Automobile exhaust treatment catalyst and preparation method thereof

Abstract

The invention discloses an automobile exhaust treatment catalyst and a preparation method thereof, the automobile exhaust treatment catalyst is composed of a matrix and an active coating coated on the surface of the matrix, the active coating comprises an upper Pd-Rh coating and a lower Pd coating, the upper Pd-Rh coating is prepared from Rh second cerium-zirconium composite oxide uniformly coated with phosphorus and aluminum P2O5-Al2O3, Pd-loaded lanthanum aluminum oxide, an auxiliary agent and an adhesive, and the lower Pd-Rh coating is prepared from Rh second cerium-zirconium composite oxide uniformly coated with phosphorus and aluminum P2O5-Al2O3. The mass ratio of P2O5-Al2O3 to the second cerium-zirconium-rare earth oxygen storage material is (1: 50)-(1: 10); the Rh second cerium-zirconium rare earth oxygen storage material uniformly coated with phosphorus and aluminum P2O5-Al2O3 is obtained by enriching the Rh element on the surface layer of second cerium-zirconium composite oxide particles and uniformly coating the particles with a layer of porous P2O5-Al2O3 compound. The lower Pd coating is prepared from lanthanum modified aluminum oxide La2O3-Al2O3 loaded with Pd, a first cerium-zirconium-rare earth oxygen storage material loaded with Pd, an auxiliary agent and an adhesive, and the auxiliary agent is alkaline earth metal salt. The catalyst can inhibit high-temperature sintering of Rh, migration into aluminum oxide crystal lattices and maintain the oxygen storage performance of the cerium-zirconium carrier, and can maintain high catalytic activity under the condition of low precious metal dosage after severe aging.

Description

Technical Field

[0001] This invention relates to the field of automotive exhaust gas treatment catalysts, and more specifically to an automotive exhaust gas treatment catalyst and its preparation method. Background Technology

[0002] In the widely used Pd-Rh three-way catalyst system, the Rh component is crucial for the efficient reduction of NOx, but its anti-aging performance is a weak point in the system. In existing technologies, Rh supports face the following dilemma: Although activated alumina supports possess high specific surface area and excellent mass transfer performance, at temperatures above 600℃, Rh... 3+ Rh can migrate into the alumina (Al2O3) lattice to form inactive rhodium aluminate, leading to permanent catalyst deactivation [Cao, Y., et al.. Improved activity and durability of Rh-based three-way catalyst underdiverse aging atmospheres by ZrO2 support[J].Environ. Sci. (2016).]. Although some authors have directly modified γ-Al2O3 with phosphorus [Masato Machida, et al..AlPO4 as a Support Capable of Minimizing Threshold Loading of Rh in Automotive Catalysts[J].Chem. Mater.(2009).] or Chinese patent document CN112316961B uses P-La-Zr-AlO composite oxides as a support to inhibit the formation of rhodium aluminate from Rh and alumina and improve thermal stability, they cannot provide oxygen storage performance and are difficult to meet the requirements of China VI standard for efficient purification within the dynamic air-fuel ratio window.

[0003] Patent WO2008 / 054026, CN106000397 A uses high zirconium / yttrium stabilized zirconium oxide as the carrier. Although it exhibits good initial activity and nitrogen oxide (NOx) storage performance, its specific surface area is low and it inherently lacks oxygen storage capacity. At high temperatures, it still suffers from metal sintering and carrier instability, making it difficult to meet the requirements of China VI standard for efficient purification within the dynamic air-fuel ratio window.

[0004] Patent CN105536782 A uses cerium-zirconium composite oxide as a carrier, which can provide a certain oxygen storage capacity, but there are still problems of oxygen storage performance deterioration and loss of active centers at high temperatures.

[0005] In summary, existing technologies cannot simultaneously ensure the stability of Rh and the oxygen storage capacity of the Rh-loaded carrier after high-temperature aging. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide an automotive exhaust gas treatment catalyst and its preparation method. This catalyst can inhibit Rh high-temperature sintering and migration into the alumina lattice, maintain the oxygen storage performance of the cerium-zirconium support, and maintain high catalytic activity with low amounts of precious metals after harsh aging.

