Bifunctional membrane for NH3-SCR (selective catalytic reduction) and particulate matter filtration and preparation method of bifunctional membrane

Abstract

The invention discloses a bifunctional membrane for NH3-SCR (Selective Catalytic Reduction) denitration and particulate matter filtration and a preparation method of the bifunctional membrane. The preparation method comprises the following steps: firstly, carrying out surface modification on a Cu-SSZ-13 molecular sieve by utilizing a silane coupling agent to obtain a modified molecular sieve CS-K5, and then stably loading the CS-K5 on the surface of the fiber by utilizing an in-situ covalent bonding technology by taking electrostatic spinning polyimide fiber as a carrier to form a bifunctional membrane material with a molecular sieve-silane-polymer ternary interface structure. The obtained bifunctional film is kept at 1t; according to the present invention, the denitration rate at the low temperature of 225 DEG C is not less than 99% while the low pressure drop of 1000 Pa is achieved, the PM 0.3 interception rate is not less than 80%, and the catalyst has advantages of excellent cycle stability, excellent water vapor resistance and excellent sulfur resistance. According to the bifunctional membrane, through the dual mechanisms of Lewis acid reinforcement and fiber network mass transfer optimization, the synergistic enhancement of catalysis and filtration functions is realized, and the bifunctional membrane is suitable for the synergistic purification scene of multiple pollutants such as industrial flue gas and diesel tail gas.

Description

Technical Field

[0001] This invention belongs to the technical field of industrial waste gas purification materials, specifically relating to a bifunctional membrane for NH3-SCR and particulate matter filtration and its preparation method. Background Technology

[0002] industrial emissions of nitrogen oxides (NOx) x NO and particulate matter (PM) are two major air pollutants. x It can cause severe air pollution phenomena such as acid rain and smog, and PM has been proven to cause irreversible physiological damage to the human body. Modern exhaust gas treatment systems mainly use multi-stage sequential processes to reduce pollutants. Upstream, PM pollutants are captured and removed through filtration, and then in the downstream denitrification unit, NH3 selective catalytic reduction (NH3-SCR) technology is used to remove NO from the gas. x It is converted into harmless N2 and H2O. However, traditional separation and processing methods suffer from drawbacks such as high operating costs, large space requirements, and complex processes. Therefore, developing bifunctional materials that integrate catalysis and separation functions has become a promising solution to this challenge.

[0003] For bifunctional materials that integrate catalysis and separation, the goal is to simultaneously capture solid and gaseous pollutants in a single unit operation by combining chemical catalysis and physical filtration. To achieve this, bifunctional membrane engineering has become a key approach to improving PM and NO separation. x The breakthrough technology of synergistic removal efficiency has led to widespread attention on the preparation of bifunctional membranes. Highly efficient bifunctional membrane materials must simultaneously possess the following three properties: [specific properties not specified in the original text]. x Excellent removal efficiency, strong adhesion between catalyst and substrate, and constraints in operating pressure drop. Currently, bifunctional membrane materials are typically composed of a functionalized material substrate and a catalytically active component. The mainstream substrate types and their characteristics are as follows: Metal mesh and honeycomb structure substrates were early types developed to reduce gas flow pressure drop. Although they can reduce gas flow resistance through their regular channel structure, they are limited by their small specific surface area and limited catalyst loading, leading to NO removal efficiency issues. xThe catalytic efficiency is low, which is difficult to meet the deep denitration demand under the new emission standard; and the fiber-based substrate has become the mainstream direction of the current substrate research due to the high specific surface area (which can improve the catalyst loading) and high porosity (which can reduce the airflow pressure drop) brought by the three-dimensional network structure, wherein the electrospun fiber substrate has excellent specific surface area and interconnected pore structure, which can effectively balance the PM interception efficiency and filtration resistance, and its mature preparation process has been verified in the fields of catalytic carrier, optoelectronics, etc., and has industrial application potential; the ceramic fiber substrate has excellent chemical stability and good compatibility with the subsequent commonly used molecular sieve catalyst, but it is inherently brittle and easy to break under industrial airflow impact, which is difficult to meet the mechanical stability requirements for long-term operation; the polymer fiber substrate has good mechanical flexibility, which can solve the brittleness problem of ceramic fibers, but due to the strong chemical inertness, the interface adhesion with the catalyst (especially the molecular sieve) is poor, which is easy to cause the catalyst to fall off, resulting in reduced catalytic performance.

[0004] On the other hand, the catalytically active component needs to have high NH3-SCR activity (especially low-temperature activity), wide denitration temperature window and good hydrothermal stability, and needs to be efficiently integrated with the substrate material. So far, although the traditional catalyst has certain denitration activity, it is easy to cause particle agglomeration when directly loaded on the substrate, which leads to reduced accessibility of active sites, large mass transfer resistance, and low-temperature denitration efficiency that is difficult to meet industrial requirements. It should be noted that the molecular sieve catalyst can realize uniform dispersion of active metals due to its high specific surface area and unique pore structure, thereby exhibiting more excellent denitration performance. Among them, Cu-SSZ-13 molecular sieve has become the most potential NH3-SCR catalyst due to its wide denitration temperature window of 200-550 °C and excellent hydrothermal stability. However, this type of molecular sieve has problems such as strict synthesis process requirements, sensitivity of the crystallization process to the reaction environment (temperature, pH, precursor concentration), and difficulty in realizing in-situ growth or uniform loading on different types of substrates (especially fiber substrates). The existing dual-function film material preparation scheme is mostly to combine Cu-SSZ-13 with SiC material (SiC has high chemical stability and can adapt to molecular sieve synthesis), but the inherent dense structure of SiC material leads to low porosity, which makes the overall pressure drop of the catalytic membrane far exceed the threshold value (1000 Pa) required by industry, and cannot meet the requirements of high denitration activity and low pressure drop.

[0005] In summary, the high-efficiency molecular sieve catalyst such as Cu-SSZ-13 is difficult to be efficiently integrated with the substrate, and the existing integration scheme will sacrifice the low pressure drop advantage of the substrate. Therefore, the current problems faced by the functional material substrate and the catalytically active component are the contradiction between high denitration performance and substrate integration, low pressure drop requirements, which leads to the fact that the dual-function film material cannot meet the dual requirements of "high denitration efficiency" and "industrial low pressure drop" at the same time. SUMMARY

[0006] The present application aims to overcome the deficiencies of the prior art and provide a bifunctional membrane for NH3-SCR and particulate filtration and a preparation method thereof, which has the characteristics of high low-temperature denitration activity, low pressure drop, high filtration efficiency and excellent stability.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A bifunctional membrane for NH3-SCR and particulate filtration comprises a polyimide electrospun fiber carrier and a Cu-SSZ-13 molecular sieve catalyst covalently grafted on the surface thereof through a silane coupling agent KH550, forming a ternary interface structure of "molecular sieve-silane bridge-fiber", and a preparation method thereof comprises the following steps: (1) Surface modification of Cu-SSZ-13 molecular sieve catalyst and silane coupling agent in an ethanol-water mixed solution to obtain modified molecular sieve catalyst CS-K5; (2) Preparation of polyamic acid (PAA) solution as spinning solution, and spinning of PAA solution into PAA fiber membrane by electrospinning; (3) Loading of the modified molecular sieve catalyst CS-K5 on the PAA fiber membrane to obtain CS-K5-PAA precursor membrane; (4) Stepwise temperature rising heat treatment of the CS-K5-PAA precursor membrane to obtain a bifunctional membrane of polyimide loaded Cu-SSZ-13 (CS-K5-PI).

