A three-way catalyst for automobiles and a method for producing the same

Abstract

The application relates to the field of tail gas treatment, in particular to a three-way catalyst for automobiles and a preparation method thereof. The three-way catalyst for automobiles is coated on a honeycomb carrier to form a coating layer, and comprises a bottom anchoring layer, a functional catalytic layer and a surface protective layer; the bottom anchoring layer comprises, in percentage by weight, 60-70% of modified silica sol, 15-20% of lanthanum aluminate fiber, 10-15% of gamma-Al2O3 and 3-5% of nano silicon carbide; the functional catalytic layer comprises, in percentage by weight, 0.2-0.7% of noble metal active components, 2-5% of rare earth stabilizers, 1-3% of anti-poisoning additives and the balance of composite carriers; and the surface protective layer comprises, in percentage by weight, 60-70% of silicate glass powder, 20-25% of cerium oxide powder, 5-10% of ammonium bicarbonate and 3-5% of praseodymium oxide. The three-way catalyst has strong adhesion, high heat resistance and stability, excellent anti-poisoning property and controllable cost.

Description

Technical Field

[0001] This application relates to the field of exhaust gas treatment, and in particular to a three-way catalyst for automobiles and its preparation method. Background Technology

[0002] The three-way catalytic converter reduces CO, HC, and NO in gasoline engine exhaust. x The key component for the three pollutants is a catalyst coating on a honeycomb ceramic or metal support, containing precious metals (Pt, Pd, Rh) and oxygen storage materials (such as CeZrO). The performance and lifespan of this coating directly determine the efficiency and service life of the catalyst.

[0003] Existing three-way catalyst technologies generally suffer from the following bottlenecks: First, insufficient adhesion between the coating and the ceramic support. Traditional catalysts often use a single inorganic binder (such as silica sol or alumina sol), adhering to the support surface only through physical adsorption. Under the high temperatures (600-1000℃), vibration, and thermal cycling conditions during vehicle operation, the coating is prone to peeling and cracking, leading to the loss of catalytic active sites and a sharp decline in purification efficiency. Second, poor high-temperature stability. Noble metal active components (Pt, Pd, Rh) are prone to migration and aggregation in high-temperature environments, resulting in a reduction in active sites. At the same time, the support material is prone to sintering, reducing the specific surface area and further accelerating catalyst aging. Third, limited resistance to poisoning. Sulfur and phosphorus compounds in exhaust gas, as well as fuel additive residues, easily combine with active components to form inert substances, leading to catalyst poisoning and deactivation. Fourth, the coating structure is too simple, failing to simultaneously achieve adhesion, catalytic activity, and corrosion resistance, making it difficult to adapt to long-term and complex operating conditions.

[0004] To address these issues, existing technologies often improve performance by optimizing the type of binder or increasing the content of active components. However, single-dimensional optimization cannot achieve synergistic performance enhancement. For example, some solutions use organic-inorganic composite binders to improve adhesion, but the organic components are prone to decomposition at high temperatures, leading to abnormal coating porosity. Other solutions increase the amount of precious metals to delay activity decay, but this significantly increases production costs and cannot fundamentally solve the sintering and poisoning problems. Therefore, developing a ternary catalyst that combines strong adhesion, high thermal stability, excellent resistance to poisoning, and controllable cost has become a pressing technical challenge for the industry. Summary of the Invention

[0005] To improve adhesion and heat resistance, this application provides a three-way catalyst for automobiles and a method for preparing the same.

[0006] In the first aspect, this application provides a three-way catalyst for automobiles, employing the following technical solution:

[0007] A three-way catalyst for automobiles is coated onto a honeycomb carrier to form a coating, which includes a bottom anchoring layer, a functional catalytic layer and a surface protective layer.

