A method for preparing CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst

Abstract

The application relates to a preparation method of a CuO-CeO2 / ZSM-5 (MW) automobile exhaust catalyst, and relates to a preparation method of a molecular sieve catalyst. The application aims at solving the technical problems of high cost, poor low-temperature performance and easy sintering at high temperature of the existing automobile exhaust purification catalyst. The method comprises the following steps: placing ZSM-5 molecular sieve into a NaOH solution to obtain a mixed solution; microwave treating the mixed solution in a corrosion-resistant and microwave radiation-resistant container, then ion exchanging the mixed solution with an ammonium chloride solution, and then roasting to obtain ZSM-5 (MW); immersing the microwave modified ZSM-5 (MW) molecular sieve into a copper-cerium mixed salt solution, and then roasting to obtain the CuO-CeO2 / ZSM-5 (MW) automobile exhaust catalyst. The catalyst can reach the light-off temperature at 120 DEG C, and the conversion rates of CO and NO double pollutants can be kept at 90% to 100% in a wide temperature range of 165 DEG C to 500 DEG C, and the catalyst can be used in the field of automobile exhaust treatment.

Description

Technical Field

[0001] This invention relates to a method for preparing molecular sieve catalysts. Background Technology

[0002] Motor vehicle exhaust is one of the main sources of air pollutants, with major pollutants including carbon monoxide (CO) and nitrogen oxides (NOx). x Pollutants such as hydrocarbons (HC) pose significant threats to human health and the environment. Mobile source exhaust gas removal often employs three-way catalysts, with catalyst coatings including γ-Al₂O₃, rare earth-transition metal composite oxides, and core active components such as Pt, Rh, and Pd, all precious metals. While these catalysts can achieve synergistic conversion of multiple pollutants under specific conditions, their core active components are expensive. Furthermore, three-way catalysts perform poorly under low-temperature conditions (such as engine cold starts and low-temperature industrial exhaust emissions), failing to effectively treat pollutants in low-temperature exhaust gases. Additionally, these three-way catalysts are prone to sintering at high temperatures, resulting in poor durability. Summary of the Invention

[0003] This invention aims to address the technical problems of existing automotive exhaust purification catalysts, such as high cost, poor low-temperature performance, and easy sintering at high temperatures, by providing a method for preparing CuO-CeO2 / ZSM-5(MW) automotive exhaust catalyst. The CuO-CeO2 / ZSM-5(MW) automotive exhaust catalyst prepared by this invention through microwave alkali treatment has the characteristics of wide temperature range, high activity, and high stability.

[0004] The preparation method of the CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst of the present invention is carried out according to the following steps:

[0005] 1. Add ZSM-5 molecular sieve to a corrosion-resistant and microwave-resistant container, then add NaOH solution with a concentration of 0.2-0.5 mol / L, stir and mix evenly, then transfer the container to a microwave oven with a power of 800-900 W for 5-10 s, then centrifuge and wash until neutral, transfer the solid to an oven to dry, and obtain alkali-treated ZSM-5 molecular sieve;

[0006] 2. Add the alkali-treated ZSM-5 molecular sieve to an ammonium chloride solution with a concentration of 1~1.5 mol / L, and maintain the temperature at 80~90℃ for 2~4 h for ion exchange; then centrifuge to separate the solid and wash it twice with deionized water; repeat the ion exchange and washing operation 2~3 times, and then transfer the solid to an oven to dry to obtain ammonium-treated ZSM-5 molecular sieve.

[0007] 3. The ammonium-treated ZSM-5 molecular sieve is placed in a muffle furnace and heated to 500℃~550℃ for 4~6 h for calcination to obtain ZSM-5 (MW); In this ZSM-5 (MW) molecular sieve, MW is an abbreviation for Microwave, which refers to the ZSM-5 molecular sieve modified by microwave-assisted heat treatment.

[0008] IV. Cu(NO3)2 . 3H2O and Ce(NO3)3 . 6H2O was dissolved in water to obtain a salt solution. The salt solution was added dropwise to ZSM-5(MW) in small amounts multiple times using a pipette. After each addition, the mixture was stirred thoroughly before the next addition was made. After all the additions were completed, the impregnated molecular sieve was obtained. The molar ratio of Cu:(Cu+Ce) in the salt solution was controlled at 10%~20%, and the mass percentage content of CuO-CeO2 in the support ZSM-5(MW) was controlled at 10%~25%.

