Preparation method of ZSM-5 molecular sieve packaged noble metal honeycomb catalyst

Abstract

The invention relates to a preparation method of a ZSM-5 molecular sieve packaged noble metal honeycomb catalyst for organic waste gas catalytic combustion treatment. Comprising the following steps: S1, carrying out water bath on an alkali source and a silicon source to obtain an all-silicon ZSM-5 molecular sieve precursor liquid; s2, alkaline earth metal salt and precious metal salt are mixed to obtain a precious metal complex solution; s3, dropwise adding the solution in S2 and the template agent solution into the gel in S1 at the same time to form ZSM-5 molecular sieve seed crystal colloid; s4, crystallizing the colloid in S3 into a core to obtain a PM / ZSM-5 catalyst master batch; s5, preparing nanoscale coating slurry, and adding PM / ZSM-5 and an auxiliary agent into the slurry; and S6, coating a honeycomb carrier with the slurry obtained in S5, drying, and roasting to obtain the ZSM-5 molecular sieve packaged noble metal honeycomb catalyst. The problems that a noble metal catalyst is prone to poisoning and short in service life in pollution flashover prevention coating waste gas treatment are solved.

Description

Technical Field

[0001] The invention relates to the preparation of a catalyst for catalytic combustion treatment of organic waste gas from specific industrial sources, in particular to a method for preparing a ZSM-5 molecular sieve encapsulated noble metal honeycomb catalyst. Background Art

[0002] In modern society, electricity has become an indispensable part of our lives and a basic industry that affects the development of contemporary economy. However, in the use of high-voltage equipment, encountering humid weather (fog, morning dew, drizzle, etc.) will cause arc breakdown of the insulating medium, causing serious equipment damage and accidents, which is the so-called pollution flashover. Therefore, anti-pollution flashover treatment of power transmission and transformation equipment is one of the important measures taken to ensure the normal operation of power equipment and the safety and stability of the power grid, and it must be taken seriously and solved in the operation of power equipment. At present, the most commonly used anti-pollution flashover method is to coat insulators with room temperature vulcanized silicone rubber (RTV) coating. Due to its unique and excellent hydrophobicity and hydrophobic migration, RTV forms a layer of film after curing on the surface of the insulator, thereby avoiding the formation of a continuous water film on the surface of the insulator and reducing the occurrence of pollution flashover accidents in special weather. RTV silicone rubber coating contains organic substances such as trichloroethylene, tetrachloroethylene, and silane, and other harmful small molecules will also be produced during the rubber vulcanization process. A large amount of organic waste gas will volatilize during spraying, which will pollute the atmospheric environment.

[0003] In recent years, with the increasingly stringent environmental protection requirements, organic waste gas treatment technology has developed rapidly. The mechanical coating industry will produce a large amount of harmful VOCs during spraying, including hydrocarbons, aromatic hydrocarbons, alcohols, esters, ketones, etc. These substances enter the atmosphere and cause serious environmental pollution, affecting air quality, plant and animal growth and human health. In response to this phenomenon, the country has promulgated the "Emission Standards for Comprehensive Control of Air Pollution" since 1997 to limit the emission of VOCs, and the research on industrial organic waste gas treatment technology has emerged. In particular, the application of adsorption concentration + catalytic combustion CO, adsorption concentration + regenerative incineration RTO technology in recent years has solved the centralized control of large air volume and low concentration industrial organic waste gas, which is currently a more advanced treatment method.

