Preparation method and application of catalyst for treating chlorine-containing volatile organic compounds

Abstract

The invention 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.The preparation method comprises the following steps that a core-shell structure carrier is prepared, sequentially coating the surface of the cerium oxide core with an yttrium oxide layer, a zirconium oxide layer and a silicon oxide layer to obtain a carrier; multi-metal-phase active component loading: placing the carrier in hydrogen peroxide for treatment to obtain a pretreated carrier; adding the pretreated carrier into an ethanol solution, adding citric acid, and heating for reaction to obtain a hydroxylated carrier; and sequentially loading cobaltosic oxide and metal palladium on the hydroxylation carrier to obtain the catalyst. The catalyst provided by the invention has high catalytic activity and stability, and can effectively remove chlorine-containing volatile organic compounds.

Description

Technical Field

[0001] The present invention relates to the technical field of organic waste gas treatment, and in particular to a preparation method and application of a catalyst for treating chlorine-containing volatile organic compounds. Background Art

[0002] Chlorinated volatile organic compounds (CVOCs) are often produced in large quantities in the chemical, pharmaceutical, coating, and pesticide synthesis industries. These substances are 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 highly electronegative chlorine element in CVOC molecules easily binds to the active sites of catalysts, causing poisoning and deactivation, further increasing the difficulty of their control.

[0003] At present, the main treatment methods for chlorinated volatile organic compounds include the following: 1. Incineration method: This method is suitable for high-concentration exhaust gas, but it needs to maintain high temperature (>800℃), consumes huge energy, and is easy to generate dioxins and corrosive HCl. It requires supporting alkaline washing towers and anti-corrosion equipment, which is expensive. 2. Adsorption method: Some organic matter can be recovered, but the adsorption capacity is limited, and the treatment effect of low-boiling point chlorinated volatile organic compounds is poor; and the adsorbent is frequently regenerated after saturation, which is easy to cause secondary pollution. 3. Catalytic combustion method: Chlorinated volatile organic compounds are degraded at a lower temperature (200-450℃). This method has low energy consumption and is widely used. However, existing catalysts face the following problems: (1) Poor resistance to chlorine poisoning; (2) Insufficient adaptability to high concentrations: when the exhaust gas concentration is >6000mg / Nm 3 When, the reaction exotherm is intense, causing the catalyst to sinter or the active component to volatilize. To solve the above-mentioned technical problems, conventional catalysts have been improved in the prior art, for example, to improve the chlorine resistance and stability of the catalyst, researchers have introduced the precious metal Ru, Ru element can enhance the C-Cl bond breaking ability, but it is easily converted into volatile RuCl3 and lost under high humidity, and it is necessary to add alkaline earth metals (Ca / Mg) to stabilize the valence state, and the cost increases and high temperature stability is still insufficient; It is also found that when non-precious metals such as Mn and vanadium are introduced, the obtained catalyst cost is relatively low, but the oxygen migration efficiency is limited, and it is easy to deposit carbon when processing high concentrations of chlorinated volatile organic compounds, and the acidic site is weak to the removal ability of Cl, resulting in chlorine accumulation and deactivation. Therefore, for the above-mentioned problems, it is necessary to provide a catalyst having high activity, strong chlorine resistance, high concentration adaptability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: in view of the shortcomings of the existing technology, a preparation method and application of a catalyst for treating chlorinated volatile organic compounds are provided. The catalyst prepared by this method not only has high catalytic activity but also good stability, and can effectively remove chlorinated volatile organic compounds.

[0005] In order to solve the above technical problems, the technical solution of the present invention is:

[0006] A method for preparing a catalyst for treating chlorinated volatile organic compounds comprises the following steps:

[0007] (1) Preparation of core-shell structure carriers:

[0008] preparing cerium oxide cores;

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

[0010] (2) Multi-metal phase active component loading:

[0011] The carrier is placed in hydrogen peroxide for treatment to obtain a pretreated carrier;

[0012] The pretreated carrier is added to an ethanol solution, citric acid is added, and the temperature is raised to react to obtain a hydroxylated carrier;

[0013] Cobaltous oxide and metal palladium are loaded on the hydroxylation carrier in sequence to obtain a catalyst.

