A mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation

Abstract

This invention relates to a mud-based molecular sieve-supported α-MnO2 catalyst based on a dual regulation of acid treatment and metal impregnation. The method uses activated mud as raw material, synthesizing Na-type ZSM-5 molecular sieves via hydrothermal crystallization, followed by ion exchange to obtain H-type molecular sieves. Subsequently, α-MnO2 is loaded, and the acidity of the framework is adjusted through weak acid treatment to optimize the pore environment, improve the dispersibility and active site exposure of α-MnO2, and increase Mn content. 4+ The content of Cu promotes the generation of surface lattice oxygen and enhances the driving force of redox cycles. Further through Cu... 2+ Fe 3+ Ce 3+ Doping with metal ions enhances oxygen migration and catalytic oxidation capabilities. This catalyst exhibits excellent low-temperature activity, resistance to poisoning, and structural stability in the low-temperature catalytic oxidation of VOCs in oil fields. The process conditions are mild and environmentally friendly, and the raw materials are widely available, making it promising for industrial applications, particularly suitable for waste resource recovery and VOCs pollution control.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental catalysis and solid waste resource utilization, and particularly relates to a supported catalyst and a preparation method thereof, wherein H-type ZSM-5 molecular sieves synthesized from oilfield mud resources are used as carriers, and then α-MnO2 is loaded and modified by acid and metal impregnation. The catalyst is mainly used for efficient low-temperature catalytic oxidation treatment of oilfield VOCs, and is particularly suitable for treatment of typical volatile organic compounds such as oilfield associated gas or light hydrocarbon waste gas. The technology takes into account pollutant emission reduction and resource recycling of oilfield waste, and has good engineering popularization value. TECHNICAL BACKGROUND

[0002] With the continuous improvement of oil and gas field development intensity, a large amount of volatile organic compounds (VOCs) generated in the oilfield production process has become a major source of air pollution that needs to be treated. In particular, saturated hydrocarbons such as propane, butane and pentane, which are representative of oilfield VOCs, not only have a low reaction initiation temperature and high toxicity, but also are easy to undergo photochemical reactions with NO x under sunlight to form secondary pollutants such as ozone and PM 2.5 Therefore, developing an efficient catalyst suitable for oilfield special VOCs has become a problem that needs to be solved.

[0003] Low-temperature catalytic oxidation is a VOCs treatment technology with high treatment efficiency, wide applicability and less secondary pollution, and the performance of the catalyst plays a decisive role in reaction activity and stability. ZSM-5 molecular sieves have good application potential in VOCs catalytic oxidation due to their regular pore structure, excellent thermal stability and tunability. However, the current commercial ZSM-5 raw material has a high cost and a complex preparation process, which limits its popularization and application in large-scale industrial waste gas treatment.

[0004] A large amount of mud solid waste generated in the drilling, oil production and storage and transportation processes of oilfields is rich in silicon and aluminum components, and is a potential precursor resource for synthesizing molecular sieves. The use of such mud resources for green preparation of ZSM-5 molecular sieves not only greatly reduces the cost of catalyst materials, but also helps to realize harmless and resourceful treatment of solid waste, in line with the concept of green and low-carbon development.

[0005] In order to further improve the catalytic performance, the present application adopts a multi-step regulation strategy, first loads α-MnO2 on the surface of mud-based ZSM-5 molecular sieves by an improved hydrothermal-calcination method to construct catalytically active oxygen species sites; then adjusts the framework acidity by acid treatment to optimize the pore environment, improve the dispersion of α-MnO2 and the exposure degree of active sites, increase the content of Mn 4+ in α-MnO2, and promote the generation of a higher concentration of surface lattice oxygen species, thereby enhancing the catalytic activity of the catalyst Mn 4+ and Mn 3+The redox cycle driving force between Mn and Mn is promoted by introducing transition metals such as Cu, Fe and Ce into the catalyst through a metal salt impregnation method, the oxygen migration ability is strengthened, the active oxygen free radicals are generated, and the low-temperature activity and anti-poisoning performance of the catalyst are significantly improved.

