is not included in this comparative example, but the other operations are the same as in Example 3.

[0126] Comparative Example 6

[0127] The difference between this comparative example and Example 3 is that S2-3 is not included in this comparative example, but the other operations are the same as in Example 3.

[0128] Comparative Example 7

[0129] The difference between this comparative example and Example 3 is that S2-4 is not included in this comparative example, but the other operations are the same as in Example 3.

[0130] Test 1:

[0131] The specific surface area and pore size of the catalysts in the above examples and comparative examples were determined using a surface area analyzer (BET), and the results are shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] As can be seen from the test results in Table 1, compared with the examples, Comparative Examples 1-3 lacked Y2O3, ZrO2, or SiO2 layers, resulting in defects in the support and a decrease in specific surface area. Comparative Example 3, in particular, lacked a high specific surface area SiO2 layer, significantly reducing the specific surface area of ​​the catalyst. Comparative Examples 4-5 lacked a surface treatment step, resulting in a slight decrease in specific surface area. Comparative Examples 6 and 7 lacked Co3O4 or palladium loading; due to reduced metal oxide blockage, the specific surface area of ​​the catalyst increased slightly.

[0136] Application Example 1

[0137] The application of catalysts in the treatment of chlorine-containing volatile organic compounds includes the following steps:

[0138] 1. 0.08g of the catalyst from Example 1 was loaded into a quartz tube with a diameter of 6mm, and then fixed with quartz wool to assemble a fixed-bed reactor.

[0139] 2. A reaction gas consisting of dichloromethane, nitrogen, and oxygen is introduced into the fixed-bed reactor described above. The concentrations of dichloromethane and oxygen in the reaction gas are 1000 ppm and 18 vol%, respectively. Nitrogen is used as the equilibrium gas, and the gas hourly space velocity (GHSV) is 15000 ml·g. -1 ·h -1 The reaction temperature is 260℃.

[0140] Application Example 2

[0141] The difference between this application example and application example 1 is that the catalyst of example 2 is used to replace the catalyst of example 1 in an equal amount, while other operations are the same as in application example 1.

[0142] Application Example 3

[0143] The difference between this application example and application example 1 is that the catalyst of example 3 is used to replace the catalyst of example 1 in an equal amount, while other operations are the same as in application example 1.

[0144] Application Comparative Example 1

[0145] The difference between this comparative example and application example 1 is that the catalyst of comparative example 1 is used to replace the catalyst of example 1 in an equal amount, while other operations are the same as in application example 1.

[0146] Application Comparative Example 2

[0147] The difference between this comparative example and application example 1 is that the catalyst of comparative example 2 is used to replace the catalyst of example 1 in an equal amount, while other operations are the same as in application example 1.

[0148] Application Comparative Example 3

[0149] The difference between this comparative example and application example 1 is that the catalyst of comparative example 3 is used to replace the catalyst of example 1 in an equal amount, while other operations are the same as in application example 1.

[0150] Application Comparative Example 4

[0151] The difference between this comparative example and application example 1 is that the catalyst of comparative example 4 is used to replace the catalyst of example 1 in an equal amount, while other operations are the same as in application example 1.

[0152] Application Comparative Example 5

[0153] The difference between this comparative example and application example 1 is that the catalyst of comparative example 5 is used to replace the catalyst of example 1 in an equal amount, while other operations are the same as in application example 1.

[0154] Application Comparative Example 6

[0155] The difference between this comparative example and application example 1 is that the catalyst of comparative example 6 is used to replace the catalyst of example 1 in an equal amount, while other operations are the same as in application example 1.

[0156] Application Comparative Example 7

[0157] The difference between this comparative example and application example 1 is that the catalyst of comparative example 7 is used to replace the catalyst of example 1 in an equal amount, while other operations are the same as in application example 1.

[0158] Test 2:

[0159] The concentration of organic waste gas in the exhaust gas treated by the above method was detected, and the removal rate of chlorine-containing volatile organic compounds was calculated. The results are shown in Table 1.

[0160] The method for calculating the removal rate of chlorine-containing volatile organic compounds is as follows:

[0161] Removal rate (%) = (Content of chlorinated volatile organic compounds at the exhaust gas inlet - Content of chlorinated volatile organic compounds at the exhaust gas outlet) / Content of chlorinated volatile organic compounds at the exhaust gas inlet × 100%.

[0162] Table 1

[0163] Removal rate of chlorine-containing volatile organic compounds, % Application Example 1 94.5 Application Example 2 95.2 Application Example 3 95.8 Application Comparative Example 1 88.1 Application Comparative Example 2 87.3 Application Comparative Example 3 75.0 Application Comparative Example 4 92.1 Application Comparative Example 5 91.5 Application Comparative Example 6 82.3 Application Comparative Example 7 81.9

[0164] As can be seen from the test results in Tables 1 and 2, compared with the comparative example, the catalyst prepared in the embodiments of the present invention has higher catalytic activity when treating chlorine-containing volatile organic compounds, and has a good removal effect at a lower temperature with low energy consumption.