[0008] Further, the preparation method of the Cu-SSZ-13 molecular sieve catalyst in step (1) is as follows: H-type FAU molecular sieve, Al(OH)3 and N,N,N-trimethyl-1-adamantylammonium hydroxide (TMAdaOH) are used as raw materials, a synthesis gel is prepared according to the molar ratio of 1 SiO2:0.05 Al2O3:5 H2O:0.4 TMAdaOH, hydrothermal crystallization is carried out at 155-165 °C for 90-100 h, and H-SSZ-13 is obtained after washing, drying and calcination, the H-SSZ-13 is added to a Cu(NO3)2 solution for ion exchange and calcination to obtain the Cu-SSZ-13 molecular sieve catalyst.

[0009] Further, the surface modification method in step (1) is as follows: an ethanol-water mixed solution with a volume ratio of ethanol to water of 18-20:1 is adjusted to a pH of 8-9, 1-5 wt% of silane coupling agent KH550 and 10 wt% of Cu-SSZ-13 molecular sieve catalyst are added, ultrasonic treatment is carried out for 5-10 min, stirring reaction is carried out at 60-90 °C for 2.8-3.2 h, the liquid is completely evaporated, and then washed and dried to obtain the modified molecular sieve catalyst CS-K5.

[0010] Further, the PAA solution described in step (2) is prepared by using 4,4'-diaminodiphenyl ether (ODA) and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) as monomers, with a monomer addition molar ratio of n(ODA):n(BPDA)=1:1.01, and polymerizing in DMF solvent for 5.5-6.5 h to obtain a 20-30 wt% PAA solution.

[0011] Further, the electrospinning parameters in step (2) include: voltage 19-20 kV, receiver rotation speed 180-220 r / min, feed speed 0.45-0.55 mL / h, needle tip to receiver distance 13-15 cm, oscillation amplitude 25-26 cm, oscillation speed 2.3-2.5 mm / s, temperature 25±5 °C, and humidity 40±5%.

[0012] Further, step (3) is as follows: the modified molecular sieve catalyst CS-K5 is dispersed in ethanol, sonicated for 0.8-1.2 h, and stirred for 0.4-0.6 h to obtain a suspension with a CS-K5 content of 52-73 wt%. Then, the PAA fiber membrane is immersed in the suspension and stirred for 5.5-6.5 h to load the modified molecular sieve catalyst CS-K5 onto the PAA fiber membrane. Finally, it is washed and dried to obtain the CS-K5-PAA precursor membrane.

[0013] Further, the heat treatment procedure in step (4) includes: heating to 140-160 °C at a rate of 1.8-2.2 °C / min and holding for 25-35 min; continuing to heat to 240-260 °C and holding for 25-35 min; then heating to 290-310 °C and holding for 1.8-2.2 h, and then naturally cooling to room temperature.

[0014] Furthermore, the molecular sieve loading in the resulting bifunctional membrane is 48-61 wt%.

[0015] This invention also provides the application of the above-mentioned bifunctional membrane in NH3-SCR and particulate matter filtration, which can be used in the fields of industrial flue gas and diesel exhaust gas purification.

[0016] Furthermore, when the bifunctional membrane is used for NH3-SCR and particulate matter filtration, NO at 225 °C... x The conversion rate is no less than 99%, and the PM0.3 interception rate is no less than 80%.

[0017] This invention first modifies the surface of Cu-SSZ-13 molecular sieve using a silane coupling agent to obtain a modified molecular sieve CS-K5. Then, using electrospun polyimide (PI) fibers as a carrier, CS-K5 is stably loaded onto the fiber surface using in-situ covalent bonding technology, forming a bifunctional membrane material with a "molecular sieve-silane-polymer" ternary interface structure that integrates NH3-SCR denitrification and particulate matter filtration functions. Compared with existing technologies, this invention has the following advantages: (1) This invention establishes a stable covalent bonding interface of "molecular sieve-Si-O-Si-silane-NH-CO-polymer" through a two-stage reaction mechanism of "in-situ hydrolysis condensation-nucleophilic acylation", which realizes a strong interfacial bond and significantly improves the stability of bifunctional membranes.

[0018] (2) The three-dimensional network structure of the fibrous bifunctional membrane prepared in this invention significantly improves mass transfer efficiency through the following mechanisms: i) increasing the gas-solid contact area; ii) optimizing the flow field distribution and reducing flow dead zones; iii) disrupting the laminar boundary layer and reducing mass transfer resistance. Under the same pressure drop, the average gas velocity in the fibrous bifunctional membrane is significantly higher than that of the particulate catalyst. This allows the bifunctional membrane to maintain excellent catalytic performance under high space velocity conditions, and the reaction rate is much higher than that of the particulate catalyst, greatly improving the waste gas treatment capacity of the reactor.

[0019] (3) The present invention enhances the mechanical strength of the fiber membrane by introducing molecular sieve, enabling it to withstand various external forces during the filtration process, and keeping the denitrification performance and filtration efficiency of the catalytic membrane stable.

[0020] (4) This invention utilizes the silane coupling agent KH550 to modify the surface of Cu-SSZ-13 molecular sieve, successfully inducing the reconstruction of copper species on the molecular sieve surface. This structural change significantly increases the number of Lewis acid sites on the catalyst surface, enriches the types and quantities of nitrate intermediates, optimizes the NH3-SCR reaction pathway, and can improve its low-temperature denitrification performance.

[0021] (5) The unique "fiber-molecular sieve" composite structure proposed in this invention creates a multi-stage filtration mechanism: i) the three-dimensional fiber network provides efficient physical interception; ii) the surface-loaded nanoscale molecular sieve particles significantly increase the surface roughness of the fibers, enhancing the adsorption and capture of ultrafine particles through van der Waals forces and electrostatic interactions; iii) the microporous structure of the molecular sieve itself provides a confined filtration effect. The synergistic effect of these three factors enables the catalytic membrane to achieve an interception rate of over 99.99% for PM0.3, meeting stringent ultra-low emission requirements.