[0006] The catalyst preparation process is controllable, the raw materials are cheap, the prepared material has stable structure, and the material has excellent low-temperature catalytic oxidation ability of light hydrocarbon VOCs, strong anti-coking and anti-sulfur poisoning ability, and is especially suitable for complex working conditions such as high humidity and high carbon load in oil field VOCs treatment, and has good application prospect and popularization value. SUMMARY

[0007] The preparation method of the catalyst provided by the application mainly comprises the following steps: a H-type ZSM-5 molecular sieve synthesized from mud resources is used as a carrier, alpha-MnO2 is first loaded, then the acid environment is adjusted through acid treatment, and finally transition metal ions such as Cu 2+ , Fe 3+ or Ce 3+ are introduced into the molecular sieve supported catalyst through a metal salt impregnation method. 4+ The dispersion and activity site exposure degree of alpha-MnO2 are improved through acid treatment, the content of Mn in alpha-MnO2 is increased, the generation of a higher concentration of surface lattice oxygen substances is promoted, and the redox cycle driving force between Mn and Mn is enhanced. 4+ The active center distribution density is controlled through appropriate concentration gradient control. Finally, the structure is stabilized through hydrothermal reaction and calcination, and the synergistic enhancement of the active components is realized. The catalyst provided by the application has excellent propane low-temperature catalytic oxidation performance, good anti-poisoning ability and high-temperature stability, and is especially suitable for continuous catalytic oxidation treatment process under high load and humid conditions in the treatment of oil field VOCs (mainly light hydrocarbon components). 3+ The preparation method of the catalyst provided by the application mainly comprises the following steps:

[0008] S1, synthesis of ZSM-5 molecular sieve

[0009] The dried and calcined oil field drilling mud is selected as a silicon-aluminum source, a silicon source, an organic amine template agent, a seed crystal and deionized water are supplemented, a precursor colloid system is prepared, the system is stirred uniformly and then transferred into a hydrothermal reaction kettle, crystallization is carried out at a controlled temperature for a certain time, and a crude product is obtained. The organic template is removed through solid-liquid separation, neutralization and washing, drying and high-temperature calcination, and Na-type ZSM-5 molecular sieve is prepared.

[0010] S2, preparation of H-type molecular sieve

[0011] The Na type ZSM-5 molecular sieve is dispersed in an ammonium chloride or ammonium nitrate solution, and a plurality of ion exchange reactions are carried out by water bath stirring to exchange Na in the framework into NH4 + + After being washed, freeze-dried and high-temperature calcination for ammonia removal, the H type ZSM-5 molecular sieve is obtained.

[0012] S3, loading of α-MnO2

[0013] Potassium permanganate and ammonium oxalate are dissolved in water to form a redox system, and a nano-sized MnO2 precipitate is generated by reaction under a warm water bath condition; then the H type ZSM-5 molecular sieve is added into the reaction system, and after being uniformly stirred and mixed, the system is transferred into an autoclave for reaction, so that the α-MnO2 is uniformly loaded into the molecular sieve carrier; and the product is subjected to centrifugation, water washing, freeze-drying and moderate calcination treatment to obtain a supported material.

[0014] S4, acid modification treatment

[0015] The supported material prepared in S3 is soaked in a dilute acid solution with different concentrations, and after being treated for a certain time under stirring or ultrasonic assistance, the material is washed to neutral and then dried. This process can adjust the acid distribution of the molecular sieve, remove weak acid sites and part of the exchanged metal, and improve the synergistic dispersibility of the active components.

[0016] S5, metal salt impregnation modification

[0017] The acid-modified supported catalyst is placed in a metal salt solution with a certain concentration, and after being impregnated for a period of time, the catalyst is separated by centrifugation or suction filtration, washed, dried and calcined to obtain a final mud-based molecular sieve supported α-MnO2 catalyst which is subjected to acid treatment and metal impregnation double regulation.