[0014] Preferably, the preparation process of the cerium oxide core comprises the following steps:

[0015] Heating and stirring a mixed solution of cerium nitrate hexahydrate solution with a concentration of 30-35 wt%, urea, and trisodium citrate to obtain a sol;

[0016] The sol was transferred into an autoclave, heated to 115-125°C, reacted for 1 hour, then heated to 175-180°C, reacted for 20-22 hours, and cooled to room temperature after the reaction was completed. The reaction solution was centrifuged, the centrifugal precipitate was washed, dried, and then 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° C., the stirring speed is 600-800 rpm, and the stirring time is 1-2 h.

[0018] Preferably, the process for preparing the cerium oxide core by calcining is as follows: in an air atmosphere, first, heating to 550°C at a rate of 2°C / min, keeping warm for 1.5-2h, then heating to 950°C at a rate of 5°C / min, keeping warm for 4.5-5h, and after calcination, cooling to 50°C at a rate of 50°C / min in a nitrogen atmosphere, and then cooling to room temperature with the furnace.

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

[0020] Dissolve yttrium acetylacetonate in anhydrous ethanol, then add acetylacetone, and then slowly add deionized water dropwise for hydrolysis to obtain a transparent sol;

[0021] The transparent sol was added to anhydrous ethanol containing cerium oxide, and the temperature was raised to 70° C. under nitrogen atmosphere and refluxed for 3-4 hours. The resulting gel was aged at room temperature for 12 hours and then centrifuged. The centrifugal 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 acetylacetone added is 10-15% of the molar amount of yttrium acetylacetonate; the deionization addition rate is 0.1 ml / min, and the hydrolysis is carried out at room temperature for 10-20 minutes after the deionized water is added.

[0023] Preferably, the calcination process for preparing cerium oxide / yttrium oxide is: first, heating to 300°C at a rate of 1°C / min, keeping warm for 1 hour, then heating to 600°C at a rate of 2°C / min, keeping warm for 2 hours, and finally cooling to room temperature with the furnace.

[0024] Preferably, the coating process of the zirconium oxide layer comprises the following steps:

[0025] Disperse cerium oxide / yttrium oxide powder and polyethylene glycol 4000 in deionized water, add zirconium oxychloride octahydrate and urea and mix evenly. Adjust the pH of the reaction system to 2-4. Transfer the resulting mixture to an autoclave and react at 150-180°C for 12-24 hours. After the reaction, cool to room temperature, filter, and precipitate and dry, then calcine at 450-550°C 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 comprises the following steps:

[0028] Cerium oxide / yttrium oxide / zirconium oxide powders were dispersed in a mixture of ethanol and ammonia water, and ethyl orthosilicate was slowly added. The mixture was hydrolyzed at room temperature for 5-6 hours, and then centrifuged. The centrifugal precipitate was washed, dried, and calcined at 550°C for 2-3 hours to obtain a carrier.

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

[0030] Preferably, the concentration of the 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 mass of the pretreated carrier, the temperature of the temperature-raising reaction is 70° C., and the time is 3-4 h.

[0031] Preferably, the process of loading cobalt trioxide on a carrier comprises the following steps:

[0032] The hydroxylated support is added to a cobalt salt solution for impregnation treatment, and then freeze-dried and calcined in sequence.

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

[0034] Preferably, the freeze-drying process is: first pre-cooling at -50°C for 1 hour, then drying at -30°C and a vacuum degree of 10Pa for 10-12 hours, and finally drying at room temperature and a vacuum degree of 1Pa for 5-6 hours; the roasting process is: first keeping warm at 250°C for 2 hours, then heating to 400°C and keeping warm for 4 hours.

[0035] Preferably, the process of loading metallic palladium on a carrier comprises the following steps:

[0036] The carrier loaded with cobalt trioxide is added into a mixed solution of tetrachloropalladium acid and citric acid, and is immersed in the solution, then stirred for adsorption, centrifuged, washed, dried, and finally reduced to obtain a catalytic oxidation catalyst.