[0008] The underlying anchoring layer comprises, by weight percentage: 60-70% modified silica sol and 15-20% lanthanum aluminate fiber. 10-15%, nano-silicon carbide 3-5%;

[0009] The functional catalytic layer comprises, by weight percentage: 0.2-0.7% precious metal active component, 2-5% rare earth stabilizer, 1-3% anti-poisoning agent, and the balance being a composite carrier;

[0010] The surface protective layer comprises, by weight percentage: 60-70% aluminosilicate glass powder, 20-25% cerium oxide micro powder, 5-10% ammonium bicarbonate, and 3-5% praseodymium oxide.

[0011] By adopting the above technical solution, this application employs a three-layer functionally graded coating structure. The bottom anchoring layer is mainly composed of modified silica sol, which forms chemical bonds with the carrier surface through a silane coupling agent. Combined with the three-dimensional network reinforcement of lanthanum aluminate fibers and the thermal conductivity regulation of nano-silicon carbide, it fundamentally improves the adhesion and thermal shock resistance of the coating under high-temperature vibration. The functional catalytic layer combines the synergistic ratio of noble metals Pt, Pd, and Rh with the high specific surface area and oxygen storage capacity of the composite carrier. Under the dual effects of rare earth stabilizers inhibiting carrier sintering and anti-poisoning agents preferentially adsorbing poisons, it achieves efficient catalysis and long-term stability. The surface protective layer utilizes the high-temperature melting characteristics of aluminosilicate glass powder to form a dense cover. Cerium oxide oxygen storage assists and ammonium bicarbonate pore-forming work synergistically. Under the stabilizing effect of praseodymium oxide, a protective layer with anti-corrosion, heat insulation, and gas diffusion capabilities is constructed. This structural design system solves the problems of weak adhesion, easy sintering at high temperatures, and poor resistance to poisoning of traditional catalysts, and comprehensively improves the durability and environmental adaptability of the catalyst.

[0012] Furthermore, the modified silica sol is an aminopropyltriethoxysilane modified silica sol.

[0013] By adopting the above technical solution, the silane coupling agent can form Si-O-Si covalent bonds with the carrier surface after hydrolysis. Its organic amino end further interacts with the coating components, realizing the transformation from physical adsorption to chemical bonding, which significantly enhances the bonding strength between the coating and the carrier under high temperature vibration and prevents peeling.

[0014] Furthermore, the lanthanum aluminate fiber has a diameter of 50-100 nm and a length of 5-10 μm.

[0015] By adopting the above technical solution, nanofibers form a three-dimensional network structure in the coating, which improves the mechanical strength of the coating through fiber toughening and crack deflection mechanism. Its low coefficient of thermal expansion and high melting point characteristics can effectively buffer thermal stress and inhibit the coating from cracking during thermal cycling.

[0016] Furthermore, the precious metal active component is a mixture of platinum, palladium, and rhodium, with a weight ratio of platinum:palladium:rhodium = (2-5):(4-10):(1-2.7).

[0017] By adopting the above technical solution, this formulation is based on Pt to NO. x Reduction, Pd oxidation of CO / HC and Rh oxidation of NO x The catalytic properties of decomposition are optimized, and the air-fuel ratio window is widened through the synergistic effect of ternary metals. This reduces the total amount of precious metals used while ensuring high conversion efficiency, thus achieving a balance between cost and performance.

[0018] Furthermore, the composite carrier is a mixture of γ-Al2O3 and cerium dioxide-zirconia solid solution, with a weight ratio of γ-Al2O3: cerium dioxide-zirconia solid solution = (2-3): (1-2).

[0019] By adopting the above technical solution, γ-Al2O3 provides a high specific surface area to disperse noble metals, and CeO2-ZrO2 solid solution regulates the local oxygen concentration through reversible oxygen storage. The two work together to enhance the dynamic response capability of the catalytic reaction, while the solid solution structure inhibits the Al2O3 phase transformation and noble metal migration at high temperature.