[0022] (6) By precisely optimizing the molecular sieve addition amount and precursor polymer concentration, the present invention achieves bidirectional precise control of molecular sieve loading and fiber size; and finally determines the optimal parameter combination so that the catalytic activity of the catalyst and the structural advantages of the fiber substrate can be deeply synergistic, significantly improving the overall denitrification performance and achieving a synergistic effect of "1+1>2".

[0023] (7) The polyimide fiber network constructed by electrospinning technology in this invention has high porosity and excellent permeability. While ensuring high filtration efficiency, it maintains the operating pressure drop below 1000 Pa, which is far lower than the pressure drop level of traditional ceramic catalytic membranes (usually greater than 1000 Pa). This low-resistance characteristic can significantly reduce the energy consumption of the induced draft fan and reduce the system operating cost.

[0024] (8) The inherent hydrophobicity of the polyimide matrix and the hydrophilicity after molecular sieve modification are well balanced, effectively inhibiting the competitive adsorption of water molecules at the active site, giving the bifunctional membrane excellent hydrothermal stability and resistance to water vapor and sulfur poisoning, making it suitable for the complex composition of actual industrial flue gas.

[0025] (9) This invention successfully integrates catalytic and filtration functions into a single material, achieving simultaneous NO removal in a single unit operation. x PM can replace the traditional two-stage treatment system of "SCR reactor + bag filter", greatly simplifying the process and reducing equipment footprint and initial investment. The entire preparation process requires no special equipment, the raw materials are readily available, the operating conditions are mild, and it is suitable for large-scale continuous production. Attached Figure Description

[0026] Figure 1 The images are scanning electron microscope (SEM) images of the samples prepared in Examples 1-4 and Comparative Examples 1-3.

[0027] Figure 2 The diagram shows a comparison of the denitrification performance of the samples prepared in Examples 1-4 and Comparative Examples 1-3.

[0028] Figure 3 The graph shows a comparison of the filtration performance of the samples prepared in Examples 1-4 and Comparative Examples 1-3.

[0029] Figure 4 The results are as follows: stability test results of the sample prepared in Example 1; a) Monitoring curve after continuous operation at 225 °C for 250 h; b) Monitoring data of quartz crystal microbalance (QCM).

[0030] Figure 5 The images show SEM images of the sample prepared in Example 1 before and after cleaning.

[0031] Figure 6The results are the water resistance test results of the samples prepared in Example 1 and Comparative Example 1.

[0032] Figure 7 The results are the sulfur resistance test results of the sample prepared in Example 1. Detailed Implementation

[0033] To facilitate understanding of the present invention, the technical solutions described below are further illustrated with specific embodiments, but the present invention is not limited thereto. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in the present invention can be purchased commercially or prepared using existing methods. Example 1

[0034] A method for preparing a bifunctional membrane for NH3-SCR and particulate filtration includes the following steps: (1) Preparation of Cu-SSZ-13 molecular sieve catalyst 3.13 g of HY molecular sieve (Si / Al=20), 0.195 g of Al(OH)3 and 16.885 g of TMAdaOH aqueous solution (25 wt%) were mixed evenly, and 8.170 g of water was evaporated by stirring at 80 °C. The resulting gel was transferred to a stainless steel reactor lined with polytetrafluoroethylene and statically crystallized at 160 °C for 4 days. After crystallization, the product was centrifuged, washed with deionized water, dried at 100 °C for 12 h, and then calcined at 600 °C for 6 h to obtain H-type SSZ-13 molecular sieve.

[0035] 1.0 g of the above-mentioned H-type SSZ-13 molecular sieve was mixed with 50 mL of 0.1 mol / L Cu(NO3)2 aqueous solution and subjected to ion exchange at 80°C for 4 h. This process was repeated three times to ensure complete exchange. After washing and drying, the exchanged product was calcined at 550°C for 6 h to obtain the Cu-SSZ-13 catalyst.

[0036] (2) Preparation of modified molecular sieve catalyst CS-K5 Take 8 g of a mixed solvent of ethanol and water (volume ratio 19:1) and adjust the pH to 8.5 with ammonia. Add 0.01 g of KH550 and stir to ensure complete hydrolysis. Add 1.0 g of the Cu-SSZ-13 catalyst prepared above and sonicate for 5 min to ensure uniform dispersion. Place the mixture in an 80 °C water bath and stir under closed conditions (300 rpm) for 3 h. Then open the container lid and evaporate to dryness at 80 °C. Add 8.0 g of fresh ethanol / water (19:1) mixed solvent to the dried solid and stir under closed conditions for 1 h to dissolve unreacted KH550. Finally, remove the physically adsorbed coupling agent by centrifugation and multiple washings with ethanol. Dry the resulting solid at 100 °C for 12 h to obtain the silanized modified molecular sieve CS-K5.

[0037] (3) Preparation of PAA fiber membrane In a three-necked flask containing 15 g DMF, add 2.01 g ODA and stir mechanically until completely dissolved. Add 2.99 g BPDA in three slow batches, maintaining an ODA:BPDA ratio of 1:1.01. Stir until completely dissolved after each addition, with intervals of approximately 30 min. After all additions are complete, continue rapid stirring for 6 h to obtain a pale yellow, viscous 25 wt% PAA solution. Allow to stand for 12 h to remove bubbles before use.

[0038] The PAA solution was loaded into a syringe for electrospinning. The main parameters were set as follows: voltage 19.5 kV, feed rate 0.5 mL / h, receiver distance 14 cm, receiver rotation speed 200 r / min, oscillation amplitude 25.5 cm, and oscillation speed 2.4 mm / s. The ambient temperature was controlled at 25±5 °C, and the humidity at 40±5%. Oiled paper was placed over the receiver to collect a uniform PAA fiber membrane.

[0039] (4) CS-K5 was loaded onto PAA fiber membrane to prepare CS-K5-PAA precursor membrane. Weigh 0.4 g of CS-K5 molecular sieve and disperse it in 1 L of ethanol. Sonicate for 1 h, then mechanically stir for 0.5 h to form a stable suspension. Fix the prepared PAA fiber membrane (13 cm × 22 cm) onto a self-made roller device and vertically immerse it in the suspension. Turn on the cantilever stirrer and stir at 100 rpm at room temperature for 6 h to ensure the molecular sieve is fully loaded onto the fibers. After removing the membrane, wash it with ethanol for 30 min to remove the physically adsorbed molecular sieve from the surface, and dry it at 35 °C for 0.5 h to obtain the CS-K5-PAA precursor membrane.