[0004] The core of catalytic combustion technology is the performance of the catalyst. A good catalyst must have the characteristics of high catalytic activity, good thermal stability, and long life. Currently, common catalysts are mainly divided into two types: precious metal catalysts and non-precious metal catalysts, and the catalytic combustion of industrial VOCs is still mainly based on precious metal catalysts. Precious metal catalysts use precious metals such as platinum Pt, palladium Pd, and rhodium Rh as active centers. Among them, Pt and Pd are the most widely used. They are often used in high-temperature and high-efficiency catalytic combustion processes. They have good catalytic effects on conventional VOCs. However, when catalyzing anti-fouling flash coatings containing silanes, halogens, and sulfides, it will cause precious metal poisoning and cause catalyst deactivation; non-precious metal catalysts include transition metal oxides such as manganese, tungsten, and molybdenum oxides MO. x Etc., these catalysts show certain resistance to poisoning and selectivity, but their activity and service life are limited, making them difficult to apply industrially. For the catalytic oxidation of complex multi-component high-concentration organic gases containing halogens in the anti-pollution flashover coating spraying industry, the anti-poisoning ability and high temperature resistance of the catalyst are particularly important. The anti-poisoning ability of the catalyst was once improved by increasing the content of precious metals, but on the one hand, excessively high precious metal content easily causes precious metal agglomeration, and the improvement effect is limited; on the other hand, precious metals are expensive, resulting in a large increase in costs. The research and industrialization of non-precious metal-precious metal multi-metal hybrid catalyst technology encapsulated in molecular sieves has good application prospects in the field of exhaust gas treatment of anti-pollution flashover coatings. The introduction of porous molecular sieves as carriers is used to reduce costs and improve performance, and the interaction between components is used to enhance the anti-poisoning ability of the catalyst. Molecular sieves have been widely studied as carriers of active components in the catalyst field.

[0005] CN110292947A discloses an MCM-41 / SAPO-11 composite molecular sieve loaded precious metal catalyst and its preparation method and application. The preparation method of the catalyst comprises the following steps: mixing pure silicon MCM-41 raw powder, a phosphorus source, an aluminum source, a template agent and water and stirring to obtain a uniform gel mixture; then subjecting the mixture to static crystallization, centrifugation, deionized water washing, drying and calcination activation treatments in sequence; and then tableting, crushing and sieving to obtain MCM-41 / SAPO-11 composite molecular sieve particles; using the MCM-41 / SAPO-11 composite molecular sieve particles as catalyst carriers, loading a precious metal precursor by an impregnation method, and then calcining to convert the precious metal precursor into a single precious metal substance, thereby obtaining the MCM-41 / SAPO-11 composite molecular sieve loaded precious metal catalyst.

[0006] CN113275034A discloses a multi-level porous molecular sieve catalyst for VOCs elimination and a preparation method thereof. The preparation of the catalyst comprises the following steps: (1) mixing a silicon source, an aluminum source, an alkali source and water together, stirring evenly, removing alcohol organic matter produced by decomposition, and obtaining a gel; (2) transferring the gel to a reaction kettle and sealing and crystallizing it to obtain a white powdery solid, namely, a ZSM-5 molecular sieve carrier; (3) immersing the ZSM-5 molecular sieve carrier in an aqueous solution containing a soluble salt of a precious metal, and subjecting the mixture to ultrasonication, stirring, standing, drying, and roasting to obtain a multi-level porous molecular sieve catalyst loaded with precious metals.

[0007] The methods of the above patents all disperse the precious metals on the surface of the molecular sieve in the form of loading. On the one hand, the precious metals are easily sintered at high temperatures and have poor stability. On the other hand, the final product of the catalyst with the molecular sieve as the carrier is granular or powdery, with low mass transfer efficiency, and is not suitable for industrial application. Summary of the invention

[0008] In order to solve the above technical problems, the purpose of the present invention is to provide a method for preparing a ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst for anti-pollution flashover coating exhaust gas treatment, so as to solve the problems of easy poisoning and short life of precious metal catalysts in the anti-pollution flashover coating exhaust gas treatment in the power equipment coating industry.

[0009] The preparation method of the ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst of the present invention comprises the following steps:

[0010] S1. Preparation of all-silicon ZSM-5 precursor: dissolve the alkali source in deionized water and stir until fully dissolved to form an alkaline solution; add the silicon source to the alkaline solution, mix and stir for 1-4 hours to form a silicate gel, and let it stand in a water bath at 60-90°C for 1-4 hours to obtain an all-silicon ZSM-5 molecular sieve precursor solution; wherein the molar ratio of SiO2 in the silica sol to OH- in the alkali is 1:(60-80);