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

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

[0039] The present invention also discloses the use of a catalyst in treating chlorine-containing volatile organic compounds, comprising the following steps:

[0040] The catalyst is filled in a fixed bed reactor, and a reaction gas consisting of dichloromethane, nitrogen and oxygen is introduced into the fixed bed reactor to perform a catalytic oxidation reaction.

[0041] The concentrations of dichloromethane and oxygen in the reaction gas are 1000-3000ppm and 18-22v%, respectively. Nitrogen is the balance gas, and the gas space velocity is 15000-20000ml·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] The present invention provides a catalyst for treating chlorinated volatile organic compounds. The catalyst is a supported catalyst, wherein the carrier adopts a cerium oxide / yttrium oxide / zirconium oxide / silicon oxide material having a core-shell structure, and the active components include cobalt oxide and metal palladium. The core-shell carrier of the present invention can provide a physical barrier and chemical dechlorination effects, thereby improving the chlorine resistance of the catalyst. In addition, the active components composed of Co3O4 and Pd achieve low-temperature and high-efficiency oxidation, reduce energy consumption, and improve the removal rate of chlorinated volatile organic compounds.

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

[0045] The active components of the catalyst of the present invention include cobalt trioxide and palladium. Co3O4 can activate C-H bonds through redox reaction at high temperature, promoting the dechlorination ring-opening reaction of chlorine-containing volatile organic compounds. In addition, the strong interaction between cobalt ions and cerium oxide carrier can form interfacial oxygen vacancies, accelerate the migration of chloride ions to the carrier oxygen vacancies, prevent Co ions from being poisoned by chloride, and improve the stability of the catalyst. The interface between palladium and Co3O4 can form Pd-CoO x At the active site, Pd is responsible for breaking the C-Cl bond, and Co3O4 leads the CC bond oxidation, and the two work together to achieve the removal of chlorinated volatile organic compounds.

[0046] When preparing the catalyst, the present invention first uses hydrogen peroxide to treat the carrier to introduce active groups on the carrier surface, and then uses citric acid to modify the carrier surface to increase the metal loading sites, thereby ensuring uniform loading of the active components and improving the catalytic activity and stability of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0048] Figure 1 is the removal rate curve of chlorinated volatile organic compounds at different temperatures;

[0049] Figure 2 is the catalytic activity of the catalyst within 30 h. DETAILED DESCRIPTION

[0050] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0051] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0052] In order 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, rather than limiting the claims of the present invention.

[0053] Example 1

[0054] A method for preparing a catalyst for treating chlorinated volatile organic compounds comprises the following steps:

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

[0056] S1-1. Preparation of cerium oxide core:

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

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

[0059] S1-2: Coating the yttrium oxide layer on the surface of the cerium oxide core:

[0060] 0.9 g of yttrium acetylacetonate was dissolved in 50 ml of anhydrous ethanol, and then acetylacetone (10% of the molar amount of yttrium acetylacetonate) was added. Then, 0.05 g of deionized water was added dropwise at a rate of 0.1 ml / min. After the addition was completed, the mixture was hydrolyzed at room temperature for 20 min to obtain a transparent sol.

[0061] The transparent sol was added to anhydrous ethanol of cerium oxide, and the mass ratio of yttrium acetylacetonate to cerium oxide was controlled to be 0.9:10. The temperature was raised to 70°C under a nitrogen atmosphere and refluxed for 3 hours. The resulting gel was aged at room temperature for 12 hours and then centrifuged at 6000 rpm for 30 minutes. The centrifugal precipitate was dried and placed in a muffle furnace. The temperature was first raised to 300°C at a rate of 1°C / min under an air atmosphere, and kept warm for 1 hour. Then, the temperature was raised to 600°C at a rate of 2°C / min, and kept warm for 2 hours. Finally, the cerium oxide / yttrium oxide powder was cooled to room temperature in the furnace.