[0020] Furthermore, the rare earth stabilizer is a mixture of lanthanum oxide and yttrium oxide in a weight ratio of (1-2):1; the anti-poisoning auxiliary is a mixture of barium oxide and strontium oxide in a weight ratio of (1-3):1.

[0021] By adopting the above technical solutions, La₂O₃ and Y₂O₃ can be inserted into the Al₂O₃ lattice to suppress the θ phase transition and maintain the high-temperature specific surface area of ​​the support; BaO and SrO, due to their stronger basicity than noble metals, preferentially react with SO₂. x PO x They combine with acidic toxins to form stable salts, protecting active sites from permanent poisoning.

[0022] Furthermore, the cerium oxide micropowder has a particle size of 1-3 μm.

[0023] By adopting the above technical solution, CeO2 with appropriate particle size can form a uniform and dense layer on the surface, which has both physical barrier and oxygen storage functions, and its surface oxygen vacancies assist NO. x The process involves reduction and suppression of excessive sintering of the surface glass phase at high temperatures, while maintaining gas permeability.

[0024] Secondly, this application provides a method for preparing a three-way catalyst for automobiles, employing the following technical solution:

[0025] A method for preparing a three-way catalytic converter for automobiles, characterized by comprising the following steps:

[0026] S1. Preparation and curing of the base slurry:

[0027] Add the bottom components to deionized water, ball mill for 2-3 hours until the particle size D90≤3μm, adjust the viscosity to 600-700mPa·s, after negative pressure impregnation coating, dry at 150℃ for 4 hours, and calcine at 550℃ for 3 hours.

[0028] S2. Preparation and curing of functional layer slurry:

[0029] The composite carrier, rare earth stabilizer, and anti-poisoning agent were ball-milled to a particle size D90≤5μm. The precious metal active component was added and stirred for 1-2 hours. The viscosity was adjusted to 700-800mPa·s. After positive pressure spraying, the coating was dried at 120℃ for 3 hours and calcined at 500℃ for 4 hours.

[0030] S3. Preparation and curing of surface slurry:

[0031] The surface components are dispersed at high speed for 40-50 minutes until the particle size D90≤2μm, the viscosity is adjusted to 400-500mPa·s, and after spraying, dried at 100℃ for 2 hours, calcined at 600℃ for 2 hours, and cooled to obtain the finished product.

[0032] By adopting the above technical solutions, this method achieves structural optimization of each functional layer through layered slurry particle size control, viscosity adjustment, and differentiated coating-heat treatment processes: the bottom layer is impregnated under negative pressure to enhance carrier wetting and anchoring, the functional layer is sprayed under positive pressure to ensure uniform distribution of active components, and the surface layer is rapidly fired at low temperature to form a porous protective structure; the overall process reduces thermal stress damage through slow heating and baking, ensuring coating integrity, interlayer interface bonding, and functional realization.

[0033] Furthermore, in step S1, the negative pressure impregnation pressure is -0.06 to -0.07 MPa, and the holding time is 10 to 15 minutes.

[0034] By adopting the above technical solution, moderate negative pressure promotes the slurry to penetrate deep into the carrier pores, and deep adhesion is achieved through capillary action and pressure penetration, forming a mechanically interlocked structure, laying the foundation for high adhesion from the coating stage.

[0035] Furthermore, the heating rate for each roasting step is ≤5℃ / min.

[0036] By adopting the above technical solution, the organic components are gradually decomposed and the inorganic particles are sintered in an orderly manner through slow heating, which avoids the coating from cracking, bubbling or loosening due to excessive volatilization, and ensures the compactness and stability of the microstructure of each layer.