[0007] This invention is achieved through the following technical solution: An automotive exhaust gas treatment catalyst comprises a substrate and an active coating applied to the surface of the substrate. The active coating includes an upper Pd-Rh coating and a lower Pd coating. The upper Pd-Rh coating is made of Rh second cerium-zirconium composite oxide uniformly coated with phosphorus aluminum P2O5-Al2O3, Pd-loaded lanthanum alumina, additives, and a binder. The mass ratio of P2O5-Al2O3 to the second cerium-zirconium rare earth oxygen storage material is 1:50 to 1:10. The phosphorus aluminum P2O5-Al2O3 uniformly coated Rh second cerium-zirconium rare earth oxygen storage material is obtained by enriching Rh elements on the surface of second cerium-zirconium composite oxide particles and uniformly coating them with a porous P2O5-Al2O3 composite.

[0008] The preparation method of Rh second cerium zirconium rare earth oxygen storage material uniformly coated with phosphorus aluminum P2O5-Al2O3 is as follows: the phosphorus aluminum precursor is uniformly coated on the surface of the second cerium zirconium composite oxide particles enriched with Rh element by urea slow-release homogeneous precipitation. The Rh element enrichment on the surface of the second cerium zirconium composite oxide particles is specifically obtained by impregnating the second cerium zirconium composite oxide particles with an Rh salt solution containing organic alkali.

[0009] The organic base is one or more of ethylenediamine, 1,3-propanediamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylethylammonium hydroxide, or dimethyldiethylammonium hydroxide.

[0010] The lower Pd coating is made of Pd-loaded lanthanum alumina La2O3-Al2O3, Pd-loaded first cerium zirconium rare earth oxygen storage material, additives, and binders. The additives are alkaline earth metal salts.

[0011] Lanthanum alumina La2O3-Al2O3 is lanthanum-modified gamma alumina γ-Al2O3 with a La2O3 content of 0~25%, and the La2O3 content is not 0.

[0012] Both the first and second cerium-zirconium rare-earth oxygen storage materials are cerium-zirconium solid solutions. Both materials are lanthanum, praseodymium, neodymium, or yttrium-modified cerium-zirconium solid solutions. The cerium dioxide (CeO2) content in the first material is 30–85 wt%, while the CeO2 content in the second material is 10–50 wt%.

[0013] The mass ratio of the Pd-loaded La2O3-Al2O3 material to the first cerium-zirconium rare earth oxygen storage material is 1:10 to 10:1, and the mass ratio of the P2O5-Al2O3-coated Rh second cerium-zirconium rare earth oxygen storage material to the Pd-loaded lanthanum alumina is 5:1 to 1:5.

[0014] A method for preparing an automotive exhaust gas treatment catalyst as described above includes sequentially coating an upper Pd-Rh coating and a lower Pd coating on a substrate from bottom to top. The preparation of the upper Pd-Rh coating specifically includes: 1) impregnating a second cerium-zirconium rare earth oxygen storage material with an Rh salt solution to obtain a Rh second cerium-zirconium rare earth oxygen storage material with Rh enriched on the surface of the second cerium-zirconium rare earth oxygen storage material; 2) uniformly precipitating and coating phosphorus and aluminum onto the Rh second cerium-zirconium rare earth oxygen storage material using an aluminum salt solution, a phosphate solution, and a urea solution via a "urea slow-release homogeneous precipitation method"; 3) forming a coating by uniformly coating the phosphorus-aluminum (P2O5-Al2O3) Rh second cerium-zirconium composite oxide, Pd-loaded lanthanum alumina, additives, and a binder.

[0015] The adhesive is one or more of aluminum sol, silica sol, and zirconium sol, preferably aluminum sol.

[0016] Specifically, a method for preparing an automotive exhaust gas treatment catalyst includes the following steps: S1. Pure water is added to the Pd noble metal salt solution and stirred evenly to obtain a mixed solution. The mixed solution is impregnated onto La2O3-Al2O3 and the first cerium-zirconium rare earth oxygen storage material using the equal volume impregnation method. After standing for 1 hour, it is pre-dried at 100-150℃ for 2-4 hours and calcined at 500-600℃ for 2 hours to obtain Pd-containing catalyst powder A1.

[0017] S2. The catalyst powder A1, binder, additives and pure water prepared in S1 are ball-milled together to obtain a first mixed slurry. The first mixed slurry is then coated onto the substrate and dried and calcined to obtain a lower Pd coating.