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

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

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

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

[0066] S2. Multi-metal phase active component loading:

[0067] S2-1. Preparation of hydroxylated carrier:

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

[0069] S2-2, the pretreated carrier was added to 80 ml of 60 wt% ethanol solution, citric acid was added (the amount added was 10 wt% of the mass of the pretreated carrier), the temperature was raised to 70 ° C. and the reaction was carried out for 3 h. After the reaction was completed, the reaction solution was cooled to room temperature, the reaction solution was filtered, and the precipitate was dried to obtain the hydroxylated carrier;

[0070] S2-3, loading cobalt tetroxide on a hydroxylated 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, and the solution was immersed at room temperature for 2 h. The solid was then taken out and pre-cooled at -50°C for 1 h, then dried at -30°C and a vacuum of 10 Pa for 10 h, and finally dried at room temperature and a vacuum of 1 Pa for 5 h. Finally, the solution was kept at 250°C for 2 h in an air atmosphere in a muffle furnace, and then heated to 400°C and kept for 4 h to obtain a support loaded with cobalt tetroxide.

[0072] S2-4. Loading metallic palladium on the carrier:

[0073] Tetrachloropalladium acid and citric acid are added to 50 ml of deionized water in a molar ratio of 1:2 to obtain a mixed solution, wherein the concentration of tetrachloropalladium acid in the mixed solution is 10 wt %. A carrier loaded with cobalt tetroxide is added to the mixed solution, and the solid-liquid ratio is controlled to be 1 g:4 ml. The mixture is immersed at room temperature for 20 minutes, then heated to 50° C., stirred and adsorbed at 200 rpm for 1 hour, and cooled to room temperature after the reaction is completed. The reaction solution is centrifuged at 6000 rpm for 30 minutes, the precipitate is washed, and then dried. The dried solid is placed in a mixture of hydrogen and nitrogen (the volume ratio of hydrogen and nitrogen is 5:95), and reduced at 500° C. for 2 hours to obtain a catalyst.

[0074] Example 2

[0075] A method for preparing a catalyst for treating chlorinated volatile organic compounds comprises the following steps:

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

[0077] S1-1. Preparation of cerium oxide core:

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

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

[0080] S1-2: Coating the yttrium oxide layer on the surface of the cerium oxide core:

[0081] 0.95 g of yttrium acetylacetonate was dissolved in 50 ml of anhydrous ethanol, and then acetylacetone (12% of the molar amount of yttrium acetylacetonate) was added. Then, 0.07 g of deionized water was added dropwise at a rate of 0.1 ml / min. After the addition was completed, the mixture was hydrolyzed at room temperature for 15 min to obtain a transparent sol.

[0082] The transparent sol was added to anhydrous ethanol of cerium oxide, and the mass ratio of yttrium acetylacetonate to cerium oxide was controlled to be 1:10. The temperature was raised to 70°C under a nitrogen atmosphere and refluxed for 3.5 hours. The resulting gel was aged at room temperature for 12 hours and then centrifuged at 6000 rpm for 30 minutes. The centrifugal precipitate was dried and placed in a muffle furnace. The temperature was first raised to 300°C at a rate of 1°C / min under an air atmosphere, and kept warm for 1 hour. Then, the temperature was raised to 600°C at a rate of 2°C / min, and kept warm for 2 hours. Finally, the cerium oxide / yttrium oxide powder was cooled to room temperature in the furnace.

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

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

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

[0086] Cerium oxide / yttrium oxide / zirconium oxide powder was dispersed in a mixture of ethanol and 30 wt% ammonia water, and tetraethyl orthosilicate was added at a rate of 0.5 ml / min. The volume ratio of tetraethyl orthosilicate to ammonia water was controlled to be 1:14, and the mass ratio of cerium oxide / yttrium oxide / zirconium oxide powder to tetraethyl orthosilicate was controlled to be 1:0.45. The mixture was hydrolyzed at room temperature for 6 h, followed by centrifugation. The centrifugal precipitate was washed, dried, and then calcined at 550° C. for 3 h to obtain a carrier.