[0165] In the catalyst support of the examples, cerium oxide serves as the core, with a Y₂O₃ layer, a ZrO₂ layer, and a silicon oxide layer sequentially coated on its surface. The Y₂O₃ layer stabilizes CeO₂ and provides oxygen vacancies; the ZrO₂ layer provides acidic sites; and the SiO₂ layer provides a high specific surface area for the catalyst and protects the core, thereby effectively improving the catalyst's activity. In Comparative Examples 1-3, the absence of either the Y₂O₃ layer, the ZrO₂ layer, or the SiO₂ layer resulted in a decrease in the removal rate of chlorine-containing volatile organic compounds.

[0166] To better achieve the loading of active components, this invention pretreats the support. First, hydrogen peroxide is used to treat the support, introducing active groups such as hydroxyl groups onto the support surface. Then, citric acid is used for treatment, facilitating the subsequent orderly anchoring of the active components to the active sites on the support through chelation. Comparative Example 4 did not use hydrogen peroxide treatment, and Comparative Example 5 did not use citric acid treatment. In these cases, the loading of active components on the support was uneven, resulting in a reduced specific surface area of ​​the catalyst and affecting its catalytic activity.

[0167] The active components of the catalyst of this invention include cobalt tetroxide and palladium. Palladium preferentially adsorbs and breaks C-Cl bonds to generate Cl-, which rapidly migrates to the Co3O4 surface and is oxidized and removed, preventing palladium from being deactivated by chlorine coverage and improving catalyst activity. The catalyst in Comparative Example 6 lacks cobalt tetroxide, and the catalyst in Comparative Example 7 lacks palladium; both catalysts exhibit significantly reduced catalytic activity.

[0168] Test 3:

[0169] To verify the catalytic activity of the catalyst of the present invention, chlorine-containing volatile organic compounds were treated according to the method of Application Example 1 at treatment temperatures of 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 320℃, 340℃, 360℃, 380℃, and 400℃. The removal rates of chlorine-containing volatile organic compounds at different temperatures were plotted as curves. Figure 1 As shown.

[0170] from Figure 1 It can be seen that when the reaction temperature is 200℃, the removal rate of chlorine-containing volatile organic compounds reaches more than 30%, while when the reaction temperature is 240℃, the removal rate of chlorine-containing volatile organic compounds reaches more than 60%, and when the reaction temperature is 280℃, the removal rate of chlorine-containing volatile organic compounds reaches more than 98%, proving that the catalyst of the present invention has high catalytic activity.

[0171] Test 4:

[0172] To verify the stability of the catalyst, its catalytic activity was tested at 400℃ for 30 hours. The test results are as follows: Figure 2 As shown. From Figure 2 It can be seen that during the 30-hour test period, the catalyst of Example 1 has high catalytic activity, and the removal rate of chlorine-containing volatile organic compounds is basically maintained at 100%, showing good stability, that is, good chlorine resistance.

[0173] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing a catalyst for treating chlorine-containing volatile organic compounds, characterized in that, Includes the following steps: (1) Preparation of core-shell structured carrier: A 30-35 wt% solution of cerium nitrate hexahydrate is mixed with urea and trisodium citrate, and the molar ratio of cerium ions, urea and trisodium citrate is controlled at 1:4:(0.15-0.25). The mixture is heated to 80°C at a speed of 600-800 rpm and stirred for 1-2 hours to obtain a sol. The above sol was transferred to an autoclave and heated to 115-125℃ for 1 hour. Then the temperature was increased to 175-180℃ for 20-22 hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was centrifuged, and the precipitate was washed, dried, and placed in a muffle furnace. Under an air atmosphere, the temperature was first increased to 550℃ at a rate of 2℃ / min and held for 1.5-2 hours. Then the temperature was increased to 950℃ at a rate of 5℃ / min and held for 4.5-5 hours. After calcination, the mixture was cooled to 50℃ at a rate of 50℃ / min under a nitrogen atmosphere, and then cooled to room temperature with the furnace to obtain cerium oxide cores. A yttrium oxide layer, a zirconium oxide layer, and a silicon oxide layer are sequentially coated onto the surface of a cerium oxide core to obtain a carrier; (2) Multimetal phase active component loading: The carrier is treated with hydrogen peroxide to obtain a pretreated carrier; the concentration of the hydrogen peroxide is 4-5 v / v%, the pretreatment temperature is 80℃, and the pretreatment time is 1-2 h. The pretreated carrier was added to an ethanol solution, citric acid was added, and the reaction was carried out at a high temperature to obtain a hydroxylated carrier. The amount of citric acid added was 10-12 wt% of the mass of the pretreated carrier, and the temperature of the reaction was 70°C for 3-4 hours. Cobalt tetroxide and palladium metal were sequentially loaded onto a hydroxylation support to obtain a catalyst.