[0011] S2. Preparation of precious metal complexes; dissolving alkaline earth metal salt and precious metal salt in deionized water, adding complexing agent, stirring evenly, and heating in a water bath to obtain a precious metal complex solution; wherein the mass ratio of precious metal: alkaline earth metal: complexing agent is 1:(2-5):(0.1-1), the water bath temperature is 60-80°C, and the water bath time is 2-4h;

[0012] S3, preparation of molecular sieve seed crystals loaded with noble metal complexes;

[0013] Take a certain amount of template solution; add the noble metal complex solution and template solution in S2 to the gel of S1 at the same time, control the dropping speed to avoid local reaction; then reflux in an oil bath at 80-160°C for 6-24h to form a ZSM-5 molecular sieve seed colloid wrapped with the noble metal complex; wherein the mass ratio of the noble metal complex to the template is 1:(0.1-1);

[0014] Preparation of S4 and ZSM-5 molecular sieve encapsulated Pt or Pd complex masterbatch;

[0015] The colloid obtained in S3 is transferred into a high-pressure reactor, the reactor is tightened, and placed in an oven, the reaction temperature is set to 100-200°C, and crystallization and nucleation are carried out at a constant temperature for 7-14 days. After the nucleation is completed, it is cooled to room temperature, the reactor is opened for filtration, and the product is washed with deionized water until it is neutral, and solid-liquid separation is performed to obtain a solid product; the solid product is dried at 80-150°C for 4-8 hours to obtain a noble metal catalyst masterbatch with a ZSM-5 molecular sieve encapsulation structure, which is marked as PM / ZSM-5;

[0016] S5. Preparation of honeycomb catalyst coating;

[0017] Add metal oxide, rare earth oxide, deionized water and binder into a stirring tank, blend, stir and grind to prepare nano-scale coating slurry, wherein the weight percentage of each component is 10-30 parts of metal oxide, 10-30 parts of rare earth oxide, 100 parts of deionized water and 1-5 parts of binder; add 1-10 parts of PM / ZSM-5 and 0.1-1 parts of auxiliary agent into the slurry, blend and stir for 1-4 hours and grind for 1-4 hours at room temperature, and adjust the pH range of the system to 3.5-6.5;

[0018] S6. Preparation of honeycomb catalyst;

[0019] The slurry obtained in S5 is coated on a honeycomb carrier, excess slurry is removed by vacuum, hot air drying is performed at 60-150°C, and calcination is performed at 400-600°C under nitrogen protection to obtain a molecular sieve encapsulated precious metal honeycomb catalyst for waste gas treatment of anti-pollution flashover coatings.

[0020] Preferably, the alkali source described in S1 is at least one of NaOH and KOH; the silicon source is at least one of silica sol, ethyl orthosilicate, white carbon black and water glass.

[0021] Preferably, the noble metal salt described in S2 is at least one of platinum nitrate Pt(NO3)2, di(ethanolammonium)hexahydroxyplatinate [HOCH2CH2NH3]2Pt(OH)6, and palladium nitrate Pd(NO3)2.

[0022] Preferably, the alkaline earth metal salt described in S2 is at least one of acetate and nitrate of magnesium, calcium, strontium and barium salts; and the complexing agent is at least one of polyvinyl alcohol PVA, ethylenediaminetetraacetic acid EDTA and polyethylene glycol PEG.

[0023] Preferably, the template agent described in S3 is at least one substance selected from tetraethylammonium hydroxide TEAOH, tetrapropylammonium hydroxide TPAOH, tetrapropylammonium bromide TEAB, ethylenediamine EDA, and n-butylamine solution with a mass concentration of 10% to 50%.

[0024] In the preparation method provided by the present invention, the organic amine is not only a guiding agent and a template agent in the synthesis process of the all-silicon ZSM-5, but also serves as a pH regulator for the precious metal solution, which is an important step to ensure that the precious metal particles are anchored in the ZSM-5. The precious metal cluster complex is encapsulated in the ZSM-5 molecular sieve by the ligand protection method to form a porous ZSM-5 molecular sieve system with highly dispersed precious metals.