[0087] S2. Multi-metal phase active component loading:

[0088] S2-1. Preparation of hydroxylated carrier:

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

[0090] S2-2, the pretreated carrier was added to 80 ml of 60 wt% ethanol solution, citric acid was added (the amount added was 11 wt% of the mass of the pretreated carrier), the temperature was raised to 70 ° C. and the reaction was carried out for 3.5 hours. After the reaction was completed, the reaction mixture was cooled to room temperature, the reaction solution was filtered, and the precipitate was dried to obtain the hydroxylated carrier;

[0091] S2-3, loading cobalt tetroxide on a hydroxylated 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, and the solution was immersed at room temperature for 2 h. The solid was then taken out and pre-cooled at -50°C for 1 h, then dried at -30°C and a vacuum of 10 Pa for 11 h, and finally dried at room temperature and a vacuum of 1 Pa for 5 h. Finally, the solution was kept at 250°C for 2 h in an air atmosphere in a muffle furnace, and then heated to 400°C and kept for 4 h to obtain a support loaded with cobalt tetroxide.

[0093] S2-4. Loading metallic palladium on the carrier:

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

[0095] Example 3

[0096] A method for preparing a catalyst for treating chlorinated volatile organic compounds comprises the following steps:

[0097] S1. Preparation of core-shell structure carriers:

[0098] S1-1. Preparation of cerium oxide core:

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

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

[0101] S1-2: Coating the yttrium oxide layer on the surface of the cerium oxide core:

[0102] 0.95 g of yttrium acetylacetonate was dissolved in 50 ml of anhydrous ethanol, and then acetylacetone (15% of the molar amount of yttrium acetylacetonate) was added. Then, 0.08 g of deionized water was added dropwise at a rate of 0.1 ml / min. After the addition was completed, the mixture was hydrolyzed at room temperature for 20 min to obtain a transparent sol.

[0103] The transparent sol was added to anhydrous ethanol of cerium oxide, and the mass ratio of yttrium acetylacetonate to cerium oxide was controlled to be 1:10. The temperature was raised to 70°C under a nitrogen atmosphere and refluxed for 4 hours. The resulting gel was aged at room temperature for 12 hours and then centrifuged at 6000 rpm for 30 minutes. The centrifugal precipitate was dried and placed in a muffle furnace. The temperature was first raised to 300°C at a rate of 1°C / min under an air atmosphere, and kept warm for 1 hour. Then, the temperature was raised to 600°C at a rate of 2°C / min, and kept warm for 2 hours. Finally, the cerium oxide / yttrium oxide powder was cooled to room temperature in the furnace.

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

[0105] 0.5 g of cerium oxide / yttrium oxide powder and 0.005 g of polyethylene glycol 4000 were dispersed in 80 ml of deionized water, 0.25 g of zirconium oxychloride octahydrate and 2.0 g 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°C for 24 h. After the reaction was completed, it was cooled to room temperature and filtered. The precipitate was dried and then calcined at 550°C for 2 h to obtain cerium oxide / yttrium oxide / zirconium oxide powder.

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

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

[0108] S2. Multi-metal phase active component loading:

[0109] S2-1. Preparation of hydroxylated carrier:

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

[0111] S2-2, the pretreated carrier was added to 80 ml of 60 wt% ethanol solution, citric acid was added (the amount added was 12 wt% of the mass of the pretreated carrier), the temperature was raised to 70 ° C. and the reaction was carried out for 4 hours. After the reaction was completed, the reaction mixture was cooled to room temperature, the reaction solution was filtered, and the precipitate was dried to obtain the hydroxylated carrier;

[0112] S2-3, loading cobalt tetroxide on a hydroxylated 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, and the solution was immersed at room temperature for 3 hours. The solid was then taken out and pre-cooled at -50°C for 1 hour, then dried at -30°C and a vacuum of 10 Pa for 12 hours, and finally dried at room temperature and a vacuum of 1 Pa for 6 hours. Finally, the solution was kept at 250°C for 2 hours in an air atmosphere in a muffle furnace, and then heated to 400°C and kept for 4 hours to obtain a support loaded with cobalt tetroxide.