[0018] S3. Add pure water to the Pd noble metal salt solution and stir evenly to obtain a mixed solution. Use the equal volume impregnation method to impregnate the mixed solution onto La2O3-Al2O3. After standing for 1 hour, pre-dry at 100-150℃ for 2-4 hours and calcine at 500-600℃ for 2 hours to obtain Pd-containing catalyst powder B1.

[0019] Rh precious metal salt solution and organic base are added to pure water and stirred evenly to obtain a mixed solution. Then, the mixed solution is impregnated onto the second cerium zirconium rare earth oxygen storage material by the equal volume impregnation method. After standing for 1 hour, it is pre-dried at 100-150℃ for 2-4 hours and then calcined at 500-600℃ for 2 hours to obtain Rh-containing catalyst powder C1. Aluminum salt solution, phosphate solution, urea solution and pure water are mixed evenly to obtain a mixed solution, wherein the concentration of phosphorus aluminum precursor (P+Al) is controlled at 0.01-0.05 mol / L; pure water is added to powder C1, the solid content is controlled at 15%-45%, and after stirring evenly, it is placed in a water bath at 80-100℃ and the mixed solution is added dropwise, and then stirred for 0.5-6h. After filtration and washing, it is dried at 100-150℃ for 2-6h and calcined in air at 400-600℃ for 4h, with a heating rate ≤3°C / min, to obtain P2O5-Al2O3-coated Rh second cerium zirconium composite oxide C2 prepared by the "urea slow-release homogeneous precipitation" process.

[0020] S4. Mix and ball-mill the catalyst powder C2, catalyst powder B1, binder, additives and pure water prepared in S3 to obtain a second mixed slurry; coat the second mixed slurry onto the lower Pd coating layer, and obtain a Pd-Rh type catalyst after drying and calcination.

[0021] In steps S1 and S3, the Pd and Rh precious metal salt solutions are both soluble precious metal salt solutions, more specifically including ammonium salts, chloride salts, or nitrate salts; preferably nitrate salts.

[0022] In step S3, the organic base is one or more of ethylenediamine, 1,3-propanediamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylethylammonium hydroxide, or dimethyldiethylammonium hydroxide; preferably, tetramethylammonium hydroxide. The aluminum salt is one or more of aluminum nitrate, aluminum sulfate, or aluminum chloride; preferably, aluminum nitrate. The phosphate is one or more of phosphoric acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, potassium hydrogen phosphate, or potassium dihydrogen phosphate; preferably, phosphoric acid.

[0023] The first cerium-zirconium rare earth oxygen storage material and the second cerium-zirconium rare earth oxygen storage material in steps S1 and S3 can be cerium-zirconium solid solutions, or one or more modified cerium-zirconium solid solutions of lanthanum, praseodymium, neodymium, and yttrium; In steps S2 and S4, the additives are alkaline earth metal salts, preferably barium salts and strontium salts; The adhesive used in steps S2 and S4 is one or more of aluminum sol, silica sol, and zirconium sol, preferably aluminum sol.

[0024] In step S2, the amount of Pd used is 0.5–100 g / ft. 3 In step S4, the amount of Pd used is 0.5~100g / ft. 3 The dosage of Rh is 0.1~10g / ft. 3 .

[0025] The mass ratio of the Pd-loaded La2O3-Al2O3 material to the first cerium-zirconium rare earth oxygen storage material is 1:10 to 10:1. The mass ratio of the P2O5-Al2O3-coated Rh second cerium-zirconium composite oxide to the Pd-loaded lanthanum alumina is 1:5 to 5:1.

[0026] In step S3, the molar ratio of phosphorus aluminum precursor (P+Al) to urea is controlled to be 1:12-1:6, more preferably 1:10; the mass ratio of Rh to organic base is 1:50-1:5; and the mass ratio of Rh to phosphorus is 1:5-1:0.3.