[0025] Preferably, the metal oxide in S5 is at least one of Al2O3, TiO2, and ZrO2; the rare earth oxide is at least one of CeO2, La2O3, and Y2O3; and the binder is at least one of silica sol and alumina sol.

[0026] Preferably, the auxiliary agents in S5 include dispersants, pH regulators, and defoamers; the dispersants include one or a mixture of ultrafine barium sulfate and titanium dioxide; the pH regulators include alkali regulators and acid regulators, the alkali regulator is at least one of TEAOH, EDA, and Ba(OH)2, and the added amount accounts for 0.01% to 5% of the total amount of the coating slurry; the acid regulator is at least one of citric acid, oxalic acid, and dilute nitric acid, and the added amount accounts for 0.01% to 5% of the total amount of the coating slurry; the defoamer is at least one of silicone oil, sodium polyether sulfate, and sodium dodecylbenzene sulfonate, accounting for 0.01% to 5% of the total amount of the coating slurry.

[0027] Preferably, the honeycomb carrier in S6 is a cordierite honeycomb ceramic carrier, a glass fiber corrugated honeycomb carrier, or a metal wire mesh honeycomb carrier, with a mesh size of 60-600.

[0028] The present invention also provides the SM-5 molecular sieve encapsulated precious metal honeycomb catalyst prepared by the above method, and its application in the catalytic oxidation treatment of anti-pollution flashover coating exhaust gas.

[0029] The advantages of the present invention are:

[0030] 1. The present invention provides a simple strategy for in-situ synthesis of molecular sieves. The noble metal complex is added before the ZSM-5 molecular sieve crystallizes and nucleates, which can ensure that the noble metal is encapsulated in the pores of the molecular sieve to form a ZSM-5-coated noble metal particle structure, effectively avoiding the agglomeration of the noble metal and enhancing the structural stability of the noble metal particles.

[0031] 2. The precious metal particles encapsulated with ZSM-5 molecular sieve as carrier are smaller and more evenly dispersed, which is conducive to exposing more active sites, thereby improving the utilization rate of nano precious metal particles and greatly improving the catalytic degradation efficiency.

[0032] In view of the catalytic combustion treatment of complex components such as silane, CVOCs and sulfides in the exhaust gas generated by the spraying of anti-pollution flashover coatings in the power equipment manufacturing industry, the precious metal catalyst encapsulated in all-silicon ZSM-5 will preferentially adsorb toxic substances such as silane, halogens, sulfides, etc. in the reaction between ZSM-5 and metal oxides, reducing the adsorption and poisoning reactions of precious metals. At the same time, there is an obvious synergistic effect between the precious metal active components and the metal oxide components, as well as between different rare earth oxides, with high catalytic efficiency and longer service life than ordinary catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The XRD spectra of the samples prepared in Examples 1-3 and Comparative Examples are shown. DETAILED DESCRIPTION

[0034] Example 1

[0035] 1. Weigh 5 g of sodium hydroxide crystals, measure 20 ml of deionized water, add the weighed sodium hydroxide into the deionized water to dissolve, weigh 83 g of silica sol into the alkali solution, stir and mix with a magnetic stirrer for 2 hours, and then stand at 60°C for 2 hours to obtain an all-silicon ZSM-5 molecular sieve precursor gel.

[0036] 2. Add 50 ml of deionized water to a 5L blender, weigh 29.4 g of magnesium nitrate Mg(NO3)2 powder, add it to the blender and stir to dissolve, weigh 3.5 g of polyvinyl alcohol and 100 g of 10% Pt(NO3)2 solution, add it to the blender and stir evenly, and place it in a 65°C water bath for 4 hours to obtain Pt x Mg y (NO3) z Complex solution.

[0037] 3. Weigh 75g of 25% tetraethylammonium hydroxide TEAOH solution, dilute it to twice its volume with deionized water, and use two peristaltic pumps to pump Pt x Mg y (NO3) zand TEAOH were added dropwise to the molecular sieve precursor in step 1 at a rate of 3 ml / min, stirred for 20 min, and refluxed in an oil bath at 135 °C for 12 h to obtain a Pt-loaded x Mg y (NO3) z Complex of ZSM-5 molecular sieve seed colloid.