[0037] In summary, this application has the following beneficial effects:

[0038] 1. Ultra-high adhesion and structural integrity: Through an innovative bottom anchoring layer design, the fundamental problem of easy coating peeling is solved, and the adhesion performance is improved by an order of magnitude;

[0039] 2. Excellent high-temperature durability: With the help of rare earth stabilizers and composite carriers in the functional layer, the activity decay at high temperatures is greatly suppressed, and the activity retention rate after thermal aging exceeds 94%;

[0040] 3. Strong resistance to poisoning: Through the synergy of anti-poisoning agents and stabilization design, the catalyst's tolerance to poisons such as sulfur is significantly improved, with an activity decrease rate of less than 4.2%;

[0041] 4. High efficiency and broad catalytic activity: The three-layer functional design and optimized ratio ensure that the catalyst maintains leading three-way conversion efficiency (>97.5%@500℃) in the range of 400-600℃. Detailed Implementation

[0042] The present application will be further described in detail below with reference to the embodiments.

[0043] Example of raw material and intermediate preparation

[0044] raw material

[0045] It should be noted that: in the following examples, unless otherwise specified, the conditions shall be in accordance with conventional conditions or the manufacturer's recommended conditions; and the raw materials used in the following examples, unless otherwise specified, shall be from commercially available sources.

[0046] Underlying anchoring layer material:

[0047] Alkaline silica sol: specifications include 30% SiO2 content, 10-20 nm particle size, and pH 9-10;

[0048] Aminopropyltriethoxysilane (KH-550): Chemically pure, ≥ 98%;

[0049] γ-alumina ( Specifications: Specific surface area ≥ 150 m² 2 / g, particle size D50: 1-5 μm;

[0050] Nano-silicon carbide: specifications include a purity of ≥ 99% and an average particle size of 50 nm;

[0051] Functional catalyst layer raw materials:

[0052] Cerium dioxide-zirconia solid solution: with a CeO2:ZrO2 ratio of 3:2 (mol ratio) and a specific surface area ≥ 80 m². 2 / g;

[0053] Lanthanum oxide (La2O3): Specifications include purity ≥ 99.99% and particle size 1-3 μm;

[0054] Yttrium oxide (Y2O3): Specifications include purity ≥ 99.99% and particle size 1-3 μm;

[0055] Barium oxide (BaO): Purity ≥ 99.5%;

[0056] Strontium oxide (SrO): Purity ≥ 99.5%;

[0057] Surface protective layer raw materials:

[0058] Aluminosilicate glass powder: specifications include a softening point of 650-750℃ and a particle size D90 ≤ 5 μm;

[0059] Cerium oxide (CeO2) micro powder: purity ≥ 99.9%;

[0060] Ammonium bicarbonate (NH4HCO3): Analytical grade, ≥ 99.5%;

[0061] Praseodymium oxide (Pr6O) 11 Specifications: purity ≥ 99.5%, particle size 1-3 μm.

[0062] Preparation Example

[0063] Preparation Example 1

[0064] A modified silica sol, the preparation method of which is as follows:

[0065] 1) Pretreatment: Silica sol dilution and pH adjustment

[0066] 100 g of alkaline silica sol was added to a reaction vessel equipped with a stirrer. At room temperature and a stirring rate of 300 r / min, 35 g of anhydrous ethanol was slowly added and stirred for 15 minutes to obtain a uniformly diluted silica sol solution. Then, glacial acetic acid was added dropwise to adjust the pH of the solution to 4-5, and stirring was continued for 10 minutes to activate the hydroxyl groups on the surface of the silica sol particles.

[0067] 2) Silane hydrolysis: KH-550 pretreatment

[0068] 6g of aminopropyltriethoxysilane (KH-550) was mixed with 12g of deionized water and magnetically stirred at 25°C for 20 minutes to partially hydrolyze the ethoxy groups on the KH-550 molecular chain to generate active silanol groups, thus obtaining a hydrolyzed silane solution.