[0009] 5. After the impregnated molecular sieve is dried in an oven, it is placed in a muffle furnace and heated to 350-450 ℃ and kept for 2-5 h for calcination to obtain CuO-CeO2 / ZSM-5(MW) automotive exhaust catalyst.

[0010] Furthermore, the mass ratio of the ZSM-5 molecular sieve mentioned in step one to the volume ratio of the NaOH solution with a concentration of 0.2 to 0.5 mol / L is 1 g : (25 to 42) mL.

[0011] Furthermore, the drying described in step one is performed at a temperature of 60–100 °C for 6–12 h.

[0012] Furthermore, in step two, the ratio of the mass of the alkali-treated ZSM-5 molecular sieve to the volume of the ammonium chloride solution with a concentration of 1~1.5mol / L is 1g:(25~40)mL.

[0013] Furthermore, the drying process described in step two involves drying at a temperature of 60–100 °C for 6–12 hours.

[0014] Furthermore, in step four, the salt solution contains 6.53–34.6 mg of Cu(NO3)2. . 3H2O and 99.5–263.8 mg Ce(NO3)3 . It is obtained by dissolving 6H2O in 300-350 μl of water; then the salt solution is added dropwise and impregnated onto 440 mg ZSM-5 (MW).

[0015] Furthermore, the drying described in step five is performed at a temperature of 60–100°C for 6–12 hours.

[0016] Furthermore, the preparation method of ZSM-5 molecular sieve described in step one is carried out according to the following steps:

[0017] (1) Mix silicon source, aluminum source and water in a molar ratio of 1:0.005:(5~35) to obtain a mixed solution;

[0018] (2) Under stirring conditions, the template agent is added dropwise to the mixture. After the addition is completed, stirring is continued for 6 to 6.5 h to obtain the mixed mother liquor;

[0019] (3) The mixed mother liquor is transferred to a reactor lined with polytetrafluoroethylene and crystallized at a temperature of 150-200 °C for 72-80 h. After crystallization, it is cooled to room temperature, centrifuged and washed, and then dried to obtain the precursor.

[0020] (4) Place the precursor in a muffle furnace and heat it to 500-600 ℃ for 5-10 h to obtain ZSM-5 molecular sieve.

[0021] Furthermore, the template agent mentioned in step one (2) is tetrapropylammonium hydroxide, tetrapropylammonium bromide, ethylenediamine or n-butylammonium.

[0022] Furthermore, the molar ratio of the template agent described in step one (2) to the silicon source described in step one (1) is 1:(0.34~0.42).

[0023] Furthermore, the drying described in step one (3) is carried out at a temperature of 60 to 100 °C for 6 to 12 hours.

[0024] This invention modifies the ZSM-5 support through short-time microwave alkaline treatment. While preserving the molecular sieve (MFI) topological framework and maintaining high crystallinity, it controls the pore structure of the support, increasing the specific surface area and pore volume to confine the CuO-CeO2 active component, thereby preventing particle migration, aggregation, and sintering. Simultaneously, because the CuO-CeO2 active component is confined within the pores, the contact efficiency between locally enriched CO and NO reactants and the active sites is improved, enhancing the reaction activity. The modified support also regulates the crystal structure and increases the number of surface defect sites, significantly improving CO-SCR. The CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst of this invention exhibits excellent low-temperature catalytic activity, reaching the ignition temperature (T0) at 120°C. 50Furthermore, the conversion rates of both CO and NO pollutants remain at 90-100% within a wide temperature range of 165 to 500°C, which improves the catalyst's poor performance under low-temperature conditions (such as engine cold starts and low-temperature emissions from industrial exhaust). In addition, the preparation method of this invention is mild and controllable, easily scalable, and uses only inexpensive and abundant transition metals (Cu, Ce), eliminating dependence on precious metals. It can be used in the field of air pollutant control. Attached Figure Description

[0025] Figure 1 These are scanning electron microscope (SEM) images of the CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalysts prepared in Examples 1 and 2, and the CuO-CeO2 / ZSM-5 catalyst prepared in Comparative Example 1.

[0026] Figure 2 The images show the XRD patterns of the CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalysts prepared in Examples 1 and 2, and the CuO-CeO2 / ZSM-5 catalyst prepared in Comparative Example 1.