[0038] 4. The seed colloid was transferred into a high-pressure reactor lined with Teflon, and crystallized at a constant temperature of 160°C for 10 days. After the nucleation was completed, it was cooled to room temperature and filtered, and washed with deionized water until neutral. Then, the solid and liquid were separated, and the solid product was dried at 125°C for 8 hours to obtain a ZSM-5 molecular sieve encapsulated structure of precious metal catalyst masterbatch, marked as Pt x Mg y (NO3) z / ZSM-5.

[0039] 5. Measure 100 ml of deionized water and add it to the stirring tank. At the same time, add 20.4 g of Al2O3, 17.2 g of CeO2, 3.2 g of La2O3, 2.3 g of BaSO4, and 8.2 g of silica sol and mix thoroughly. Stir-grind for 12 hours and add Pt x Mg y (NO3) z / ZSM-5 masterbatch, using citric acid as a pH regulator, continuing the stirring-grinding cycle for 4 hours, adjusting the slurry pH to 6.2, and obtaining a honeycomb catalyst coating slurry; impregnating and coating the coating slurry on a cordierite honeycomb carrier with a specification of 100*100*50 and 200 mesh, vacuuming out excess slurry, and then performing hot air drying at 125°C and calcining at 550°C under nitrogen protection to obtain a molecular sieve encapsulated structure Pt-based honeycomb catalyst for anti-pollution flashover coating exhaust gas treatment (the precious metal accounts for 0.4% of the mass of the entire honeycomb catalyst).

[0040] Example 2

[0041] 1. Weigh 5.6 g of potassium hydroxide crystals, measure 20 ml of deionized water, add the weighed potassium hydroxide into the deionized water to dissolve, weigh 96 g of ethyl orthosilicate and add it to the alkali solution, stir and mix with a magnetic stirrer for 1.5 hours, and then stand at 75°C for 1 hour to obtain an all-silicon ZSM-5 molecular sieve precursor gel.

[0042] 2. Add 60 ml of deionized water to a 5 L blender, weigh 31 g of barium acetate (CH3COO)2Ba powder, add it to the blender and stir to dissolve, weigh 4.5 g of polyvinyl alcohol and 100 g of 15% [HOCH2CH2NH3]2Pt(OH)6 solution, add it to the blender and stir evenly, and place it in a water bath at 85 °C for 3 h to obtain Pt xBa y (CH3COO) z Complex solution.

[0043] 3. Weigh 100g of 25% tetrapropylammonium hydroxide TPAOH solution, dilute it to twice its volume with deionized water, and use two peristaltic pumps to pump Pt x Ba y (CH3COO) z and TPAOH were added dropwise to the molecular sieve precursor in step 1 at a rate of 5 ml / min, stirred for 40 min, and refluxed in an oil bath at 125 °C for 14 h to obtain a Pt-loaded x Ba y (CH3COO) z Complex of ZSM-5 molecular sieve seed colloid.

[0044] 4. The seed colloid was transferred into a high-pressure reactor lined with Teflon, and crystallized at a constant temperature of 180°C for 12 days. After the nucleation was completed, it was cooled to room temperature and filtered, and washed with deionized water until neutral. Then, the solid and liquid were separated, and the solid product was dried at 130°C for 6 hours to obtain a ZSM-5 molecular sieve encapsulated structure of precious metal catalyst masterbatch, marked as Pt x Ba y (CH3COO) z / ZSM-5

[0045] 5. Measure 80 ml of deionized water and pour it into the stirring tank. At the same time, add 18.3 g of Al2O3, 1.7 g of ZrO2, 20.5 g of Ce2O3, 2 g of TiO2, and 10.3 g of aluminum sol and mix thoroughly. Stir-grind for 16 hours and add ZSM-5@Pt x Ba y (CH3COO) z The masterbatch is prepared by using dilute nitric acid HNO3 as a pH regulator, and the stirring-grinding cycle is continued for 4 hours to adjust the slurry pH to 5.5 to obtain a honeycomb catalyst coating slurry; the coating slurry is impregnated and coated on a metal wire mesh honeycomb carrier with a specification of φ150*50 and 200 mesh, and the excess slurry is removed by vacuum, and then hot air drying at 115°C and calcining at 450°C under nitrogen protection are performed to obtain a molecular sieve encapsulated structure Pt-based honeycomb catalyst for anti-pollution flashover coating exhaust gas treatment (the mass ratio of precious metal to honeycomb catalyst is 0.5%).