[0040] (5) Preparation of bifunctional membranes The CS-K5-PAA precursor membrane was placed in a muffle furnace and subjected to step heat treatment in air: the temperature was increased to 150 °C at a rate of 2 °C / min and held for 30 min; then increased to 250 °C and held for 30 min; finally, the temperature was increased to 300 °C and held for 2 h. After the process was completed, it was allowed to cool naturally to room temperature to obtain the final polyimide-based catalytic membrane (bifunctional membrane). The actual molecular sieve loading was calculated to be 61 wt%, hence the name 61CS-K5-PI.

[0041] The denitrification performance of the fabricated bifunctional membrane was tested in a fixed-bed reactor. The reaction temperature was 100-300 °C. Catalyst evaluation conditions: 500 ppm NO, 500 ppm NH3, 8 v% O2, N2 as equilibrium gas, and a volume hourly space velocity (GHSV) of 60,000 h⁻¹. -1 The total gas flow rate was 200 ml / min. During the reaction evaluation, the denitrification rate of 61CS-K5-PI at 225 °C was recorded as 100% using a gas analyzer (Testo®340).

[0042] The filtration efficiency and pressure drop of the fabricated dual-function membrane were tested using an LZC-K1 filter media performance tester manufactured by Suzhou Huada Equipment Co., Ltd. The aerosol generator continuously generated approximately 450,000 particles. The specific test method for dust removal performance was in accordance with the "Technical Requirements for Bag Filters" (GB / T 6719-2009). The filtration velocity was 1.0 m / min. The test results were as follows: the PM0.3 filtration efficiency of 61CS-K5-PI was 99.99%, and the pressure drop was 602.5 Pa. Example 2

[0043] A method for preparing a bifunctional membrane for NH3-SCR and particulate filtration includes the following steps: (1) Preparation of Cu-SSZ-13 molecular sieve catalyst 3.13 g of HY molecular sieve (Si / Al=20), 0.195 g of Al(OH)3 and 16.885 g of TMAdaOH aqueous solution (25 wt%) were mixed evenly, and 8.170 g of water was evaporated by stirring at 80 °C. The resulting gel was transferred to a stainless steel reactor lined with polytetrafluoroethylene and statically crystallized at 160 °C for 4 days. After crystallization, the product was centrifuged, washed with deionized water, dried at 100 °C for 12 h, and then calcined at 600 °C for 6 h to obtain H-type SSZ-13 molecular sieve.

[0044] 1.0 g of the above-mentioned H-type SSZ-13 molecular sieve was mixed with 50 mL of 0.1 mol / L Cu(NO3)2 aqueous solution and subjected to ion exchange at 80°C for 4 h. This process was repeated three times to ensure complete exchange. After washing and drying, the exchanged product was calcined at 550°C for 6 h to obtain the Cu-SSZ-13 catalyst.

[0045] (2) Preparation of modified molecular sieve catalyst CS-K5 Take 8.0 g of a mixed solvent of ethanol and water (volume ratio 19:1) and adjust the pH to 8.5 with ammonia. Add 0.05 g of KH550 and stir to ensure complete hydrolysis. Add 1.0 g of the Cu-SSZ-13 catalyst prepared above and sonicate for 5 min to ensure uniform dispersion. Place the mixture in a 60 °C water bath and stir under closed conditions (300 rpm) for 3 h. Then open the container lid and evaporate to dryness at 80 °C. Add 8.0 g of fresh ethanol / water (19:1) mixed solvent to the dried solid and stir under closed conditions for 1 h to dissolve unreacted KH550. Finally, remove the physically adsorbed coupling agent by centrifugation and repeated washing with ethanol. Dry the resulting solid at 100 °C for 12 h to obtain the silanized modified molecular sieve catalyst CS-K5.

[0046] (3) Preparation of PAA fiber membrane In a three-necked flask containing 15 g DMF, add 1.91 g ODA and stir mechanically until completely dissolved. Add 2.83 g BPDA in three slow batches, maintaining an ODA:BPDA ratio of 1:1.01. Stir until completely dissolved after each addition, with intervals of approximately 30 min. After all additions are complete, continue rapid stirring for 6 h to obtain a pale yellow, viscous 24 wt% PAA solution. Allow to stand for 12 h to remove bubbles before use.

[0047] The PAA solution was loaded into a syringe for electrospinning. The main parameters were set as follows: voltage 19.5 kV, feed rate 0.5 mL / h, receiver distance 14 cm, receiver rotation speed 200 r / min, oscillation amplitude 25.5 cm, and oscillation speed 2.4 mm / s. The ambient temperature was controlled at 25±5 °C, and the humidity at 40±5%. Oiled paper was placed over the receiver to collect a uniform PAA fiber membrane.

[0048] (4) CS-K5 was loaded onto PAA fiber membrane to prepare CS-K5-PAA precursor membrane. Weigh 0.2 g of CS-K5 molecular sieve and disperse it in 1 L of ethanol. Sonicate for 1 h, then mechanically stir for 0.5 h to form a stable suspension. Fix the prepared PAA fiber membrane (13 cm × 22 cm) onto a self-made roller device and vertically immerse it in the suspension. Turn on the cantilever stirrer and stir at 100 rpm at room temperature for 6 h to ensure the molecular sieve is fully loaded onto the fibers. After removing the membrane, wash it with ethanol for 30 min to remove the physically adsorbed molecular sieve from the surface, and dry it at 35 °C for 0.5 h to obtain the CS-K5-PAA precursor membrane.

[0049] The CS-K5-PAA precursor membrane was placed in a muffle furnace and subjected to step heat treatment in air: the temperature was increased to 150 °C at a rate of 2 °C / min and held for 30 min; then increased to 250 °C and held for 30 min; finally, the temperature was increased to 300 °C and held for 2 h. After the process was completed, it was allowed to cool naturally to room temperature to obtain the final polyimide-based catalytic membrane (bifunctional membrane). The actual molecular sieve loading was calculated to be 48 wt%, hence the name 48CS-K5-PI.

[0050] The denitrification performance of the fabricated bifunctional membrane was tested in a fixed-bed reactor. The reaction temperature was 100-300 °C. Catalyst evaluation conditions: 500 ppm NO, 500 ppm NH3, 8 v% O2, N2 as equilibrium gas, GHSV for 60,000 h⁻¹. -1 The total gas flow rate was 200 ml / min. During the reaction evaluation, the denitrification rate of 48CS-K5-PI at 225 °C was recorded as 100% using a gas analyzer (Testo®340).