[0027] Figure 3 The N2 adsorption-desorption isotherms and full pore size distribution diagrams of ZSM-5 (MW) prepared in step three of Examples 1 and 2 and ZSM-5 of Comparative Example 1 are shown.

[0028] Figure 4 The N2 adsorption-desorption isotherms and full pore size distribution diagrams of CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalysts prepared in Examples 1 and 2 and the catalyst CuO-CeO2 / ZSM-5 of Comparative Example 1 are shown.

[0029] Figure 5 The graphs show the relationship between the CO conversion rate and temperature of the molecular sieve catalysts prepared in Examples 1, 2, 3 and Comparative Example 1.

[0030] Figure 6 The graphs show the relationship between the conversion rate of NO to the molecular sieve catalysts prepared in Examples 1, 2, 3 and Comparative Example 1 and temperature.

[0031] Figure 7 This is a stability performance diagram of the CuO-CeO2 / ZSM-5(MW) automotive exhaust catalyst prepared in Example 1. Detailed Implementation

[0032] The beneficial effects of the present invention are verified using the following examples:

[0033] Example 1: The preparation method of the CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst in this example is carried out according to the following steps:

[0034] 1. Add 600 mg of ZSM-5 molecular sieve to a polytetrafluoroethylene beaker, then add 15 ml of 0.5 mol / L NaOH solution, stir and mix for 15 min to make it uniform, then put the polytetrafluoroethylene beaker into a household microwave oven with a power of 900W for 5 s, then centrifuge and wash until neutral, transfer the solid to an oven and dry it at a temperature of 60 ℃ for 10 h to obtain alkali-treated ZSM-5 molecular sieve;

[0035] The preparation method of ZSM-5 molecular sieve is as follows:

[0036] (1) Add 8.32 g of tetraethyl orthosilicate (TEOS) and 0.041 g of aluminum isopropoxide to 15 mL of deionized water and stir until the mixture is homogeneous to obtain a mixture;

[0037] (2) Under stirring conditions, 13 g of tetrapropylammonium hydroxide (TPAOH) solution with a mass percentage concentration of 25% was added dropwise to the mixture. After the addition was completed, stirring was continued for 6 h to obtain the mixed mother liquor.

[0038] (3) Transfer the mixed mother liquor to a 100 mL polytetrafluoroethylene-lined reactor and crystallize it at 170 °C for 3 days. After crystallization, cool it to room temperature, centrifuge and wash it, and then dry it at 60 °C for 10 h to obtain the precursor.

[0039] (4) The precursor was placed in a muffle furnace and heated to 550 °C for 6 h to obtain ZSM-5 molecular sieve.

[0040] 2. Add the alkali-treated ZSM-5 molecular sieve to a round-bottom flask, then add 20 ml of 1 mol / L ammonium chloride solution to the round-bottom flask, and perform ion exchange at 80℃ for 2 h; then centrifuge to separate the solid and wash it twice with deionized water; repeat the ion exchange and washing operation 3 times, then transfer the solid to an oven and dry it at 60℃ for 10 h to obtain ammonium-treated ZSM-5 molecular sieve;

[0041] 3. The ammonium-treated ZSM-5 molecular sieve was placed in a muffle furnace and heated to 550℃ for 6 hours to obtain ZSM-5 (MW);

[0042] IV. 20.2 mg of Cu(NO3)2 . 3H2O and 205.4 mg Ce(NO3)3 .6H₂O was dissolved in 320 μl of water to obtain a salt solution. This salt solution was then added dropwise (3 μl each time) to 440 mg ZSM-5(MW) using a pipette. After each addition, the solution was stirred with a glass rod until completely and uniformly dispersed before the next addition. After the addition was complete, the impregnated molecular sieve was obtained. The mass percentage content of CuO-CeO₂ in the ZSM-5(MW) support was 20 wt%.

[0043] 5. The impregnated molecular sieve was placed in an oven and dried at 60°C for 10 h. Then it was placed in a muffle furnace, heated to 400°C and kept at 4 h for calcination to obtain CuO-CeO2 / ZSM-5(MW) automotive exhaust catalyst.

[0044] Example 2: The difference between this example and Example 1 is that the microwave processing time in step one is 7 seconds; the other steps and parameters are the same as in Example 1.

[0045] Example 3: The difference between this example and Example 1 is that the microwave processing time in step one is 10 s; the other steps and parameters are the same as in Example 1.