[0069] 3) Grafting reaction: Synthesis of modified silica sol

[0070] The hydrolyzed silane solution was slowly added dropwise to the pretreated silica sol solution at a rate of 1 mL / min. After the addition was complete, the temperature was raised to 50 °C, and the stirring rate was maintained at 300 r / min for 2.5 hours. During this process, the silanol groups generated by the hydrolysis of KH-550 undergo dehydration condensation with the hydroxyl groups on the surface of the silica sol particles, achieving the grafting of amino groups.

[0071] 4) Post-processing: purification and concentration

[0072] After the reaction was completed, the system was cooled to 25°C, and the pH was adjusted to 7-8 with 30% sodium hydroxide solution to terminate the reaction. Then, the system was distilled under vacuum of -0.08 MPa and 60°C to remove anhydrous ethanol and excess water until the silica sol solid content reached 20-22%, thus obtaining the aminopropyltriethoxysilane modified silica sol product.

[0073] Example

[0074] Example 1

[0075] A three-way catalyst for automobiles, the preparation method of which is as follows:

[0076] S0. Ceramic substrate pretreatment:

[0077] A cordierite honeycomb ceramic carrier (cordierite material, pore density 400cpsi) with a specification of φ100mm×120mm was placed in an 8% dilute nitric acid solution and soaked at 70℃ for 40 minutes. After being removed, it was rinsed with deionized water until pH=7, dried at 120℃ for 3 hours, and then calcined at 250℃ for 2 hours to activate the hydroxyl groups on the carrier surface and enhance its binding ability with the underlying layer.

[0078] S1. Preparation and curing of the base slurry:

[0079] According to the proportions in Table 1, weigh the modified silica sol, lanthanum aluminate fiber, γ-Al2O3, and nano silicon carbide, add deionized water, and ball mill in a planetary ball mill at 300 r / min for 2.5 hours. Control the slurry particle size D90≤3μm and adjust the viscosity to 600-700mPa·s to obtain the bottom anchoring layer slurry.

[0080] Using the negative pressure impregnation method, the pretreated ceramic carrier is placed in the above-mentioned bottom slurry, and a negative pressure of -0.06MPa is applied and maintained for 12 minutes to allow the slurry to fully penetrate into the carrier pores. After removal, the excess slurry is blown away with compressed air (0.3MPa) until the carrier increases in weight by 30g. It is then dried at 150℃ for 4 hours, and then heated to 550℃ at a rate of 5℃ / min and calcined for 3 hours to complete the bottom layer curing.

[0081] S2. Preparation and curing of functional layer slurry:

[0082] According to the proportions in Table 1, γ-Al₂O₃, cerium dioxide-zirconia solid solution (Ce:Zr=3:2), lanthanum oxide, yttrium oxide, barium oxide, and strontium oxide were taken, and deionized water was added. The mixture was ball-milled for 3 hours until the particle size D90 ≤ 5 μm to obtain a mixed support slurry. Platinum precursor solution, palladium precursor solution, and rhodium precursor solution were added, and the mixture was stirred for 1.5 hours to ensure uniform loading of the noble metals. An appropriate amount of deionized water was added to adjust the slurry viscosity to 750 mPa·s to obtain the functional catalyst layer slurry.

[0083] The functional layer slurry was sprayed onto the cured substrate surface using a positive pressure spraying method. The amount of spraying was controlled to increase the carrier weight by an additional 80g. The substrate was dried at 120℃ for 3 hours, then heated to 500℃ at a rate of 4℃ / min and calcined for 4 hours to complete the curing of the functional layer.

[0084] S3. Preparation and curing of surface slurry:

[0085] According to the proportions in Table 1, take aluminosilicate glass powder, cerium oxide micro powder, ammonium bicarbonate and praseodymium oxide, add deionized water, disperse at high speed for 40 minutes, control the slurry particle size D90≤2μm, and adjust the viscosity to 450mPa·s to obtain the surface protective layer slurry.