[0018] Optional parameter settings:

[0019] Optionally, the crystallization temperature in the molecular sieve synthesis process is 150-200 DEG C, and the time is 36-60 h;

[0020] Optionally, the template removal calcination temperature is 500-600 DEG C, and the time is 3-6 h;

[0021] Optionally, the ion exchange liquid is 1 mol / L of NH4Cl or NH4NO3, the exchange temperature is 60-90 DEG C, the time is 1-2 h each time, and the exchange is repeated 2-4 times;

[0022] Optionally, in the preparation process of the supported catalyst, the water bath reaction temperature is 50-70 DEG C, the hydrothermal reaction temperature is 140-180 DEG C, the time is 8-16 h, the calcination temperature is set to 0-400 DEG C, the temperature rising rate is 3-10 DEG C / min, and the holding time is 1-3 h;

[0023] ​Optionally, the acid-modifying solution can be hydrochloric acid, sulfuric acid, acetic acid, etc., with a concentration of 0.01-0.5 mol / L, a liquid-solid ratio of 3:500-10:500, and a modification time of 3-12 h;

[0024] Optionally, the metal salt is selected from nitrates or sulfates, etc., with a solution concentration of 0.01-0.1 mol / L, an impregnation time of 3-12 h, a calcination temperature of 200-400℃, a heating rate of 3-10℃ / min, and a holding time of 1-3 h. Attached Figure Description

[0025] Figure 1 A flowchart of the preparation method provided for an example of the present invention;

[0026] Figure 2 Scanning electron microscope image of a mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation, provided in Example 4 of this invention;

[0027] Figure 3 This is a transmission electron microscope (TEM) image of a mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation, provided in Example 4 of this invention.

[0028] Figure 4 XPS diagrams of the Mn 2p orbitals of the mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation provided in Examples 2 and 3 of this invention;

[0029] Figure 5 The N2 adsorption-desorption isotherms and pore size distribution diagrams of α-MnO2 catalyst supported on mud-based molecular sieves based on dual regulation of acid treatment and metal impregnation provided in Examples 2, 3, and 4 of this invention are shown.

[0030] Figure 6 The graph shows the degradation efficiency of propane by the prepared mud-based molecular sieve-supported α-MnO2 catalyst under different temperatures, which is subject to dual regulation by acid treatment and metal impregnation. Detailed Implementation

[0031] Example 1: A mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation and its preparation method.

[0032] 5g of mud (containing 41.89% SiO2, 13.62% Al2O3, 4.27% Fe2O3, and 2.85% MgO) was physically mixed with 1g of NaOH for 15 min and placed in a zirconia boat. The mixture was heated to 900℃ at a rate of 5℃ / min and calcined in air for 120 min. The activated mud precursor was then mixed with 6.7g of silica gel, 4.03g of n-butylamine, 0.378g of seed crystals, and 70ml of deionized water. The mixture was stirred at room temperature for 3 h, and the gel was then transferred to a stainless steel crystallization vessel lined with polytetrafluoroethylene and hydrothermally crystallized in an oven at 170℃ for 48 h. After crystallization, the mixture was cooled, filtered to remove the mother liquor, and the solid product was washed until neutral. It was then freeze-dried and finally calcined in a muffle furnace at 550℃ for 4 h to remove the template agent, yielding Na-type ZSM-5 molecular sieve. The Na-type molecular sieve was subjected to three ion exchanges at 80℃ with a 1 mol / L NH4Cl solution (liquid to solid ratio of 10 ml / g), each for 1.5 h. Then, it was freeze-dried and calcined at 550℃ for 4 h to obtain the H-type ZSM-5 molecular sieve.