[0046] Comparative Example 1: This comparison involves the preparation of catalysts without microwave alkali treatment. The specific steps are as follows:

[0047] I. Preparation of ZSM-5 molecular sieve, the specific steps are as follows:

[0048] (1) Add 8.32 g of tetraethyl orthosilicate (TEOS) and 0.041 g of aluminum isopropoxide to 15 mL of deionized water and stir until the mixture is homogeneous to obtain a mixture;

[0049] (2) Under stirring conditions, 13 g of tetrapropylammonium hydroxide (TPAOH) solution with a mass percentage concentration of 25% was added dropwise to the mixture. After the addition was completed, stirring was continued for 6 h to obtain the mixed mother liquor.

[0050] (3) Transfer the mixed mother liquor to a 100 mL polytetrafluoroethylene-lined reactor and crystallize it at 170 °C for 3 days. After crystallization, cool it to room temperature, centrifuge and wash it, and then dry it at 60 °C for 10 h to obtain the precursor.

[0051] (4) The precursor was placed in a muffle furnace and heated to 550 °C for 6 h to obtain ZSM-5 molecular sieve.

[0052] II. 20.2 mg of Cu(NO3)2 . 3H2O and 205.4 mg Ce(NO3)3. 6H₂O was dissolved in 320 μl of water to obtain a salt solution. This salt solution was then added dropwise (3 μl each time) to 440 mg of ZSM-5 using a pipette. After each addition, the solution was stirred with a glass rod until completely and evenly dispersed before the next addition. After the addition was complete, the impregnated molecular sieve was obtained. The mass percentage of CuO-CeO₂ in the ZSM-5 support was controlled at 20 wt%.

[0053] 3. The impregnated molecular sieve was placed in an oven and dried at 60 °C for 10 h. Then it was placed in a muffle furnace, heated to 400 °C and kept at 4 h for calcination to obtain a comparative catalyst, denoted as CuO-CeO2 / ZSM-5.

[0054] Figure 1 These are scanning electron microscope (SEM) images of the CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalysts prepared in Examples 1 and 2, and the CuO-CeO2 / ZSM-5 catalyst prepared in Comparative Example 1; where a is the CuO-CeO2 / ZSM-5 catalyst prepared in Comparative Example 1, b is the CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst prepared in Example 1, and c is the CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst prepared in Example 2. Figure 1 As can be seen from a, the catalyst support is a ZSM-5 molecular sieve with a hexagonal prism morphology of MFI topology. The ZSM-5 molecular sieve has a size of about 200 nm, with regular grain outlines and clear edges. Most of the CuO-CeO2 active components are uniformly distributed on the surface of the molecular sieve support in the form of fine particles, while a few active components are aggregated together and cover the surface of the molecular sieve support. Figure 1 As can be seen from b, the molecular sieve support of the CuO-CeO2 / ZSM-5(MW) automotive exhaust catalyst prepared in Example 1 still maintains a complete hexagonal prism morphology, and the grain morphology is not significantly different from that of the original support; the dispersion of CuO-CeO2 active components on the support surface is further optimized, the particle size of active particles is more uniform, and no large particle agglomerates appear, indicating that the short-time modified support with microwave treatment for 5s can achieve efficient and uniform loading of active components. Figure 1 As can be seen from c, the molecular sieve ZSM-5 support crystal of CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst prepared in Example 2 has significantly blunted edges and corners, and the crystal morphology tends to be rounded short columnar. The surface roughness of the support is significantly improved, providing more attachment sites for the active components. The CuO-CeO2 active components are highly uniformly loaded and anchored on the support surface, with no obvious agglomeration.

[0055] Figure 2These are the XRD spectra of the CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalysts prepared in Examples 1 and 2, and the CuO-CeO2 / ZSM-5 catalyst prepared in Comparative Example 1; from Figure 2 It can be seen that the diffraction peak positions of ZSM-5 after microwave alkaline treatment did not shift compared to untreated ZSM-5, and no impurity peaks appeared. This indicates that short-term microwave alkaline treatment did not destroy the molecular sieve framework topology of ZSM-5, achieving the purpose of etching and controlling the surface and pores of the support. After impregnation with the active component, characteristic diffraction peaks of CeO2 were found in all supported samples, but sharp characteristic diffraction peaks of CuO were not detected. This may be because the CuO content was too low, below the detection limit, and was in a highly dispersed state.