[0027] The high-anti-aging catalyst of this invention possesses superior performance stemming from the unique structure of its core component, the "P2O5-Al2O3-coated Rh second cerium-zirconium composite oxide," in the upper Pd-Rh coating. This structure achieves efficient stabilization and protection of the Rh component through multiple mechanisms: First, an organic base is selected to regulate the loading of soluble Rh salt onto the second cerium-zirconium composite oxide, enriching the surface of the material with Rh. Then, aluminum and phosphorus are uniformly coated onto the surface of the Rh second cerium-zirconium composite oxide, forming a porous AlPO4 shell in situ on the Rh / cerium-zirconium surface and forming Rh-OP chemical bonds with Rh. This synergistic effect prevents the active sites from being buried, maintains a high specific surface area and pore connectivity, and fundamentally inhibits Rh sintering, migration, and rhodium aluminate formation. This effectively suppresses the thermal aging of the second cerium-zirconium oxygen storage material, providing the catalyst with high oxygen storage capacity. This offers significant advantages in catalyst durability testing, particularly in engines with large air-fuel ratio fluctuations. Meanwhile, when preparing the second mixed slurry, adding Pd supported by La2O3-Al2O3 with a large specific surface area can simultaneously improve the mass transfer performance and activity of the catalyst coating, thereby improving the catalyst's conversion performance of pollutants at high space velocities.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention overcomes the shortcomings of poor thermal stability and durability of Rh catalysts. Even with low amounts of precious metals, it maintains excellent CO, HC, and NOx purification activity and high oxygen storage capacity after harsh aging. It improves the catalyst's pollutant conversion performance under high space velocity and high air-fuel ratio fluctuations, significantly enhancing its thermal stability and service life. The catalyst exhibits a low NOx ignition temperature and good durability. This invention achieves "dual locking" of Rh active sites through a combination of "organic base-regulated surface distribution" and "urea slow-release construction of a uniform porous phosphorus-aluminum coating layer." Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings: Figure 1 The performance T of catalysts in Examples 1-5 and Comparative Examples 1-6 was compared. 50 Comparison chart; Figure 2 The performance T of catalysts in Examples 1-5 and Comparative Examples 1-6 was compared. 90 Comparison chart; Figure 3 The graph shows a comparison of the oxygen storage capacity of small-scale catalysts in Examples 1-5 and Comparative Examples 1-6.

[0030] Figure 4 This is a schematic diagram of the catalyst of the present invention.

[0031] Figure 5 The bench performance ignition temperature T for Examples 6 and 7 is... 50 Comparison chart.

[0032] Figure 6 This is a comparison chart of the oxygen storage capacity of the test bench in Example 6 and Comparative Example 7.

[0033] Figure 7 The image shows a comparison of CO emissions from vehicles after aging at 1050℃ for 20 hours in Example 6 and Comparative Example 7.

[0034] Figure 8 The image shows a comparison of THC emissions from vehicles after aging at 1050℃ for 20 hours in Example 6 and Comparative Example 7.

[0035] Figure 9 The image shows a comparison of NOx emissions from vehicles after aging at 1050℃ for 20 hours in Example 6 and Comparative Example 7.

[0036] Figure 10 This is a comparison chart showing the percentage emissions of CO, THC, and NOx after aging at 1050℃ for 20h for Example 6 and Comparative Example 7. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0038] The catalysts listed in the comparative examples and embodiments of this invention all have a two-layer structure, with a Pd coating on the lower layer and a Pd-Rh coating on the upper layer.

[0039] Comparative Example 1: S1. Add 100g of water to 0.25g of palladium nitrate solution and stir evenly to obtain a mixed solution. Using the equal volume impregnation method, impregnate the mixed solution onto 49.875g of La2O3-Al2O3 and 49.875g of first cerium zirconium rare earth oxygen storage material (of which CeO2 content is 45% and La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h, and then calcine at 500℃ for 2h to obtain the lower catalyst powder A1.

[0040] S2. 90g of lower layer catalyst powder A1, 5g of aluminum sol, 5g of barium carbonate, and 200g of pure water were ball-milled together to obtain a first mixed slurry. This first mixed slurry was then coated onto a honeycomb ceramic substrate with a diameter of 1 inch, a length of 1 inch, and a mesh size of 400 mesh at a concentration of 137.34g / L. After drying and calcination, a Pd content of 8.75g / ft was obtained. 3 The first catalyst.

[0041] S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain mixed solution A. Using the equal volume impregnation method, impregnate mixed solution A onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain upper catalyst powder B1.