[0046] Example 3

[0047] 1. Weigh 8 g of sodium hydroxide crystals, measure 40 ml of deionized water, add the weighed sodium hydroxide into the deionized water to dissolve, weigh 104 g of ethyl orthosilicate and add it to the alkali solution, stir with a magnetic stirrer for 3 hours, and then stand at 80°C for 3 hours to obtain an all-silicon ZSM-5 molecular sieve precursor gel.

[0048] 2. Add 80 ml of deionized water to a 5L blender, weigh 42.2 g of strontium nitrate Sr(NO3)2 powder, add it to the blender and stir to dissolve, weigh 5.3 g of EDTA and 80 g of 15.53% Pd(NO3)2 solution, add it to the blender and stir evenly, and place it in a 65°C water bath for 4 hours to obtain Pd x Sr y (NO3) z Complex solution.

[0049] 3. Weigh 60g of 30% n-butylamine solution and dilute it to twice its volume with deionized water. Use two peristaltic pumps to pump Pd x Sr y (NO3) z and n-butylamine were added dropwise to the molecular sieve precursor in step 1 at a rate of 3 ml / min, stirred for 30 min, and refluxed in an oil bath at 145 °C for 10 h to obtain a Pd-loaded x Sr y (NO3) z Complex of ZSM-5 molecular sieve seed colloid.

[0050] 4. The seed colloid was transferred into a high-pressure reactor lined with Teflon, and crystallized at 190°C for 8 days. After the nucleation was completed, it was cooled to room temperature and filtered. It was washed with deionized water until neutral, and then the solid and liquid were separated. The solid product was dried at 110°C for 10 hours to obtain a ZSM-5 molecular sieve encapsulated structure of precious metal catalyst masterbatch, marked as Pd x Mg y (NO3) z / ZSM-5.

[0051] 5. Pour 100 ml of deionized water into a stirring tank, add 16 g of TiO2, 12 g of CeO2, 4 g of La2O3, and 7.5 g of silica sol, mix well, stir-grind for 10 hours, and add Pd x Mg y (NO3) z / ZSM-5 masterbatch, pH regulator oxalic acid, continue stirring-grinding cycle for 4h, adjust the slurry pH to 5.2, and obtain honeycomb catalyst coating slurry; impregnate the coating slurry and apply it on a glass fiber carrier with specifications of 100*100*50 and 200 mesh, vacuum remove excess slurry, and then carry out hot air drying at 145°C and calcination at 500°C under nitrogen protection to obtain a molecular sieve encapsulated structure Pd-based honeycomb catalyst for anti-pollution flashover coating exhaust gas treatment (the mass ratio of precious metal to honeycomb catalyst is 0.5%).

[0052] Comparative Example

[0053] 60 ml of deionized water was measured and poured into a stirring tank. At the same time, 5 g of TiO2, 4.2 g of CeO2, 0.8 g of La2O3 and 3 g of silica sol were added and mixed evenly. The stirring-grinding cycle was completed for 10 hours. Then, 20 g of a 10% Pt(NO3)2 solution was added dropwise to the slurry. TEAOH was used as a pH regulator. The stirring-grinding cycle was continued for 4 hours. The pH of the slurry was adjusted to 6.3 to obtain a honeycomb catalyst coating slurry. The coating slurry was impregnated and coated on a cordierite honeycomb carrier with a specification of 100*100*50 and 200 mesh. The excess slurry was vacuumed off, and then hot air dried at 145°C and calcined at 500°C under nitrogen protection to obtain a conventional Pt-based honeycomb catalyst (the precious metal accounts for 0.6% of the mass of the entire honeycomb catalyst).