[0033] 498 mg of potassium permanganate was dissolved in 25 mL of deionized water, and 227 mg of ammonium oxalate monohydrate was dissolved in 40 mL of deionized water. Each solution was stirred thoroughly for 30 min, and these solutions were designated as solution A and solution B, respectively. Next, solution A was placed in a 60°C constant temperature water bath, and solution B was slowly added to solution A. The mixture was stirred with a magnetic stirrer for another 30 min. After stirring, molecular sieves were added, and the mixture was stirred until dry to the required temperature. The resulting product was then dried at 90°C. Finally, the dried product was calcined in a muffle furnace at 300°C to obtain the supported catalyst.

[0034] Example 2: A mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation and its preparation method.

[0035] The difference between this embodiment and Embodiment 1 is the load method used.

[0036] 5g of mud (containing 41.89% SiO2, 13.62% Al2O3, 4.27% Fe2O3, and 2.85% MgO) was physically mixed with 1g of NaOH for 15 min and placed in a zirconia boat. The mixture was heated to 900℃ at a rate of 5℃ / min and calcined in air for 120 min. The activated mud precursor was then mixed with 6.7g of silica gel, 4.03g of n-butylamine, 0.378g of seed crystals, and 70ml of deionized water. The mixture was stirred at room temperature for 3 h, and the gel was then transferred to a stainless steel crystallization vessel lined with polytetrafluoroethylene and hydrothermally crystallized in an oven at 170℃ for 48 h. After crystallization, the mixture was cooled, filtered to remove the mother liquor, and the solid product was washed until neutral. It was then freeze-dried and finally calcined in a muffle furnace at 550℃ for 4 h to remove the template agent, yielding Na-type ZSM-5 molecular sieve. The Na-type molecular sieve was subjected to three ion exchanges at 80℃ with a 1 mol / L NH4Cl solution (liquid to solid ratio of 10 ml / g), each for 1.5 h. Then, it was freeze-dried and calcined at 550℃ for 4 h to obtain the H-type ZSM-5 molecular sieve.

[0037] 498 mg of potassium permanganate was dissolved in 25 mL of deionized water, and 227 mg of ammonium oxalate monohydrate was dissolved in 40 mL of deionized water. Each solution was stirred thoroughly for 30 min, and these solutions were designated as solution A and solution B, respectively. Next, solution A was placed in a 60°C constant temperature water bath, and solution B was slowly added to it. Stirring was continued for 30 min using a magnetic stirrer. After stirring, molecular sieves were added, and the mixture was stirred at room temperature for 40 min. The resulting mixture was then transferred to a 100 mL hydrothermal reactor and reacted at 160°C for 12 h. After the reaction was complete, the product was washed multiple times by centrifugation with deionized water, followed by freeze-drying. Finally, the dried product was calcined in a muffle furnace at 300°C to obtain the supported catalyst.

[0038] Performance testing revealed that the supported catalyst prepared by the hydrothermal method (Example 2) exhibited significantly improved catalytic performance compared to the supported catalyst prepared by the calcination method (Example 1). 90 (From 350℃ to 320℃)

[0039] Example 3: A mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation and its preparation method.

[0040] The difference between this embodiment and Embodiment 2 is that acid modification was performed.

[0041] 5g of mud (containing 41.89% SiO2, 13.62% Al2O3, 4.27% Fe2O3, and 2.85% MgO) was physically mixed with 1g of NaOH for 15 min and placed in a zirconia boat. The mixture was heated to 900℃ at a rate of 5℃ / min and calcined in air for 120 min. The activated mud precursor was then mixed with 6.7g of silica gel, 4.03g of n-butylamine, 0.378g of seed crystals, and 70ml of deionized water. The mixture was stirred at room temperature for 3 h, and the gel was then transferred to a stainless steel crystallization vessel lined with polytetrafluoroethylene and hydrothermally crystallized in an oven at 170℃ for 48 h. After crystallization, the mixture was cooled, filtered to remove the mother liquor, and the solid product was washed until neutral. It was then freeze-dried and finally calcined in a muffle furnace at 550℃ for 4 h to remove the template agent, yielding Na-type ZSM-5 molecular sieve. The Na-type molecular sieve was subjected to three ion exchanges at 80℃ with a 1 mol / L NH4Cl solution (liquid to solid ratio of 10 ml / g), each for 1.5 h. Then, it was freeze-dried and calcined at 550℃ for 4 h to obtain the H-type ZSM-5 molecular sieve.