[0114] S2-4. Loading metallic palladium on the carrier:

[0115] Tetrachloropalladium acid and citric acid are added to 50 ml of deionized water in a molar ratio of 1:2 to obtain a mixed solution, wherein the concentration of tetrachloropalladium acid in the mixed solution is 15 wt %. A carrier loaded with cobalt tetroxide is added to the mixed solution, and the solid-liquid ratio is controlled to be 1 g:6 ml. The mixture is immersed at room temperature for 30 minutes, then heated to 50°C, stirred and adsorbed at 300 rpm for 2 hours, and cooled to room temperature after the reaction is completed. The reaction solution is centrifuged at 6000 rpm for 30 minutes, the precipitate is washed, and then dried. The dried solid is placed in a mixture of hydrogen and nitrogen (the volume ratio of hydrogen and nitrogen is 5:95), and reduced at 500°C for 2 hours to obtain a 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, and other operations are the same as those 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, and other operations are the same as those in Example 3.

[0120] Comparative Example 3

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

[0130] Test 1:

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

[0132] Table 1

[0133]

[0134]

[0135] The test results in Table 1 show that, compared to the Examples, Comparative Examples 1-3 lack a Y2O3 layer, a ZrO2 layer, or a SiO2 layer, resulting in support defects and a reduction in specific surface area. In particular, Comparative Example 3 lacks the high-specific-surface-area SiO2 layer, significantly reducing the specific surface area of ​​the catalyst. Comparative Examples 4-5, however, lack a surface treatment step, resulting in a slight reduction in specific surface area. Comparative Examples 6 and 7 lack Co3O4 or palladium loading, resulting in a slight increase in the specific surface area of ​​the catalyst due to reduced metal oxide clogging.

[0136] Application Example 1

[0137] The application of the catalyst in treating chlorinated volatile organic compounds comprises the following steps:

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

[0139] 2. A reaction gas consisting of dichloromethane, nitrogen, and oxygen was introduced into the fixed bed reactor for reaction. The concentrations of dichloromethane and oxygen in the reaction gas were 1000 ppm and 18% by volume, respectively. Nitrogen was used as the balance gas, and the gas space velocity was 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 1 is replaced by the catalyst of example 2 in equal amount, and the other operations are the same as those of 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 in equal amounts to replace the catalyst of example 1, and other operations are the same as those of application example 1.

[0144] Comparative Application Example 1

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

[0150] Comparative Application 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 equal amount, and other operations are the same as those of application example 1.

[0152] Comparative Application Example 5

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

[0158] Test 2:

[0159] The organic waste gas concentration in the waste gas treated by the above method is tested below, and the removal rate of chlorinated volatile organic compounds is calculated. The results are shown in Table 1.

[0160] The calculation method for the removal rate of chlorinated volatile organic compounds is as follows:

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

[0162] Table 1

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

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

[0165] The catalyst supports in the examples use cerium oxide as a core, coated sequentially with a Y2O3 layer, a ZrO2 layer, and a silicon oxide layer. The Y2O3 layer stabilizes the CeO2 and provides oxygen vacancies; the ZrO2 layer provides acidic sites; and the SiO2 layer provides a high surface area for the catalyst, protecting the core and thus effectively improving catalyst activity. Comparative Examples 1-3, which lack either the Y2O3 layer, the ZrO2 layer, or the SiO2 layer, all exhibit reduced removal rates for chlorinated volatile organic compounds.

[0166] To better load the active components, the present invention pre-treats the support. First, the support is treated with hydrogen peroxide to introduce active groups such as hydroxyl groups onto the support surface. Then, the support is treated with citric acid to facilitate the subsequent orderly anchoring of the active components to the active sites of the support through chelation. Comparative Example 4, which did not use hydrogen peroxide treatment, and Comparative Example 5, which did not use citric acid treatment, exhibited uneven loading of the active components on the support, resulting in a reduced specific surface area of ​​the catalyst and a reduction in its catalytic activity.