[0086] The surface slurry was sprayed onto the functional layer surface, and the spraying amount was controlled to increase the carrier weight by 20g. It was then dried at 100℃ for 2 hours. During this drying process, ammonium bicarbonate decomposed upon heating, generating gas that formed an initial porous structure within the coating. Subsequently, the temperature was increased to 600℃ at a rate of 5℃ / min and calcined for 2 hours to soften and sinter the aluminosilicate glass powder, fixing and optimizing the aforementioned porous structure. Simultaneously, the surface layer was strengthened and densified. After cooling, the finished ternary catalyst was obtained.

[0087] Table 1 Raw Material Proportions (g)

[0088]

[0089] The modified silica sol was aminopropyltriethoxysilane modified silica sol, derived from Preparation Example 1; lanthanum aluminate fibers had a diameter of 70 nm and a length of 8 μm; cerium oxide microparticles had a particle size of 2 μm; the amount of noble metal precursor solution in the functional catalyst layer was as follows: 0.1 g of Pt corresponds to 10 mL of 10 g / L chloroplatinic acid solution, 0.2 g of Pd corresponds to 10 mL of 20 g / L palladium nitrate solution, and 0.05 g of Rh corresponds to 10 mL of 5 g / L rhodium nitrate solution. Other examples were calculated based on the mass of the noble metals.

[0090] Example 4

[0091] Unlike Example 1, in Example 4, the weight ratio of platinum (added in the form of chloroplatinic acid), palladium (added in the form of palladium nitrate), and rhodium (added in the form of rhodium nitrate) is 5:10:2.7.

[0092] Example 5

[0093] Unlike Example 1, in Example 5, the weight ratio of platinum (added in the form of chloroplatinic acid), palladium (added in the form of palladium nitrate), and rhodium (added in the form of rhodium nitrate) is 3:7:2.

[0094] Example 6

[0095] Unlike Example 1, in Example 6 the weight ratio of γ-Al2O3:cerium dioxide-zirconia solid solution in the composite carrier is 2:1.

[0096] Example 7

[0097] Unlike Example 1, in Example 7, the weight ratio of γ-Al2O3:cerium dioxide-zirconia solid solution in the composite carrier is 1:2.

[0098] Example 8

[0099] Unlike Example 1, in Example 8, the weight ratio of lanthanum oxide to yttrium oxide in the rare earth stabilizer is 2:1.

[0100] Comparative Example

[0101] Comparative Example 1

[0102] Unlike Example 1, Comparative Example 1 includes a single-functional coating: 30g of ordinary silica sol, 48g of γ-Al₂O₃, and 32g of Ce-Zr solid solution. 1.5g, Y2O3 1.5g, BaO 0.8g, SrO 0.8g, Pt 0.1g, Pd 0.2g, Rh 0.05g, deionized water 220g, deionized water for viscosity adjustment 15g; Preparation steps: S1. Ceramic carrier pretreatment is the same as in Example 1; S2. Single coating slurry preparation: Mix all components, ball mill for 3 hours until D90≤5μm, adjust viscosity to 750mPa·s; S3. Positive pressure spray coating, control carrier weight gain to 130g; S4. Dry at 120℃ for 3 hours, calcine at 500℃ for 4 hours, cool to obtain the finished product.

[0103] Comparative Example 2

[0104] Unlike Example 1, in Comparative Example 2, the bottom layer does not use the synergistic system of modified silica sol and lanthanum aluminate fiber, but instead uses ordinary silica sol without lanthanum aluminate fiber; the proportions of other components remain unchanged; the bottom anchoring layer consists of 65g of ordinary silica sol, 12g of γ-Al2O3, 4g of nano silicon carbide, and 150g of deionized water.

[0105] Comparative Example 3

[0106] Unlike Example 1, Comparative Example 3 did not contain rare earth stabilizers in the functional layer, and the proportions of other components remained unchanged; the functional catalyst layer consisted of 48g of γ-Al2O3, 32g of Ce-Zr solid solution, 0.8g of BaO, 0.8g of SrO, 0.1g of Pt, 0.2g of Pd, 0.05g of Rh, 200g of deionized water, and 12g of deionized water for viscosity adjustment.