[0056] Figure 3 These are the N2 adsorption-desorption isotherm curves and full pore size distribution diagrams of ZSM-5 (MW) prepared in step three of Examples 1 and 2, and ZSM-5 of Comparative Example 1; where a is the N2 adsorption-desorption isotherm curve and b is the pore size distribution diagram. Figure 3 As can be seen from a, both the untreated ZSM-5 and the ZSM-5 (MW) modified in step three of Example 1 exhibit Type I isothermal adsorption curves. In the low-pressure range (P / P0 < 0.1), the nitrogen adsorption capacity increases rapidly, characteristic of ZSM-5 microporous monolayer adsorption. In the medium- and high-pressure range, the adsorption capacity increases gradually, with a sharp increase in adsorption capacity when P / P0 approaches 1, originating from multilayer adsorption between particles. The ZSM-5 (MW) sample modified in step three of Example 2 exhibits a Type IV isothermal adsorption curve with a weak, narrow-range hysteresis loop. From... Figure 3 As shown in the pore size distribution diagram (b), short-time microwave treatment broadened the inherent micropore size of ZSM-5 and created additional micropores in the 12-20 Å range. The modified ZSM-5 exhibited a low-intensity signal in the 20-40 Å mesoporous region, indicating that the modification could achieve controllable etching. A multi-level microporous-mesoporous structure was constructed while retaining the original microporous framework. This modification can unblock pore channels, ensuring that active components can enter the pores and achieve the pore confinement effect of molecular sieves. Specific data are shown in Table 1.

[0057] Table 1. Specific surface area and pore volume of molecular sieve ZSM-5 and modified ZSM-5 (MW).

[0058] project ZSM-5 (Comparative Example 1) ZSM-5 (MW) of Example 1 ZSM-5 (MW) of Example 2 BET surface area (m² / g) 370.7710 444.93 455.66 Pore ​​volume (cm³ / g) 0.272433 0.351594 0.419254

[0059] from Figure 3 As shown in Table 1, short-time microwave treatment increases the specific surface area and pore volume of ZSM-5, which can further improve the dispersion of active components and avoid large particle agglomeration. At the same time, the larger pore volume has a certain carbon-holding space, which can delay pore blockage and maintain the long-term activity of the catalytic system.

[0060] Figure 4 These are N2 adsorption-desorption isotherms and full pore size distribution diagrams of the CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalysts prepared in Examples 1 and 2, and the CuO-CeO2 / ZSM-5 catalyst of Comparative Example 1; where a is the N2 adsorption-desorption isotherm and b is the pore size distribution diagram. Figure 4 As can be seen from a, all the CuO-CeO2 / ZSM-5 (MW) catalyst samples prepared in Examples 1 and 2 exhibit typical Type IV isotherms and hysteresis loops. From Figure 4 As can be seen from the full pore size distribution curves of b, all samples retained the microporous characteristic peaks of ZSM-5. Meanwhile, the microwave-modified catalyst still exhibits a significant mesoporous distribution in the 20–40 Å range. This well-developed pore structure provides more dispersion sites for the CuO-CeO2 active components, which is beneficial for the uniform distribution of the active components. Simultaneously, the mesoporous channels can significantly improve the mass transfer efficiency between reactants and products, providing a good structural basis for the excellent activity and stability of the catalyst in the CO-SCR reaction. Specific data are shown in Table 2.

[0061] Table 2. Specific surface area and pore volume of the catalyst.

[0062] project <![CDATA[CuO-CeO2 / ZSM-5 of Comparative Example 1]]> <![CDATA[CuO-CeO2 / ZSM-5 (MW) of Example 1]]> <![CDATA[CuO-CeO2 / ZSM-5 (MW) of Example 2]]> BET surface area (m² / g) 303.0892 386.09 360.24 Pore ​​volume (cm³ / g) 0.239203 0.294582 0.353725

[0063] Comparing the data in Tables 1 and 2, after loading the active component, the specific surface area and total pore volume of all samples decreased to varying degrees. The reduction in pore volume of the microwave-modified CuO-CeO2 / ZSM-5 (MW) catalyst was significantly greater than that of the conventionally prepared CuO-CeO2 / ZSM-5; further combined with Figure 1 SEM results showed that the catalyst prepared by conventional ZSM-5 exhibited agglomeration of active components on its surface, while the microwave-modified ZSM-5 (MW)-based catalyst had intact crystal morphology, uniform active particle size, and no obvious agglomeration. This indicates that the CuO-CeO2 active species successfully entered the porous system of the microwave-modified ZSM-5. Therefore, the pore space of the microwave-modified molecular sieve exerts a unique spatial confinement effect on the CuO-CeO2 particles, and this unique confinement effect can significantly optimize the overall reaction performance of the catalyst.