2. The method for preparing a catalyst for treating chlorine-containing volatile organic compounds according to claim 1, characterized in that, The yttrium oxide coating process includes the following steps: Yttrium acetylacetonate was dissolved in anhydrous ethanol, then acetylacetonate was added, followed by deionized water at a rate of 0.1 ml / min. The mass ratio of yttrium acetylacetonate to deionized water was controlled at (0.9-1):(0.05-0.08), and the amount of acetylacetonate added was controlled at 10-15% of the molar amount of yttrium acetylacetonate. Hydrolysis was carried out at room temperature for 10-20 min to obtain a transparent sol. A transparent sol was added to anhydrous ethanol containing cerium oxide, and the mass ratio of yttrium acetylacetone to cerium oxide was controlled at (0.9-1):

10. The mixture was heated to 70°C and refluxed for 3-4 hours under a nitrogen atmosphere. The resulting gel was aged at room temperature for 12 hours and then centrifuged. After centrifugation and drying, the precipitate was placed in a muffle furnace and heated to 300°C at a rate of 1°C / min under an air atmosphere and held for 1 hour. Then, the temperature was increased to 600°C at a rate of 2°C / min and held for 2 hours. Finally, the mixture was cooled to room temperature with the furnace to obtain cerium oxide / yttrium oxide powder.

3. The method for preparing a catalyst for treating chlorine-containing volatile organic compounds according to claim 1, characterized in that, The process of coating a zirconia layer includes the following steps: Cerium oxide / yttrium oxide powder and polyethylene glycol 4000 were dispersed in deionized water. Zirconium oxychloride octahydrate and urea were added and mixed evenly. The mass ratio of cerium oxide / yttrium oxide powder, polyethylene glycol 4000, zirconium oxychloride octahydrate and urea was controlled to be (0.1-0.5):(0.001-0.005):(0.05-0.25):(0.5-2.0). The pH of the reaction system was adjusted to 2-4. The resulting mixture was transferred to an autoclave and reacted at 150-180℃ for 12-24 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the precipitate was dried and calcined at 450-550℃ for 1-2 hours.

4. The method for preparing a catalyst for treating chlorine-containing volatile organic compounds according to claim 1, characterized in that, The process of coating a silicon oxide layer includes the following steps: Cerium oxide / yttrium oxide / zirconia powder was dispersed in a mixture of ethanol and 28-30 wt% ammonia. Tetraethyl orthosilicate was added at a rate of 0.5 ml / min, with the volume ratio of tetraethyl orthosilicate to ammonia controlled at 1:(13-15) and the mass ratio of cerium oxide / yttrium oxide / zirconia powder to tetraethyl orthosilicate controlled at 1:(0.4-0.5). The hydrolysis reaction was carried out at room temperature for 5-6 h, followed by centrifugation. The precipitate was washed, dried, and calcined at 550 °C for 2-3 h to obtain the carrier.

5. The method for preparing a catalyst for treating chlorine-containing volatile organic compounds according to claim 1, characterized in that, The process of loading cobalt tetroxide onto a carrier includes the following steps: The hydroxylated support was added to a cobalt nitrate solution with a concentration of 0.4-0.5 mol / L, and the solid-liquid ratio was controlled at 1 g: 1 ml. The solution was impregnated at room temperature for 2-3 h. After impregnation, the solid was taken out and pre-cooled at -50℃ for 1 h, then dried at -30℃ and a vacuum of 10 Pa for 10-12 h, and finally dried at room temperature and a vacuum of 1 Pa for 5-6 h. The dried solid was kept at 250℃ in air for 2 h, and then heated to 400℃ and kept at 4 h to obtain a support loaded with cobalt tetroxide.

6. The method for preparing a catalyst for treating chlorine-containing volatile organic compounds according to claim 1, characterized in that, The process of loading palladium onto a support includes the following steps: The support loaded with cobalt tetroxide was added to a mixed solution of tetrachloropalladium acid and citric acid, with a molar ratio of tetrachloropalladium acid to citric acid of 1:2 and a concentration of tetrachloropalladium acid of 10-15 wt%. The solid-liquid ratio was controlled at 1 g: (4-6) ml. The mixture was impregnated at room temperature for 20-30 min, then heated to 50 °C and stirred at 200-300 rpm for 1-2 h for adsorption. After centrifugation, the precipitate was washed and dried. The dried solid was then reduced at 500 °C for 2 h under a mixed gas of hydrogen and nitrogen, with a volume ratio of hydrogen to nitrogen of 5:95, to obtain the catalyst.

7. The application of the catalyst prepared according to any one of claims 1 to 6 in the treatment of chlorine-containing volatile organic compounds, characterized in that, Includes the following steps: The catalyst is packed into a fixed-bed reactor, and a reaction gas consisting of dichloromethane, nitrogen, and oxygen is introduced into the fixed-bed reactor to carry out the catalytic oxidation reaction.

8. The application of the catalyst according to claim 7 in the treatment of chlorine-containing volatile organic compounds, characterized in that, The concentrations of dichloromethane and oxygen in the reaction gases are 1000-3000 ppm and 18-22 vol%, respectively, with nitrogen as the equilibrium gas and a gas hourly space velocity (GHSV) of 15000-20000 ml·g. -1 ·h -1 The catalyst dosage is 0.08-0.15g, and the reaction temperature is 200-400℃.

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