[0054] Characterization and performance testing

[0055] The catalysts prepared in Examples 1-3 were characterized by XRD. Figure 1 As shown, it can be seen that the XRD patterns of the three samples are consistent with the MFI topological structure, and the diffraction peak intensity is high, indicating good crystallinity. At the same time, no diffraction peak of precious metal oxides is found, indicating that the precious metals are in the pores of the ZSM-5 molecular sieve.

[0056] The honeycomb catalysts prepared in Examples 1-3 and the comparative example are cut into small cylinders of φ20*50, and loaded into the reactor of the catalyst performance evaluation device to carry out the catalytic oxidation reaction of VOCs in the anti-pollution flashover coating. The catalyst evaluation device is equipped with a multi-channel VOCs generator. The prepared anti-pollution flashover coating is atomized and volatilized by the VOCs generator. The exhaust gas contains VOCs such as xylene, dimethylsilane, and trichloroethylene. One channel of the VOCs generator is loaded with the prepared anti-pollution flashover coating, and the concentration of volatiles is adjusted to 500ppm. Another channel is introduced with SO2 gas, and the concentration is set to 50ppm. Another channel is introduced with compressed air of a set flow rate, and the air velocity is set to 15000h -1 The reaction tail gas was tested for outlet concentration by PID detector, and the reaction was continued for 60 hours. The reaction temperature at 95% conversion rate was recorded every hour and recorded as T95 The reaction results are shown in Table 1.

[0057] It can be seen from the data in Table 1 that in the first hour of the reaction, the catalytic temperatures of Examples 1-3 and the comparative example are between 200-250°C, and the [HOCH2CH2NH3]2Pt(OH)6 active component used in Example 2 exhibits a lower catalytic temperature and higher activity; after 60 hours of continuous reaction, the performance has a certain degree of attenuation, and the T of Examples 1-3 is 95 The reaction temperature increased by 15-20°C, while the comparative example showed a greater attenuation, T 95 It increased by 55°C, which shows that Examples 1-3 have good catalytic activity against silane and halogen in anti-fouling flashover coatings, and have certain anti-sulfur performance. It is speculated that the possible reason is that the presence of B acid sites in ZSM-5 inhibits the surface adsorption of SO2. Isolating the contact between toxic substances and active metals is an important strategy to slow down the rate of catalyst poisoning.

[0058] Table 1:

[0059] project T95 (1st hour) T95 (60th hour) Example 1 230 250 Example 2 210 225 Example 3 240 260 Comparative Example 220 275

Claims

1. A method for preparing a ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst, characterized in that: The following steps are involved: S1. Preparation of all-silicon ZSM-5 precursor: dissolve the alkali source in deionized water and stir until fully dissolved to form an alkaline solution; add the silicon source to the alkaline solution, mix and stir for 1-4 hours to form a silicate gel, and let it stand in a water bath at 60-90°C for 1-4 hours to obtain an all-silicon ZSM-5 molecular sieve precursor solution; wherein the molar ratio of SiO2 in the silica sol to OH- in the alkali is 1:(60-80); S2. Preparation of precious metal complexes: dissolving alkaline earth metal salt and precious metal salt in deionized water, adding complexing agent, stirring evenly, and heating in a water bath to obtain a precious metal complex solution; wherein the mass ratio of precious metal: alkaline earth metal: complexing agent is 1:(2-5):(0.1-1), the water bath temperature is 60-80°C, and the water bath time is 2-4h; S3, preparation of molecular sieve seed crystals loaded with precious metal complexes; taking a certain amount of template solution; simultaneously dropping the precious metal complex solution and template solution in S2 into the gel of S1, controlling the dropping speed to avoid local reaction; then reflux in an oil bath at 80-160°C for 6-24h to form a ZSM-5 molecular sieve seed crystal colloid wrapped with precious metal complexes; wherein the mass ratio of precious metal complex to template is 1:(0.1-1); S4, preparation of ZSM-5 molecular sieve encapsulated Pt or Pd complex masterbatch; the colloid obtained in S3 is transferred to a high-pressure reactor, the reactor is tightened, and placed in an oven, the reaction temperature is set to 100-200°C, and crystallization and nucleation are carried out at a constant temperature for 7-14 days. After the nucleation is completed, it is cooled to room temperature, the kettle is opened for filtration, and the product is washed with deionized water until neutral, and solid-liquid separation is performed to obtain a solid product; the solid product is dried at 80-150°C for 4-8 hours to obtain a precious metal catalyst masterbatch with a ZSM-5 molecular sieve encapsulation structure, which is marked as PM / ZSM-5; S5. Preparation of honeycomb catalyst coating: adding metal oxide, rare earth oxide, deionized water and binder into a stirring tank, blending, stirring and grinding to prepare nano-scale coating slurry, wherein the mass fractions of each component are 10-30 parts of metal oxide, 10-30 parts of rare earth oxide, 100 parts of deionized water and 1-5 parts of binder; adding 1-10 parts of PM / ZSM-5 and 0.1-1 parts of additives into the slurry, blending and stirring for 1-4 hours and grinding for 1-4 hours at room temperature, and adjusting the pH range of the system to 3.5-6.5; S6, preparation of honeycomb catalyst; coating the slurry obtained in S5 on a honeycomb carrier, vacuuming away excess slurry, drying with hot air at 60-150°C, and calcining at 400-600°C under nitrogen protection to obtain a molecular sieve encapsulated precious metal honeycomb catalyst for the treatment of anti-pollution flashover coating exhaust gas.