[0042] 498 mg of potassium permanganate was dissolved in 25 mL of deionized water, and 227 mg of ammonium oxalate monohydrate was dissolved in 40 mL of deionized water. Each solution was stirred thoroughly for 30 min, and these solutions were designated as solution A and solution B, respectively. Next, solution A was placed in a 60°C constant temperature water bath, and solution B was slowly added to it. Stirring was continued for 30 min using a magnetic stirrer. After stirring, molecular sieves were added, and the mixture was stirred at room temperature for 40 min. The resulting mixture was then transferred to a 100 mL hydrothermal reactor and reacted at 160°C for 12 h. After the reaction was complete, the product was washed multiple times by centrifugation with deionized water, followed by freeze-drying. Finally, the dried product was calcined in a muffle furnace at 300°C to obtain the supported catalyst.

[0043] 0.3 g of the supported catalyst was weighed and dissolved in 50 ml of 0.3 mol / L dilute hydrochloric acid solution. After ultrasonic stirring for 20 min, the solution was placed on a magnetic stirrer and stirred continuously at room temperature for 6 h. The solution was then washed with distilled water by centrifugation until neutral and freeze-dried to obtain the acidified supported catalyst.

[0044] Performance testing revealed that the performance of the acid-modified catalyst was improved compared to the unmodified catalyst. 90 The temperature was reduced from 320℃ to 276℃. BET testing revealed that acid modification opened some of the original micropores, increasing the catalyst's gas adsorption capacity. XPS testing showed that the acid-modified catalyst (Mn...) 3+ ) / Mn 4+ The decrease in the ratio indicates that acid modification can significantly increase the Mn content in manganese-based catalysts.4+ The content of oxygen vacancies and active oxygen is increased, and the catalyst has more oxygen vacancies and higher redox activity.

[0045] Example 4: A mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation and its preparation method.

[0046] The difference between this embodiment and Embodiment 3 is that metal modification was performed.

[0047] 5g of mud (containing 41.89% SiO2, 13.62% Al2O3, 4.27% Fe2O3, and 2.85% MgO) was physically mixed with 1g of NaOH for 15 min and placed in a zirconia boat. The mixture was heated to 900℃ at a rate of 5℃ / min and calcined in air for 120 min. The activated mud precursor was then mixed with 6.7g of silica gel, 4.03g of n-butylamine, 0.378g of seed crystals, and 70ml of deionized water. The mixture was stirred at room temperature for 3 h, and the gel was then transferred to a stainless steel crystallization vessel lined with polytetrafluoroethylene and hydrothermally crystallized in an oven at 170℃ for 48 h. After crystallization, the mixture was cooled, filtered to remove the mother liquor, and the solid product was washed until neutral. It was then freeze-dried and finally calcined in a muffle furnace at 550℃ for 4 h to remove the template agent, yielding Na-type ZSM-5 molecular sieve. The Na-type molecular sieve was subjected to three ion exchanges at 80℃ with a 1 mol / L NH4Cl solution (liquid to solid ratio of 10 ml / g), each for 1.5 h. Then, it was freeze-dried and calcined at 550℃ for 4 h to obtain the H-type ZSM-5 molecular sieve.

[0048] 498 mg of potassium permanganate was dissolved in 25 mL of deionized water, and 227 mg of ammonium oxalate monohydrate was dissolved in 40 mL of deionized water. Each solution was stirred thoroughly for 30 min, and these solutions were designated as solution A and solution B, respectively. Next, solution A was placed in a 60°C constant temperature water bath, and solution B was slowly added to it. Stirring was continued for 30 min using a magnetic stirrer. After stirring, molecular sieves were added, and the mixture was stirred at room temperature for 40 min. The resulting mixture was then transferred to a 100 mL hydrothermal reactor and reacted at 160°C for 12 h. After the reaction was complete, the product was washed multiple times by centrifugation with deionized water, followed by freeze-drying. Finally, the dried product was calcined in a muffle furnace at 300°C to obtain the supported catalyst.