[0051] The filtration efficiency and pressure drop of the dual-function membrane were tested using an LZC-K1 filter media performance tester manufactured by Suzhou Huada Equipment Co., Ltd. The aerosol generator continuously generated approximately 450,000 particles. The specific test method for dust removal performance was in accordance with the "Technical Requirements for Bag Filters" (GB / T 6719-2009). The filtration velocity was 1.0 m / min. The test results were as follows: the PM0.3 filtration efficiency of 48CS-K5-PI was 81.32%, and the pressure drop was 346.2 Pa. Example 3

[0052] A method for preparing a bifunctional membrane for NH3-SCR and particulate filtration includes the following steps: (1) Preparation of Cu-SSZ-13 molecular sieve catalyst 3.13 g of HY molecular sieve (Si / Al=20), 0.195 g of Al(OH)3 and 16.885 g of TMAdaOH aqueous solution (25 wt%) were mixed evenly, and 8.170 g of water was evaporated by stirring at 80 °C. The resulting gel was transferred to a stainless steel reactor lined with polytetrafluoroethylene and statically crystallized at 160 °C for 4 days. After crystallization, the product was centrifuged, washed with deionized water, dried at 100 °C for 12 h, and then calcined at 600 °C for 6 h to obtain H-type SSZ-13 molecular sieve.

[0053] 1.0 g of the above-mentioned H-type SSZ-13 molecular sieve was mixed with 50 mL of 0.1 mol / L Cu(NO3)2 aqueous solution and subjected to ion exchange at 80°C for 4 h. This process was repeated three times to ensure complete exchange. After washing and drying, the exchanged product was calcined at 550°C for 6 h to obtain the Cu-SSZ-13 catalyst.

[0054] (2) Preparation of modified molecular sieve catalyst CS-K5 Take 8.0 g of a mixed solvent of ethanol and water (volume ratio 19:1) and adjust the pH to 8.5 with ammonia. Add 0.02 g of KH550 and stir to ensure complete hydrolysis. Add 1.0 g of the Cu-SSZ-13 catalyst prepared above and sonicate for 5 min to ensure uniform dispersion. Place the mixture in a 70 °C water bath and stir under closed conditions (300 rpm) for 3 h. Then open the container lid and evaporate to dryness at 80 °C. Add 8.0 g of fresh ethanol / water (19:1) mixed solvent to the dried solid and stir under closed conditions for 1 h to dissolve unreacted KH550. Finally, remove the physically adsorbed coupling agent by centrifugation and repeated washing with ethanol. Dry the resulting solid at 100 °C for 12 h to obtain the silanized modified molecular sieve catalyst CS-K5.

[0055] (3) Preparation of PAA fiber membrane In a three-necked flask containing 15 g DMF, add 2.12 g ODA and stir mechanically until completely dissolved. Add 3.15 g BPDA in three slow batches, maintaining an ODA:BPDA ratio of 1:1.01. Stir until completely dissolved after each addition, with approximately 30 min intervals between batches. After all additions are complete, continue rapid stirring for 6 h to obtain a pale yellow, viscous 26 wt% PAA solution. Allow to stand for 12 h to remove bubbles before use.

[0056] The PAA solution was loaded into a syringe for electrospinning. The main parameters were set as follows: voltage 19.5 kV, feed rate 0.5 mL / h, receiver distance 14 cm, receiver rotation speed 200 r / min, oscillation amplitude 25.5 cm, and oscillation speed 2.4 mm / s. The ambient temperature was controlled at 25±5 °C, and the humidity at 40±5%. Oiled paper was placed over the receiver to collect a uniform PAA fiber membrane.

[0057] (4) CS-K5 was loaded onto PAA fiber membrane to prepare CS-K5-PAA precursor membrane. Weigh 0.3 g of CS-K5 molecular sieve and disperse it in 1 L of ethanol. Sonicate for 1 h, then mechanically stir for 0.5 h to form a stable suspension. Fix the prepared PAA fiber membrane (13 cm × 22 cm) onto a self-made roller device and vertically immerse it in the suspension. Turn on the cantilever stirrer and stir at 100 rpm at room temperature for 6 h to ensure the molecular sieve is fully loaded onto the fibers. After removing the membrane, wash it with ethanol for 30 min to remove the physically adsorbed molecular sieve from the surface, and dry it at 35 °C for 0.5 h to obtain the CS-K5-PAA precursor membrane.

[0058] (5) Preparation of bifunctional membranes The CS-K5-PAA precursor membrane was placed in a muffle furnace and subjected to step heat treatment in air: the temperature was increased to 150 °C at a rate of 2 °C / min and held for 30 min; then increased to 250 °C and held for 30 min; finally, the temperature was increased to 300 °C and held for 2 h. After the process was completed, it was allowed to cool naturally to room temperature to obtain the final polyimide-based catalytic membrane (bifunctional membrane). The actual molecular sieve loading was calculated to be 54 wt%, hence the name 54CS-K5-PI.

[0059] The denitrification performance of the fabricated bifunctional membrane was tested in a fixed-bed reactor. The reaction temperature was 100-300 °C. Catalyst evaluation conditions: 500 ppm NO, 500 ppm NH3, 8 v% O2, N2 as equilibrium gas, GHSV for 60,000 h⁻¹. -1 The total gas flow rate was 200 ml / min. During the reaction evaluation, the denitrification rate of 54CS-K5-PI at 225 °C was recorded as 100% using a gas analyzer (Testo®340).

[0060] The filtration efficiency and pressure drop of the dual-function membrane were tested using an LZC-K1 filter media performance tester manufactured by Suzhou Huada Equipment Co., Ltd. The aerosol generator continuously generated approximately 450,000 particles. The specific test method for dust removal performance was in accordance with the "Technical Requirements for Bag Filters" (GB / T 6719-2009). The filtration velocity was 1.0 m / min. The test results were as follows: the PM0.3 filtration efficiency of 54CS-K5-PI was 88.7%, and the pressure drop was 468.8 Pa. Example 4

[0061] A method for preparing a bifunctional membrane for NH3-SCR and particulate filtration includes the following steps: (1) Preparation of Cu-SSZ-13 molecular sieve catalyst 3.13 g of HY molecular sieve (Si / Al=20), 0.195 g of Al(OH)3, and 16.885 g of TMAdaOH aqueous solution (25 wt%) were mixed thoroughly, and 8.170 g of water was evaporated by stirring at 80 °C. The resulting gel was transferred to a stainless steel reactor lined with polytetrafluoroethylene and statically crystallized at 160 °C for 4 days. After crystallization, the product was centrifuged, washed with deionized water, dried at 100 °C for 12 h, and then calcined at 600 °C for 6 h to obtain H-type SSZ-13 molecular sieve.

[0062] 1.0 g of the above-mentioned H-type SSZ-13 molecular sieve was mixed with 50 mL of 0.1 mol / L Cu(NO3)2 aqueous solution and subjected to ion exchange at 80°C for 4 h. This process was repeated three times to ensure complete exchange. After washing and drying, the exchanged product was calcined at 550°C for 6 h to obtain the Cu-SSZ-13 catalyst.