[0167] The active components of the catalyst of the present invention include cobalt trioxide and palladium. The palladium preferentially adsorbs and cleaves C-Cl bonds to generate Cl-. This Cl- rapidly migrates to the surface of Co3O4 and is oxidized and removed, preventing the palladium from being deactivated by chlorine coating and improving the catalyst's activity. The catalyst of Comparative Example 6 lacks cobalt trioxide, and the catalyst of Comparative Example 7 lacks palladium, resulting in significantly reduced catalytic activity.

[0168] Test three:

[0169] In order to verify the catalytic activity of the catalyst of the present invention, chlorinated volatile organic compounds were treated according to the method of Application Example 1. The treatment temperatures were 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, 340°C, 360°C, 380°C, and 400°C, respectively. The removal rates of chlorinated volatile organic compounds at different temperatures were plotted as curves, as shown in FIG. Figure 1 shown.

[0170] from Figure 1 It can be seen that when the reaction temperature is 200°C, the removal rate of chlorinated volatile organic compounds reaches more than 30%, when the reaction temperature is 240°C, the removal rate of chlorinated volatile organic compounds reaches more than 60%, and when the reaction temperature is 280°C, the removal rate of chlorinated volatile organic compounds reaches more than 98%, which proves that the catalyst of the present invention has high catalytic activity.

[0171] Test 4:

[0172] In order to verify the stability of the catalyst, the catalytic activity was tested at 400 °C for 30 hours. The test results are as follows: Figure 2 As shown. Figure 2 It can be seen that within the 30-hour test period, the catalyst of Example 1 has a relatively high catalytic activity, and the removal rate of chlorinated volatile organic compounds is substantially maintained at 100%, showing good stability, that is, having good chlorine resistance.

[0173] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that are not substantially different from the literal description of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing a catalyst for treating chlorinated volatile organic compounds, characterized in that: The following steps are involved: (1) Preparation of core-shell structure carriers: preparing cerium oxide cores; An yttrium oxide layer, a zirconium oxide layer, and a silicon oxide layer are sequentially coated on the surface of the cerium oxide core to obtain a carrier; (2) Multi-metal phase active component loading: The carrier is placed in hydrogen peroxide for treatment to obtain a pretreated carrier; The pretreated carrier is added to an ethanol solution, citric acid is added, and the temperature is raised to react to obtain a hydroxylated carrier; Cobaltous oxide and metal palladium are loaded on the hydroxylation carrier in sequence to obtain a catalyst.

2. The method for preparing a catalyst for treating chlorinated volatile organic compounds according to claim 1, wherein: The preparation process of cerium oxide core includes the following steps: A 30-35 wt% cerium nitrate hexahydrate solution was mixed with urea and trisodium citrate, and the molar ratio of cerium ion, urea and trisodium citrate was controlled to be 1:4:(0.15-0.25), and the mixture was 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 into an autoclave, heated to 115-125°C, reacted for 1 hour, then heated to 175-180°C, reacted for 20-22 hours, and cooled to room temperature after the reaction. The reaction solution was centrifuged, and the centrifugal precipitate was washed and dried and placed in a muffle furnace. Under an air atmosphere, the temperature was first raised to 550°C at a rate of 2°C / min and kept warm for 1.5-2 hours, then heated to 950°C at a rate of 5°C / min and kept warm for 4.5-5 hours. After the calcination was completed, the solution 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 a cerium oxide core.

3. The method for preparing a catalyst for treating chlorinated volatile organic compounds according to claim 1, wherein: The yttrium oxide coating process includes the following steps: Yttrium acetylacetonate is dissolved in anhydrous ethanol, and then acetylacetone is added, followed by deionized water at a rate of 0.1 ml / min, with the mass ratio of yttrium acetylacetonate to deionized water controlled to be (0.9-1):(0.05-0.08), and the amount of acetylacetone added controlled to be 10-15% of the molar amount of yttrium acetylacetonate. The mixture is hydrolyzed at room temperature for 10-20 minutes to obtain a transparent sol; The transparent sol is added to anhydrous ethanol of cerium oxide, and the mass ratio of yttrium acetylacetonate and cerium oxide is controlled to be (0.9-1):

10. The temperature is raised to 70°C under a nitrogen atmosphere and refluxed for 3-4 hours. The gel obtained by the reaction is aged at room temperature for 12 hours and then centrifuged. The centrifugal precipitate is dried and placed in a muffle furnace. The temperature is raised to 300°C at a rate of 1°C / min under an air atmosphere, kept warm for 1 hour, then raised to 600°C at a rate of 2°C / min, kept warm for 2 hours, and finally cooled to room temperature with the furnace to obtain cerium oxide / yttrium oxide powder.