[0049] 0.3 g of the supported catalyst was weighed and dissolved in 50 ml of 0.3 mol / L dilute hydrochloric acid solution. After ultrasonic stirring for 20 min, the solution was placed on a magnetic stirrer and stirred continuously at room temperature for 6 h. The solution was then washed with distilled water by centrifugation until neutral and freeze-dried to obtain the acidified supported catalyst.

[0050] 0.3g of the acidified supported catalyst was dissolved in 50ml of 0.05mol / L copper nitrate solution and stirred continuously at room temperature for 8h. The solution was then washed four times by centrifugation with distilled water, freeze-dried, and calcined at 300℃ for 2h to obtain the composite modified supported catalyst.

[0051] Example 5: A mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation and its preparation method.

[0052] The difference between this embodiment and Embodiment 4 is the type of metal salt and the immersion time.

[0053] 5g of mud (containing 41.89% SiO2, 13.62% Al2O3, 4.27% Fe2O3, and 2.85% MgO) was physically mixed with 1g of NaOH for 15 min and placed in a zirconia boat. The mixture was heated to 900℃ at a rate of 5℃ / min and calcined in air for 120 min. The activated mud precursor was then mixed with 6.7g of silica gel, 4.03g of n-butylamine, 0.378g of seed crystals, and 70ml of deionized water. The mixture was stirred at room temperature for 3 h, and the gel was then transferred to a stainless steel crystallization vessel lined with polytetrafluoroethylene and hydrothermally crystallized in an oven at 170℃ for 48 h. After crystallization, the mixture was cooled, filtered to remove the mother liquor, and the solid product was washed until neutral. It was then freeze-dried and finally calcined in a muffle furnace at 550℃ for 4 h to remove the template agent, yielding Na-type ZSM-5 molecular sieve. The Na-type molecular sieve was subjected to three ion exchanges at 80℃ with a 1 mol / L NH4Cl solution (liquid to solid ratio of 10 ml / g), each for 1.5 h. Then, it was freeze-dried and calcined at 550℃ for 4 h to obtain the H-type ZSM-5 molecular sieve.

[0054] 498 mg of potassium permanganate was dissolved in 25 mL of deionized water, and 227 mg of ammonium oxalate monohydrate was dissolved in 40 mL of deionized water. Each solution was stirred thoroughly for 30 min, and these solutions were designated as solution A and solution B, respectively. Next, solution A was placed in a 60°C constant temperature water bath, and solution B was slowly added to it. Stirring was continued for 30 min using a magnetic stirrer. After stirring, molecular sieves were added, and the mixture was stirred at room temperature for 40 min. The resulting mixture was then transferred to a 100 mL hydrothermal reactor and reacted at 160°C for 12 h. After the reaction was complete, the product was washed multiple times by centrifugation with deionized water, followed by freeze-drying. Finally, the dried product was calcined in a muffle furnace at 300°C to obtain the supported catalyst.

[0055] 0.3 g of the supported catalyst was weighed and dissolved in 50 ml of 0.3 mol / L dilute hydrochloric acid solution. After ultrasonic stirring for 20 min, the solution was placed on a magnetic stirrer and stirred continuously at room temperature for 6 h. The solution was then washed with distilled water by centrifugation until neutral and freeze-dried to obtain the acidified supported catalyst.

[0056] 0.3 g of the acidified supported catalyst was dissolved in 50 ml of 0.1 mol / L cerium nitrate solution and stirred continuously at room temperature for 4 h. The solution was then washed four times by centrifugation with distilled water, freeze-dried, and calcined at 300 °C for 2 h to obtain the composite modified supported catalyst.