[0063] (2) Preparation of modified molecular sieve catalyst CS-K5 Take 8.0 g of a mixed solvent of ethanol and water (volume ratio 19:1) and adjust the pH to 8.5 with ammonia. Add 0.03 g of KH550 and stir to ensure complete hydrolysis. Add 1.0 g of the Cu-SSZ-13 catalyst prepared above and sonicate for 5 min to ensure uniform dispersion. Place the mixture in a 90 °C water bath and stir under closed conditions (300 rpm) for 3 h. Then open the container lid and evaporate to dryness at 80 °C. Add 8.0 g of fresh ethanol / water (19:1) mixed solvent to the dried solid and stir under closed conditions for 1 h to dissolve unreacted KH550. Finally, remove the physically adsorbed coupling agent by centrifugation and repeated washing with ethanol. Dry the resulting solid at 100 °C for 12 h to obtain silanized modified molecular sieve.

[0064] In a three-necked flask containing 15 g DMF, add 2.01 g ODA and stir mechanically until completely dissolved. Add 2.99 g BPDA in three slow batches, maintaining an ODA:BPDA ratio of 1:1.01. Stir until completely dissolved after each addition, with intervals of approximately 30 min. After all additions are complete, continue rapid stirring for 6 h to obtain a pale yellow, viscous 25 wt% PAA solution. Allow to stand for 12 h to remove bubbles before use.

[0065] (3) Preparation of PAA fiber membrane The PAA fiber membrane was placed in a muffle furnace and subjected to step heat treatment in air atmosphere: the temperature was increased to 150 °C at a rate of 2 °C / min and held for 30 min; then increased to 250 °C and held for 30 min; finally, the temperature was increased to 300 °C and held for 2 h. After the process was completed, the membrane was allowed to cool naturally to room temperature to obtain the final polyimide membrane.

[0066] (4) CS-K5 was loaded onto PAA fiber membrane to prepare CS-K5-PAA precursor membrane. Weigh 0.5 g of CS-K5 molecular sieve and disperse it in 1 L of ethanol. Sonicate for 1 h, then mechanically stir for 0.5 h to form a stable suspension. Fix the prepared PAA fiber membrane (13 cm × 22 cm) onto a self-made roller device and vertically immerse it in the suspension. Turn on the cantilever stirrer and stir at 100 rpm at room temperature for 6 h to ensure the molecular sieve is fully loaded onto the fibers. After removing the membrane, wash it with ethanol for 30 min to remove the physically adsorbed molecular sieve from the surface, and dry it at 35 °C for 0.5 h to obtain the CS-K5-PAA precursor membrane.

[0067] (5) Preparation of bifunctional membranes The CS-K5-PAA precursor membrane was placed in a muffle furnace and subjected to step heat treatment in air: the temperature was increased to 150°C at a rate of 2 °C / min and held for 30 min; then increased to 250 °C and held for 30 min; finally, the temperature was increased to 300 °C and held for 2 h. After the process was completed, it was allowed to cool naturally to room temperature to obtain the final polyimide-based catalytic membrane (bifunctional membrane). The actual molecular sieve loading was calculated to be 58 wt%, hence the name 58CS-K5-PI.

[0068] The denitrification performance of the fabricated bifunctional membrane was tested in a fixed-bed reactor. The reaction temperature was 100-300 °C. Catalyst evaluation conditions: 500 ppm NO, 500 ppm NH3, 8 v% O2, N2 as equilibrium gas, GHSV for 60,000 h⁻¹. -1The total gas flow rate was 200 ml / min. During the reaction evaluation, the denitrification rate of 58CS-K5-PI at 225 °C was recorded as 100% using a gas analyzer (Testo®340).

[0069] The filtration efficiency and pressure drop of the dual-function membrane were tested using an LZC-K1 filter media performance tester manufactured by Suzhou Huada Equipment Co., Ltd. The aerosol generator continuously generated approximately 450,000 particles. The specific test method for dust removal performance was in accordance with the "Technical Requirements for Bag Filters" (GB / T 6719-2009). The filtration velocity was 1.0 m / min. The test results were: PM0.3 filtration efficiency of 58CS-K5-PI was 86.7%, and the pressure drop was 436.3 Pa. Comparative Example 1

[0070] 3.13 g of HY molecular sieve (Si / Al=20), 0.195 g of Al(OH)3, and 16.885 g of TMAdaOH aqueous solution (25 wt%) were mixed thoroughly, and 8.170 g of water was evaporated by stirring at 80 °C. The resulting gel was transferred to a stainless steel reactor lined with polytetrafluoroethylene and statically crystallized at 160 °C for 4 days. After crystallization, the product was centrifuged, washed with deionized water, dried at 100 °C for 12 h, and then calcined at 600 °C for 6 h to obtain H-type SSZ-13 molecular sieve.

[0071] 1.0 g of the above-mentioned H-type SSZ-13 molecular sieve was mixed with 50 mL of 0.1 mol / L Cu(NO3)2 aqueous solution, and ion exchange was carried out at 80°C for 4 h. This process was repeated three times to ensure complete exchange. After washing and drying, the exchange product was calcined at 550°C for 6 h to obtain the Cu-SSZ-13 catalyst, named CS.

[0072] The denitrification performance of the Cu-SSZ-13 catalyst was tested in a fixed-bed reactor. The reaction temperature was 100-300 °C. Catalyst evaluation conditions: 500 ppm NO, 500 ppm NH3, 8 v% O2, N2 as equilibrium gas, GHSV for 60,000 h⁻¹. -1 The total gas flow rate was 200 ml / min. During the reaction evaluation, the denitrification rate of the Cu-SSZ-13 catalyst at 225 °C was recorded as 94.8% using a gas analyzer (Testo®340). Comparative Example 2

[0073] 3.13 g of HY molecular sieve (Si / Al=20), 0.195 g of Al(OH)3, and 16.885 g of TMAdaOH aqueous solution (25 wt%) were mixed thoroughly, and 8.170 g of water was evaporated by stirring at 80 °C. The resulting gel was transferred to a stainless steel reactor lined with polytetrafluoroethylene and statically crystallized at 160 °C for 4 days. After crystallization, the product was centrifuged, washed with deionized water, dried at 100 °C for 12 h, and then calcined at 600 °C for 6 h to obtain H-type SSZ-13 molecular sieve.