[0064] ZSM-5 itself possesses regular micropores of approximately 0.52 nm, exhibiting a fixed spatial scale, equivalent to a microscopic "nanoreactor." However, the original ZSM-5 pores are slightly smaller and consist of only a single micropore, resulting in a limited amount of CuO-CeO2 active component entering the pores; most of it is only loaded onto the outer surface of ZSM-5. This leaves CuO-CeO2 in a completely free and unconstrained growth state. Under high-temperature calcination of the catalyst and high-temperature reaction conditions of automotive exhaust, the metal oxide particles have high surface energy, making them highly susceptible to the Oswald ripening effect. This leads to the dissolution of small particles, coarsening of large particles, and extensive aggregation, coverage, and inactivation of active sites, ultimately resulting in a significant decline in the catalyst's high-temperature performance. In contrast, microwave-modified ZSM-5 exhibits multi-level micropores and mesopores, allowing more active components to enter the pores and forming a confined environment—a key factor in achieving high-temperature deactivation resistance. This involves precisely confining CuO-CeO2 grains within the pore cavities, utilizing the geometric barriers of the nanopores to physically block the migration, fusion, and growth of active particles at high temperatures. Even under high-temperature thermal conditions, the confined active grains cannot undergo large-scale slippage or aggregation, maintaining a fine and uniform nanocrystalline state, ensuring that active sites are not lost, stacked, or passivated. Therefore, this unique confinement protection mechanism enables the CuO-CeO2 / ZSM-5 (MW) catalyst to withstand continuous high-temperature thermal shock from automotive exhaust gases, maintaining a complete active morphology, sufficient active sites, and excellent catalytic activity, significantly improving the catalyst's high-temperature performance and service life.

[0065] The conversion rates of CO and NO were investigated using the molecular sieve catalysts prepared in Examples 1, 2, and 3, as well as Comparative Example 1. The tests were conducted in a fixed-bed reactor. The molecular sieve catalysts were added to the fixed-bed reactor, and CO and NO were introduced into the reactor using N2 as a carrier gas. The fixed bed was heated at a rate of 5 °C / min, eventually reaching 500 °C. The conversion rates of CO and NO were tested, and the curves showing the relationship between the conversion rates of CO and NO and temperature are as follows: Figure 5 , 6 As shown, from Figure 5 , 6 It can be seen that when pure CuO-CeO2 is used as a catalyst, the ignition temperature is relatively high, and the activity curve in the mid-to-high temperature range shows a significant decline and fluctuation. This may be due to the poor dispersion of the active component. After loading CuO-CeO2 onto the unmodified ZSM-5 support, the low-temperature activity of the catalyst is significantly improved, but the activity decay phenomenon in the high-temperature range is still obvious. This is because the ZSM-5 support plays a role in dispersing the active component, but does not show a significant confinement effect. The reason is that the pores are too small, and the amount of active component entering the pores is limited, resulting in a bottleneck in high-temperature performance. The catalysts prepared in Examples 1-3 after short-time microwave treatment have low-temperature catalytic activity and can all reach the ignition temperature (Tignition temperature) at 120°C.50 The catalysts prepared in Examples 1-3 maintained a CO and NO dual-pollutant conversion rate of 90%-100% across a wide temperature range of 165-500℃, demonstrating improved performance across the entire temperature spectrum. This is because microwave treatment etched the support surface, cleared the pores, and increased the pore size, pore volume, and surface area, allowing the active components to be uniformly distributed within the pores. Furthermore, these pores confine the active components, reducing their aggregation at high temperatures and thus maintaining their activity.

[0066] The catalyst prepared in Example 1 was subjected to a stability test at 400 °C for 8000 min. Figure 7 As shown, from Figure 7 It can be seen that the CO conversion rate remains above 85%.