4. The method for preparing a catalyst for treating chlorinated volatile organic compounds according to claim 1, wherein: The coating process of the zirconium oxide layer includes the following steps: Cerium oxide / yttrium oxide powder and polyethylene glycol 4000 are dispersed in deionized water, zirconium oxychloride octahydrate and urea are added and mixed evenly, and the mass ratio of cerium oxide / yttrium oxide powder, polyethylene glycol 4000, zirconium oxychloride octahydrate and urea is controlled to be (0.1-0.5): (0.001-0.005): (0.05-0.25): (0.5-2.0), and the pH of the reaction system is adjusted to 2-4. The obtained mixed solution is transferred to an autoclave, reacted at 150-180°C for 12-24 hours, cooled to room temperature after the reaction, filtered, and the precipitate is dried and calcined at 450-550°C for 1-2 hours.

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

6. The method for preparing a catalyst for treating chlorinated volatile organic compounds according to claim 1, characterized in that: The concentration of the 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 mass of the pretreatment carrier. The temperature of the temperature-raising reaction is 70° C., and the time is 3-4 h.

7. The method for preparing a catalyst for treating chlorinated volatile organic compounds according to claim 1, characterized in that: The process of loading cobalt trioxide on a carrier includes the following steps: The hydroxylated carrier is added to a cobalt nitrate solution with a concentration of 0.4-0.5 mol / L, the solid-liquid ratio is controlled to be 1 g:1 ml, and the carrier is impregnated at room temperature for 2-3 hours. After the impregnation, the solid is taken out and first pre-cooled at -50°C for 1 hour, then dried at -30°C and a vacuum degree of 10 Pa for 10-12 hours, and finally dried at room temperature and a vacuum degree of 1 Pa for 5-6 hours; the dried solid is kept at 250°C in an air atmosphere for 2 hours, and then heated to 400°C and kept for 4 hours to obtain a carrier loaded with cobalt tetroxide.

8. The method for preparing a catalyst for treating chlorinated volatile organic compounds according to claim 1, wherein: The process of loading metallic palladium on a carrier comprises the following steps: A carrier loaded with cobalt tetroxide is added to a mixed solution of tetrachloropalladium acid and citric acid, wherein the molar ratio of tetrachloropalladium acid to citric acid in the mixed solution is 1:2, the concentration of tetrachloropalladium acid is 10-15wt%, and the solid-liquid ratio is controlled to be 1g:(4-6)ml. The mixture is immersed at room temperature for 20-30 minutes, then heated to 50°C, stirred and adsorbed at a speed of 200-300rpm for 1-2 hours, and then centrifuged. The precipitate is washed and dried. The dried solid is reduced at 500°C for 2 hours in a mixed gas of hydrogen and nitrogen with a volume ratio of hydrogen to nitrogen controlled to be 5:95 to obtain a catalyst.

9. Use of the catalyst prepared by the method according to any one of claims 1 to 9 in treating chlorinated volatile organic compounds, characterized in that: The following steps are involved: The catalyst is filled in a fixed bed reactor, and a reaction gas consisting of dichloromethane, nitrogen and oxygen is introduced into the fixed bed reactor to perform a catalytic oxidation reaction.

10. Use of the catalyst according to claim 10 in treating chlorinated volatile organic compounds, characterized in that: The concentrations of dichloromethane and oxygen in the reaction gas are 1000-3000ppm and 18-22v%, respectively. Nitrogen is the balance gas, and the gas space velocity is 15000-20000ml·g -1 ·h -1 ; The catalyst dosage is 0.08-0.15g, and the reaction temperature is 200-400℃.

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