[0074] 1.0 g of the above-mentioned H-type SSZ-13 molecular sieve was mixed with 50 mL of 0.1 mol / L Cu(NO3)2 aqueous solution and subjected to ion exchange at 80°C for 4 h. This process was repeated three times to ensure complete exchange. After washing and drying, the exchanged product was calcined at 550°C for 6 h to obtain the Cu-SSZ-13 catalyst.

[0075] Take 8.0 g of a mixed solvent of ethanol and water (volume ratio 19:1) and adjust the pH to 8.5 with ammonia. Add 0.01 g of H550 and stir to ensure complete hydrolysis. Add 1.0 g of the Cu-SSZ-13 catalyst prepared above and sonicate for 5 min to ensure uniform dispersion. Place the mixture in a 90 °C water bath and stir under closed conditions (300 rpm) for 3 h. Then open the container lid and evaporate to dryness at 80 °C. Add 8.0 g of fresh ethanol / water (19:1) mixed solvent to the dried solid and stir under closed conditions for 1 h to dissolve unreacted KH550. Finally, remove the physically adsorbed coupling agent by centrifugation and repeated washing with ethanol. Dry the resulting solid at 100 °C for 12 h to obtain the silanized modified CS-K5 catalyst.

[0076] The denitrification performance of the CS-K5 catalyst was tested in a fixed-bed reactor. The reaction temperature was 100-300°C. Catalyst evaluation conditions: 500 ppm NO, 500 ppm NH3, 8 v% O2, N2 as equilibrium gas, GHSV for 60,000 h. -1 The total gas flow rate was 200 ml / min. During the reaction evaluation, the denitrification rate of the CS-K5 catalyst at 225 °C was recorded as 97.5% using a gas analyzer (Testo®340). Comparative Example 3

[0077] In a three-necked flask containing 15 g DMF, add 2.01 g ODA and stir mechanically until completely dissolved. Add 2.99 g BPDA in three slow batches, maintaining an ODA:BPDA ratio of 1:1.01. Stir until completely dissolved after each addition, with intervals of approximately 30 min. After all additions are complete, continue rapid stirring for 6 h to obtain a pale yellow, viscous 25 wt% PAA solution. Allow to stand for 12 h to remove bubbles before use.

[0078] The PAA solution was loaded into a syringe for electrospinning. The main parameters were set as follows: voltage 19.5 kV, feed rate 0.5 mL / h, receiver distance 14 cm, receiver rotation speed 200 r / min, oscillation amplitude 25.5 cm, and oscillation speed 2.4 mm / s. The ambient temperature was controlled at 25±5 °C, and the humidity at 40±5%. Oiled paper was placed over the receiver to collect a uniform PAA fiber membrane.

[0079] The PAA fiber membrane was placed in a muffle furnace and subjected to step heat treatment in air atmosphere: the temperature was increased to 150 °C at a rate of 2 °C / min and held for 30 min; then increased to 250 °C and held for 30 min; finally, the temperature was increased to 300 °C and held for 2 h. After the process was completed, the membrane was allowed to cool naturally to room temperature to obtain the final polyimide (PI) membrane.

[0080] The denitrification performance of the aforementioned polyimide membrane was tested in a fixed-bed reactor. The reaction temperature was 100-300°C. Catalyst evaluation conditions: 500 ppm NO, 500 ppm NH3, 8 v% O2, N2 as equilibrium gas, GHSV for 60,000 h. -1 The total gas flow rate was 200 ml / min. During the reaction evaluation, the denitrification rate of the polyimide membrane at 225 °C was recorded as 9.8% using a gas analyzer (Testo® 340).

[0081] The filtration efficiency and pressure drop of fiber membranes with different particle sizes were tested using an LZC-K1 filter media performance tester manufactured by Suzhou Huada Equipment Co., Ltd. The aerosol generator continuously generated approximately 450,000 particles. The specific test method for dust removal performance was in accordance with the "Technical Requirements for Bag Filters" (GB / T 6719-2009). The filtration velocity was 1.0 m / min. The test results were as follows: the PM0.3 filtration efficiency of the polyimide membrane was 37.2%, and the pressure drop was 33.5 Pa.

[0082] Figure 1SEM images of the samples prepared in Examples 1-4 and Comparative Examples 1-3 are shown. The CS samples showed slight agglomeration, which improved after grafting with a coupling agent. With a fixed spinning solution concentration, the PI fiber size was approximately 535 nm. After molecular sieve loading, the actual fiber loading initially increased and then decreased with increasing zeolite addition. SEM images show that at lower loading levels, insufficient surface coverage led to a reduction in active sites; while excessive loading caused zeolite agglomeration and detachment due to interfacial incompatibility. In contrast, the membrane with the optimal loading exhibited a uniform distribution, without substrate exposure or particle aggregation.

[0083] Figure 2 This graph compares the denitrification performance of samples prepared in Examples 1-4 and Comparative Examples 1-3. The graph represents NO. x Conversion curve, with the horizontal axis representing the reaction temperature (100-300 °C) and the vertical axis representing NO. x Conversion rate (%). The results showed that the CS-K5 sample, after grafting with the coupling agent, performed better than the CS sample, while the PI fiber showed almost no denitrification performance. After loading the fiber membrane, the denitrification performance showed a significant positive correlation with the increase of molecular sieve loading. For the sample with a loading of 48 wt%, NO at 200 °C was [missing value]. x The conversion rate was 68.4%; with the loading increased to 54 wt%, the conversion rate increased to 75.1%; and with a loading of 61 wt%, the conversion rate reached 80.9%. After exceeding the fiber's carrying capacity, the molecular sieve loading decreased, and the corresponding denitrification performance also declined. The core reason for this trend is that the CS-K5 molecular sieve is the active core of the NH3-SCR reaction. The higher the loading, the more abundant the number of Cu active sites distributed on the surface of the 25PI fiber carrier, thus enhancing the denitrification performance. Furthermore, the denitrification activity of all loading samples first increased and then stabilized with increasing temperature (becoming relatively stable after 250 °C), and showed good activity in the low-temperature range of 200-250 °C. This proves that the 25PI carrier has no negative impact on the dispersibility of the molecular sieve, and that a gradient improvement in denitrification performance can be achieved simply by adjusting the loading, providing direct data support for the optimal loading for high denitrification and low energy consumption.

[0084] Figure 3 This is a comparison chart of the filtration performance of samples prepared in Examples 1-4 and Comparative Examples 1-3. It compares the filtration performance of pure PI units with catalytic membranes of different molecular sieve loadings. The data shows that filtration performance increases with increasing molecular sieve loading. The sample with a loading of 61 wt% (i.e., 61CS-K5-PI) has the highest filtration efficiency (99.99%) and a pressure drop of 620 Pa, meeting industrial-grade pressure drop and emission requirements.