[0107] Performance testing

[0108] 1. Catalytic activity test (three-way conversion efficiency, %)

[0109] Simulating actual operating conditions on an engine test bench, with the air-fuel ratio controlled near the theoretical value (λ=1), the catalyst was tested at three characteristic temperatures: 400℃, 500℃, and 600℃, to control the emissions of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). The conversion efficiency of ) is shown in Table 2.

[0110] 2. Coating adhesion test

[0111] The ultrasonic peeling method was used to measure the coating mass loss rate (%) and evaluate the bonding strength. The results are shown in Table 3.

[0112] 3. Catalytic activity retention rate after thermal aging

[0113] After static aging at 1000℃ for 24h, the retention rate (%) of the triple-effect conversion efficiency at 500℃ was tested, and the results are shown in Table 3.

[0114] 4. Sulfur poisoning resistance test

[0115] Containing 50ppm After running in the exhaust gas for 100 hours, the decrease in catalytic activity (%) was tested, and the results are shown in Table 3.

[0116] 5. Microstructure observation (SEM)

[0117] The coating uniformity, porosity, and interlayer bonding were evaluated, and the results are shown in Table 3.

[0118] Table 2. Catalytic activity detection results

[0119]

[0120] Table 3 Results of Physical and Durability Tests

[0121]

[0122] As shown in Table 2, within a wide temperature window of 400℃, 500℃, and 600℃, all examples (1-8) showed good results regarding CO, HC, and other pollutants. The conversion efficiency of the examples was significantly better than that of the three comparative examples. At a typical operating temperature of 500°C, the catalytic activity of the examples was generally above 97.5%, reaching a maximum of 99.5%. In contrast, the catalytic activity of Comparative Example 1 was only 93.5%-96.8%, Comparative Example 2 was 95.2%-97.5%, and Comparative Example 3 was 95.8%-97.8%. This directly proves that the synergistic effect of the "three-layer gradient structure" and "optimized ratio of precious metals and composite support" proposed in this application can significantly improve the core purification capacity of the catalyst throughout the entire operating temperature range, achieving high and stable catalytic efficiency.

[0123] As shown in Table 3, the adhesion loss rate of all embodiments was less than 1.3%, demonstrating excellent bonding strength. In contrast, the loss rate of Comparative Example 1 was as high as 12.5%, and that of Comparative Example 2 was 8.6%. This difference of more than an order of magnitude strongly verifies the success of the underlying anchoring layer design. The chemical bonding provided by the modified silica sol, combined with the three-dimensional network reinforcement effect formed by the lanthanum aluminate fibers, fundamentally solves the industry problem of traditional catalyst coatings being prone to detachment and cracking under high temperature vibration, laying the foundation for the long life of the catalyst.

[0124] As shown in Table 3, after harsh aging at 1000℃ for 24 hours, the activity retention rates of the examples were all above 94.5%, reaching a maximum of 97.0%, while the retention rate of Comparative Example 1 plummeted to 78.4%, and Comparative Example 3 was only 82.7%. This comparison clearly demonstrates the indispensability of rare earth stabilizers (lanthanum oxide / yttrium oxide). They effectively inhibit the activity of the support ( The phase transformation and sintering at high temperatures maintain a high specific surface area, thereby preventing the migration and aggregation of the noble metal active components. The three-layer structure and component design of this application endow the catalyst with excellent resistance to high-temperature aging.

[0125] As shown in Table 3, after simulating sulfur poisoning, the catalytic activity of the examples decreased by less than 4.2%, demonstrating excellent resistance to poisoning. In contrast, the comparative examples showed a decrease of 18.6% in Comparative Example 1 and the largest decrease of 20.5% in Comparative Example 3. This verifies the synergistic protective mechanism of the anti-poisoning agent (barium oxide / strontium oxide) and the rare earth stabilizer. The alkaline agent preferentially adsorbs acidic poisons, while the stable support structure avoids accelerated sintering caused by poisoning. At the same time, the surface protective layer also plays a role in physically isolating some of the poisons. Therefore, the catalyst of this application exhibits strong environmental adaptability and service life guarantee.