2. The method for preparing the ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst according to claim 1, characterized in that: The alkali source described in S1 is at least one of NaOH and KOH; the silicon source is at least one of silica sol, tetraethyl orthosilicate, white carbon black and water glass.

3. The method for preparing the ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst according to claim 1, characterized in that: S2 The noble metal salt described in the method is at least one of platinum nitrate Pt(NO3)2, di(ethanolammonium)hexahydroxyplatinate [HOCH2CH2NH3]2Pt(OH)6, and palladium nitrate Pd(NO3)2.

4. The method for preparing the ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst according to claim 1, characterized in that: S2 The alkaline earth metal salt is at least one of acetate and nitrate of magnesium, calcium, strontium and barium salts; the complexing agent is at least one of polyvinyl alcohol (PVA), ethylenediaminetetraacetic acid (EDTA) and polyethylene glycol (PEG).

5. The method for preparing the ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst according to claim 1, characterized in that: S3 The template agent is at least one substance selected from tetraethylammonium hydroxide TEAOH, tetrapropylammonium hydroxide TPAOH, tetrapropylammonium bromide TEAB, ethylenediamine EDA and n-butylamine solution with a mass concentration of 10% to 50%.

6. The method for preparing the ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst according to claim 1, characterized in that: The metal oxide is at least one of Al2O3, TiO2, and ZrO2; the rare earth oxide is at least one of CeO2, La2O3, and Y2O3; and the binder is at least one of silica sol and alumina sol.

7. The method for preparing the ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst according to claim 1, characterized in that: S5 The auxiliary agents described in the invention include dispersants, pH regulators, and defoamers; the dispersants include one or a mixture of ultrafine barium sulfate and titanium dioxide; the pH regulators include alkali regulators and acid regulators, the alkali regulator is at least one of TEAOH, EDA, and Ba(OH)2, and the added amount accounts for 0.01% to 5% of the total amount of the coating slurry; the acid regulator is at least one of citric acid, oxalic acid, and dilute nitric acid, and the added amount accounts for 0.01% to 5% of the total amount of the coating slurry; the defoamer is at least one of silicone oil, sodium polyether sulfate, and sodium dodecylbenzene sulfonate, and the added amount accounts for 0.01% to 5% of the total amount of the coating slurry.

8. The method for preparing the ZSM-5 molecular sieve encapsulated precious metal honeycomb catalyst according to claim 1, characterized in that: The honeycomb carrier in S6 is a cordierite honeycomb ceramic carrier, a glass fiber corrugated honeycomb carrier, or a metal wire mesh honeycomb carrier, with a mesh number of 60-600.

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