[0085] Figure 4The results show the stability test of the sample prepared in Example 1. Figure (a) is the monitoring curve after continuous operation at 225 °C for 250 h. The results show that the catalyst loading rate decreased from 60.65 wt% to 60.28 wt% within 250 h, with a loss of only 0.37%, showing no significant decrease. Combined with the monitoring data from the quartz crystal microbalance (QCM) (Figure b), the frequency did not fluctuate significantly after ethanol washing, proving that the CS-K5 and PI fiber are irreversibly covalently bonded, with no risk of catalyst detachment, thus verifying the long-term operational stability of the bifunctional membrane.

[0086] Figure 5 This image shows SEM images of the sample prepared in Example 1 before and after cleaning. The image before cleaning shows that the fiber surface is uniformly covered with CS-K5 particles, with a small amount of intercepted PM particles attached. The image after cleaning (ethanol cleaning) shows that the PM particles are completely removed, while the CS-K5 particles remain tightly attached to the fiber surface without significant detachment or aggregation, and the fiber network structure remains intact. This image verifies the structural stability of the sample after cleaning from a microscopic morphology perspective, providing structural basis for subsequent cycle performance testing.

[0087] Figure 6 The figure shows the water resistance test results for the samples prepared in Example 1 and Comparative Example 1. The figure also shows the NO content in the reaction system containing 10 vol% H2O. x The conversion rate varies with time (0-40 h) at a test temperature of 225 °C. Results show that the conversion rate of the 61CS-K5-PI sample remained stable at 98-100%, with fluctuations of <2%; the conversion rate of the CS sample decreased to 90% after H2O was introduced due to its superhydrophilic properties. This figure demonstrates that the weakly hydrophobic surface of 61CS-K5-PI effectively inhibits water vapor adsorption, exhibits excellent water resistance, and is suitable for high-humidity industrial flue gas environments.

[0088] Figure 7 The figure shows the sulfur resistance test results of the sample prepared in Example 1. The figure also shows the NO content in the reaction system containing 200 ppm SO2. x The conversion rate versus time (0-20 h) curves were obtained at a test temperature of 225 °C. The results show that even after introducing SO2, the denitrification performance remained above 80%. This figure demonstrates that the CS-K5 molecular sieve in the 61CS-K5-PI sample has a relatively weak adsorption capacity for SO2, exhibits good resistance to sulfur poisoning and regeneration capabilities, and is suitable for sulfur-containing industrial flue gas conditions.

Claims

1. A method for preparing a bifunctional membrane for NH3-SCR and particulate matter filtration, characterized in that, Includes the following steps: (1) The surface of Cu-SSZ-13 molecular sieve catalyst and silane coupling agent were modified in an ethanol-water mixed solution to obtain modified molecular sieve catalyst CS-K5. (2) Prepare a PAA solution as a spinning solution, and spin the PAA solution into a PAA fiber membrane by electrospinning; (3) The modified molecular sieve catalyst CS-K5 is loaded onto the PAA fiber membrane to obtain the CS-K5-PAA precursor membrane; (4) The CS-K5-PAA precursor membrane was subjected to step heating heat treatment to obtain a bifunctional membrane of polyimide-supported Cu-SSZ-13.

2. The method for preparing a bifunctional membrane for NH3-SCR and particulate matter filtration according to claim 1, characterized in that, The preparation method of Cu-SSZ-13 molecular sieve catalyst in step (1) is as follows: H-type FAU molecular sieve, Al(OH)3 and TMAdaOH are used as raw materials. A synthetic gel is prepared by molar ratio of SiO2:0.05 Al2O3:5 H2O:0.4 TMAdaOH. The gel is hydrothermally crystallized at 155-165 °C for 90-100 h. After washing, drying and calcination, H-SSZ-13 is obtained. H-SSZ-13 is added to Cu(NO3)2 solution for ion exchange and calcination to obtain Cu-SSZ-13 molecular sieve catalyst.

3. A method for preparing a bifunctional membrane for NH3-SCR and particulate matter filtration according to claim 1, characterized in that, The surface modification method described in step (1) is as follows: the pH of an ethanol-water mixed solution with a volume ratio of 18-20:1 is adjusted to 8-9, 1-5 wt% of silane coupling agent KH550 and 10 wt% of Cu-SSZ-13 molecular sieve catalyst are added, ultrasonic treatment is performed for 5-10 min, and the reaction is stirred at 60-90 °C for 2.8-3.2 h. The liquid is completely evaporated, then washed and dried to obtain the modified molecular sieve catalyst CS-K5.

4. A method for preparing a bifunctional membrane for NH3-SCR and particulate matter filtration according to claim 1, characterized in that, The PAA solution described in step (2) is prepared by using ODA and BPDA as monomers, with a monomer addition molar ratio of n(ODA):n(BPDA)=1:1.01, and polymerizing in DMF solvent for 5.5-6.5 h to obtain a 20-30 wt% PAA solution.

5. A method for preparing a bifunctional membrane for NH3-SCR and particulate matter filtration according to claim 1, characterized in that, The electrospinning parameters mentioned in step (2) include: voltage 19-20 kV, receiver rotation speed 180-220 r / min, feed speed 0.45-0.55 mL / h, needle tip to receiver distance 13-15 cm, oscillation amplitude 25-26 cm, oscillation speed 2.3-2.5 mm / s, temperature 25±5 °C, and humidity 40±5%.

6. A method for preparing a bifunctional membrane for NH3-SCR and particulate matter filtration according to claim 1, characterized in that, Step (3) is as follows: The modified molecular sieve catalyst CS-K5 is dispersed in ethanol, sonicated for 0.8-1.2 h, and stirred for 0.4-0.6 h to obtain a suspension with a CS-K5 content of 52-73 wt%. Then, the PAA fiber membrane is immersed in the suspension and stirred for 5.5-6.5 h to load the modified molecular sieve catalyst CS-K5 onto the PAA fiber membrane. Finally, it is washed and dried to obtain the CS-K5-PAA precursor membrane.

7. A method for preparing a bifunctional membrane for NH3-SCR and particulate matter filtration according to claim 1, characterized in that, The heat treatment described in step (4) is as follows: heat to 140-160 °C at a rate of 1.8-2.2 °C / min and hold for 25-35 min; continue to heat to 240-260 °C and hold for 25-35 min; then heat to 290-310 °C and hold for 1.8-2.2 h, and cool naturally to room temperature.

8. A method for preparing a bifunctional membrane for NH3-SCR and particulate matter filtration according to claim 1, characterized in that, The loading of the modified molecular sieve catalyst CS-K5 in the obtained bifunctional membrane was 48-61 wt.

9. The bifunctional membrane obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the bifunctional membrane obtained by the preparation method according to any one of claims 1 to 8 in NH3-SCR and particulate matter filtration.

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