[0057] Example 6: A mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation and its preparation method.

[0058] The difference between this embodiment and Embodiment 5 is the type of metal salt.

[0059] 5g of mud (containing 41.89% SiO2, 13.62% Al2O3, 4.27% Fe2O3, and 2.85% MgO) was physically mixed with 1g of NaOH for 15 min and placed in a zirconia boat. The mixture was heated to 900℃ at a rate of 5℃ / min and calcined in air for 120 min. The activated mud precursor was then mixed with 6.7g of silica gel, 4.03g of n-butylamine, 0.378g of seed crystals, and 70ml of deionized water. The mixture was stirred at room temperature for 3 h, and the gel was then transferred to a stainless steel crystallization vessel lined with polytetrafluoroethylene and hydrothermally crystallized in an oven at 170℃ for 48 h. After crystallization, the mixture was cooled, filtered to remove the mother liquor, and the solid product was washed until neutral. It was then freeze-dried and finally calcined in a muffle furnace at 550℃ for 4 h to remove the template agent, yielding Na-type ZSM-5 molecular sieve. The Na-type molecular sieve was subjected to three ion exchanges at 80℃ with a 1 mol / L NH4Cl solution (liquid to solid ratio of 10 ml / g), each for 1.5 h. Then, it was freeze-dried and calcined at 550℃ for 4 h to obtain the H-type ZSM-5 molecular sieve.

[0060] 498 mg of potassium permanganate was dissolved in 25 mL of deionized water, and 227 mg of ammonium oxalate monohydrate was dissolved in 40 mL of deionized water. Each solution was stirred thoroughly for 30 min, and these solutions were designated as solution A and solution B, respectively. Next, solution A was placed in a 60°C constant temperature water bath, and solution B was slowly added to it. Stirring was continued for 30 min using a magnetic stirrer. After stirring, molecular sieves were added, and the mixture was stirred at room temperature for 40 min. The resulting mixture was then transferred to a 100 mL hydrothermal reactor and reacted at 160°C for 12 h. After the reaction was complete, the product was washed multiple times by centrifugation with deionized water, followed by freeze-drying. Finally, the dried product was calcined in a muffle furnace at 300°C to obtain the supported catalyst.

[0061] 0.3 g of the supported catalyst was weighed and dissolved in 50 ml of 0.3 mol / L dilute hydrochloric acid solution. After ultrasonic stirring for 20 min, the solution was placed on a magnetic stirrer and stirred continuously at room temperature for 6 h. The solution was then washed with distilled water by centrifugation until neutral and freeze-dried to obtain the acidified supported catalyst.

[0062] 0.3g of the acidified supported catalyst was dissolved in 50ml of 0.1mol / L ferric nitrate solution and stirred continuously at room temperature for 4h. The solution was then washed four times by centrifugation with distilled water, freeze-dried, and calcined at 300℃ for 2h to obtain the composite modified supported catalyst.

[0063] Experimental Example 1

[0064] Low-temperature catalytic oxidative degradation of propane using mud-based molecular sieve supported catalysts in Examples 1-6:

[0065] Weigh out 0.2g of the mud-based molecular sieve supported catalyst from Examples 1-6 and load it into a U-shaped reactor. Place the U-shaped reactor into a low-temperature catalytic oxidation test apparatus, setting the initial propane concentration to 1080 mg·m³. -3 And control the mass hourly space velocity to 15000 mL·g -1 ·h -1 The catalyst was first allowed to adsorb at room temperature without heating until adsorption equilibrium was reached. Then, the temperature was increased, and gas chromatography was used to test the degradation rate of propane at different temperatures.

[0066] Depend on Figure 4 It can be seen that the catalysts prepared in Examples 1-6 have different low-temperature catalytic oxidation activities, among which the catalyst prepared in Example 1 has higher low-temperature catalytic oxidation activity for propane than the catalysts in Examples 2, 3, and 4. Example 4 achieved a propane degradation rate of 90% at 266°C.