Claims

1. A method for preparing a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst, characterized in that, This method is performed in the following steps:

1. Add ZSM-5 molecular sieve to a corrosion-resistant and microwave-resistant container, then add a NaOH solution with a concentration of 0.2-0.5 mol / L, stir and mix evenly, then transfer the container to a microwave oven with a power of 800-900 W for 5-10 s, then centrifuge and wash until neutral, transfer the solid to an oven to dry, and obtain alkali-treated ZSM-5 molecular sieve; 2. Add the alkali-treated ZSM-5 molecular sieve to an ammonium chloride solution with a concentration of 1~1.5 mol / L, and maintain the solution at a temperature of 80~90℃ for 2~4 h to carry out ion exchange. The solid was then separated by centrifugation and washed twice with deionized water; the ion exchange and washing process was repeated 2-3 times, and the solid was then transferred to an oven to dry, yielding ammonium-treated ZSM-5 molecular sieve.

3. The ammonium-treated ZSM-5 molecular sieve was placed in a muffle furnace and heated to 500℃~550℃ for 4~6 h for calcination to obtain ZSM-5 (MW); IV. Cu(NO3)2 . 3H2O and Ce(NO3)3 . 6H2O was dissolved in water to obtain a salt solution. The salt solution was added dropwise to ZSM-5(MW) in small amounts multiple times using a pipette. After each addition, the mixture was stirred thoroughly before the next addition was made. After all the additions were completed, the impregnated molecular sieve was obtained. The molar ratio of Cu:(Cu+Ce) in the salt solution was controlled at 10%~20%, and the mass percentage content of CuO-CeO2 in the support ZSM-5(MW) was controlled at 10%~25%.

5. After the impregnated molecular sieve is dried in an oven, it is placed in a muffle furnace and heated to 350-450 ℃ and kept for 2-5 h for calcination to obtain CuO-CeO2 / ZSM-5(MW) automotive exhaust catalyst.

2. The preparation method of a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst according to claim 1, characterized in that, The mass ratio of the ZSM-5 molecular sieve mentioned in step one to the volume ratio of the NaOH solution with a concentration of 0.2 to 0.5 mol / L is 1 g : (25 to 42) mL.

3. The preparation method of a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst according to claim 1 or 2, characterized in that, The drying process described in step one involves maintaining the temperature at 60–100 °C for 6–12 hours.

4. The preparation method of a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst according to claim 1 or 2, characterized in that, In step two, the ratio of the mass of the alkali-treated ZSM-5 molecular sieve to the volume of the ammonium chloride solution with a concentration of 1~1.5 mol / L is 1g:(25~40)mL.

5. A method for preparing a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst according to claim 1 or 2, characterized in that, The drying process described in step two involves maintaining the temperature at 60–100 °C for 6–12 hours.

6. A method for preparing a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst according to claim 1 or 2, characterized in that, In step four, the salt solution contains 6.53–34.6 mg of Cu(NO3)2. . 3H2O and 99.5–263.8 mg Ce(NO3)3 . It is obtained by dissolving 6H2O in 300-350 μl of water; then the salt solution is added dropwise and impregnated onto 440 mg ZSM-5 (MW).

7. A method for preparing a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst according to claim 1 or 2, characterized in that, The preparation method of ZSM-5 molecular sieve described in step one is carried out according to the following steps: (1) Mix silicon source, aluminum source and water in a molar ratio of 1:0.005:(5~35) to obtain a mixed solution; (2) Under stirring conditions, the template agent is added dropwise to the mixture. After the addition is completed, stirring is continued for 6 to 6.5 h to obtain the mixed mother liquor; (3) The mixed mother liquor is transferred to a reactor lined with polytetrafluoroethylene and crystallized at a temperature of 150-200 °C for 72-80 h. After crystallization, it is cooled to room temperature, centrifuged and washed, and then dried to obtain the precursor. (4) Place the precursor in a muffle furnace and heat it to 500-600 ℃ for 5-10 h to obtain ZSM-5 molecular sieve.

8. The method for preparing a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst according to claim 7, characterized in that, The template agent mentioned in step one (2) is tetrapropylammonium hydroxide, tetrapropylammonium bromide, ethylenediamine or n-butylammonium.

9. The method for preparing a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst according to claim 7, characterized in that, The molar ratio of the template agent mentioned in step one (2) to the silicon source mentioned in step one (1) is 1: (0.34~0.42).

10. The method for preparing a CuO-CeO2 / ZSM-5 (MW) automotive exhaust catalyst according to claim 7, characterized in that, The drying process described in step one (3) involves maintaining the temperature at 60–100 °C for 6–12 h.

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