[0126] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A three-way catalyst for automobiles, wherein a coating is formed by coating a honeycomb carrier, characterized in that, It includes a bottom anchoring layer, a functional catalytic layer, and a surface protective layer; The bottom anchoring layer comprises, by weight percentage: 60-70% modified silica sol, 15-20% lanthanum aluminate fiber, 10-15% γ-Al2O3, and 3-5% nano-silicon carbide; The functional catalytic layer comprises, by weight percentage: 0.2-0.7% precious metal active component, 2-5% rare earth stabilizer, 1-3% anti-poisoning agent, and the balance being a composite carrier; The surface protective layer comprises, by weight percentage: 60-70% aluminosilicate glass powder, 20-25% cerium oxide micro powder, 5-10% ammonium bicarbonate, and 3-5% praseodymium oxide.

2. The three-way catalytic converter for automobiles according to claim 1, characterized in that, The modified silica sol is an aminopropyltriethoxysilane modified silica sol.

3. The three-way catalytic converter for automobiles according to claim 1, characterized in that, The lanthanum aluminate fiber has a diameter of 50-100 nm and a length of 5-10 μm.

4. The three-way catalytic converter for automobiles according to claim 1, characterized in that, The precious metal active component is a mixture of platinum, palladium and rhodium, with a weight ratio of platinum:palladium:rhodium = (2-5):(4-10):(1-2.7).

5. A three-way catalytic converter for automobiles according to claim 1, characterized in that, The composite carrier is a mixture of γ-Al2O3 and cerium dioxide-zirconia solid solution, with a weight ratio of γ-Al2O3: cerium dioxide-zirconia solid solution = (2-3): (1-2).

6. A three-way catalytic converter for automobiles according to claim 1, characterized in that, The rare earth stabilizer is a mixture of lanthanum oxide and yttrium oxide in a weight ratio of (1-2):1; the anti-poisoning adjuvant is a mixture of barium oxide and strontium oxide in a weight ratio of (1-3):

1.

7. A three-way catalytic converter for automobiles according to claim 1, characterized in that, The cerium oxide micro powder has a particle size of 1-3 μm.

8. A method for preparing a three-way catalytic converter for automobiles as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Preparation and curing of the base slurry: Add the bottom components to deionized water, ball mill for 2-3 hours until the particle size D90≤3μm, adjust the viscosity to 600-700mPa·s, after negative pressure impregnation coating, dry at 150℃ for 4 hours, and calcine at 550℃ for 3 hours. S2. Preparation and curing of functional layer slurry: The composite carrier, rare earth stabilizer, and anti-poisoning agent were ball-milled to a particle size D90≤5μm. The precious metal active component was added and stirred for 1-2 hours. The viscosity was adjusted to 700-800mPa·s. After positive pressure spraying, the coating was dried at 120℃ for 3 hours and calcined at 500℃ for 4 hours. S3. Preparation and curing of surface slurry: The surface components are dispersed at high speed for 40-50 minutes until the particle size D90≤2μm, the viscosity is adjusted to 400-500mPa·s, and after spraying, dried at 100℃ for 2 hours, calcined at 600℃ for 2 hours, and cooled to obtain the finished product.

9. The method for preparing a three-way catalyst for automobiles according to claim 8, characterized in that, In step S1, the negative pressure impregnation pressure is -0.06 to -0.07 MPa, and the holding time is 10 to 15 minutes.

10. The method for preparing a three-way catalyst for automobiles according to claim 8, characterized in that, The heating rate for each roasting step is ≤5℃ / min.

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