[0067] The applicant declares that the above embodiments are used to illustrate the detailed operation and process flow of the present invention, but are not limited to the above detailed operation and process flow. Those skilled in the art should understand that any equivalent structural or process transformations made using the present invention specification, or direct or indirect applications in other related technical fields, fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a mud-based molecular sieve-supported α-MnO2 catalyst based on dual regulation of acid treatment and metal impregnation, comprising the following steps: S1. Mud precursor activation treatment: After drying the mud, it is mixed evenly with an alkali source and then calcined at high temperature in air at a certain heating rate to achieve activation, thus obtaining an activated mud precursor. Synthesis of S2 and Na-type ZSM-5 molecular sieves: The activated mud is mixed with silicon source, organic template agent, seed crystal and deionized water in a certain proportion and stirred evenly to form a gel system with a suitable molar ratio. It is then transferred to a stainless steel crystallization kettle with a polytetrafluoroethylene liner and crystallized at a certain temperature for a certain time to obtain the initial product. After cooling, filtering, washing to neutrality, drying and calcining to remove the template agent, Na-type ZSM-5 molecular sieve is obtained. Synthesis of S3 and H-type molecular sieves: The obtained Na-type ZSM-5 molecular sieve was subjected to multiple ion exchange treatments with ammonium salt solution under certain temperature conditions, and then H-type ZSM-5 molecular sieve was obtained through drying and calcination processes. S4, α-MnO2 loading: Potassium permanganate and a reducing agent such as ammonium oxalate were dissolved in deionized water in a certain proportion to form two solutions. They were mixed and reacted under water bath conditions to generate α-MnO2 precursor solution. H-type ZSM-5 molecular sieve obtained in step S3 was added to it and the mixture was stirred for a period of time before being transferred to a hydrothermal reactor for reaction. The product was washed, freeze-dried and calcined to obtain the catalyst supported on α-MnO2. S5, Acid Modification: The catalyst supported on α-MnO2 was impregnated in a dilute acid solution with adjustable acid concentration and appropriate impregnation time. After centrifugation, washing until neutral, and freeze-drying, the acid-modified catalyst was obtained. S6. Metal impregnation modification: The acid-modified catalyst was impregnated in a metal salt solution, where the metal salt was a nitrate or sulfate of copper, iron, or cerium, and the molar ratio of the metal to manganese was within a suitable range. After impregnation, the catalyst was washed, freeze-dried, and calcined to obtain the metal-modified catalyst.

2. The method according to claim 1, characterized in that: The mass ratio of the mud to NaOH is controlled within a certain range, the calcination temperature is 800-950℃, and the time is not less than 1 hour.

3. The method according to claim 1, characterized in that: The molar ratio of the ZSM-5 molecular sieve is SiO2 : Al2O3 : template agent : H2O = 1 : (0.02-0.06) : (0.2-0.5) : (20-30), the crystallization temperature is 150-200℃, the crystallization time is 36-60h, the calcination temperature is 500-600℃, and the calcination time is 3-6 hours.

4. The method according to claim 1, characterized in that: In the ion exchange step, the concentration of the ammonium salt solution is 0.5-2 mol / L, the exchange temperature is 60-90℃, the time is 1-2 hours, and the number of exchanges is 2-4 times.

5. The method according to claim 1, characterized in that: The hydrothermal temperature for α-MnO2 loading is 140-180℃, the reaction time is 8-16 h, and the final calcination temperature is 0-400℃.

6. The method according to claim 1, characterized in that: Acid modification uses dilute hydrochloric acid, dilute nitric acid, or acetic acid, with a concentration range of 0.01-0.5 mol / L and an impregnation time of 3-12 h.

7. The method according to claim 1, characterized in that: The concentration of the metal salt solution was controlled at 0.01-0.1 mol / L, the impregnation time was 3-12 h, and the calcination temperature was 200-400℃.

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