[0042] 0.25g of rhodium nitrate solution was added to 50g of water and stirred evenly to obtain mixed solution B. Then, mixed solution B was impregnated onto 99.75g of second cerium zirconium rare earth oxygen storage material (with CeO2 content of 23%) using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C11.

[0043] S4. Mix 45g of catalyst powder C11, 45g of catalyst powder B1, 5g of aluminum sol, 5g of barium carbonate, and 200g of pure water and ball mill to obtain a second mixed slurry. Coat the second mixed slurry onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, obtain the final Pd-Rh type catalyst with a Pd content of 32.75g / ft. 3 The Rh content is 3g / ft 3 It was named Catalyst 1#.

[0044] Comparative Example 2: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain mixed solution A. Using the equal volume impregnation method, impregnate mixed solution A onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain upper catalyst powder B1.

[0045] 0.25g of rhodium nitrate solution and 2.5g of tetramethylammonium hydroxide were added to 50g of water and stirred evenly to obtain mixed solution B. Then, mixed solution B was impregnated onto 99.75g of second cerium zirconium rare earth oxygen storage material (with CeO2 content of 23%) using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C12.

[0046] S4. Mix and ball-mill 45g of catalyst powder C12, 45g of catalyst powder B1, 5g of aluminum sol, 5g of barium carbonate, and 200g of pure water to obtain a second mixed slurry. Coat the second mixed slurry onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, obtain the final Pd-Rh type catalyst with a Pd content of 32.75g / ft. 3 The Rh content is 3g / ft 3 It was named Catalyst 2#.

[0047] Comparative Example 3: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain mixed solution A. Using the equal volume impregnation method, impregnate mixed solution A onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain upper catalyst powder B1.

[0048] 0.25g of rhodium nitrate solution was added to 50g of water and stirred evenly to obtain mixed solution B. Then, mixed solution B was impregnated onto 96.53g of second cerium zirconium rare earth oxygen storage material (with CeO2 content of 23%) using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C13.

[0049] 3.06g of aluminum nitrate, 0.16g of phosphoric acid solution, and pure water were mixed evenly to obtain mixed solution C. Mixed solution C was impregnated onto 96.78g of powder C13 using the equal volume impregnation method. After stirring evenly, the mixture was allowed to stand for 1 hour, dried at 100℃ for 6 hours, and calcined in air at 500℃ for 4 hours with a heating rate of 2°C / min to obtain P2O5-Al2O3 coated Rh second cerium zirconium composite oxide C21.

[0050] S4. Mix and ball-mill 45g of catalyst powder C21, 45g of catalyst powder B1, 5g of aluminum sol, 5g of barium carbonate, and 200g of pure water to obtain a second mixed slurry; coat the second mixed slurry onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, obtain the final Pd-Rh type catalyst, wherein the Pd content is 32.75g / ft. 3 The Rh content is 3g / ft 3 It was named Catalyst 3#.

[0051] Comparative Example 4: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain mixed solution A. Using the equal volume impregnation method, impregnate mixed solution A onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain upper catalyst powder B1.

[0052] 0.25g of rhodium nitrate solution was added to 50g of water and stirred evenly to obtain mixed solution B. Then, mixed solution B was impregnated onto 99.75g of AlPO4 using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C22.

[0053] S4. Mix and ball-mill 45g of catalyst powder C22, 45g of catalyst powder B1, 5g of aluminum sol, 5g of barium carbonate, and 200g of pure water to obtain a second mixed slurry; coat the second mixed slurry onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, obtain the final Pd-Rh type catalyst, wherein the Pd content is 32.75g / ft. 3 The Rh content is 3g / ft3 It was named Catalyst 4#.

[0054] Comparative Example 5: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain mixed solution A. Using the equal volume impregnation method, impregnate mixed solution A onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain upper catalyst powder B1.

[0055] 0.25g of rhodium nitrate solution was added to 50g of water and stirred evenly to obtain mixed solution B. Then, mixed solution B was impregnated onto 99.75g of Y-ZrO2 using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C23.

[0056] S4. Mix and ball-mill 45g of catalyst powder C23, 45g of catalyst powder B1, 5g of aluminum sol, 5g of barium carbonate, and 200g of pure water to obtain a second mixed slurry; coat the second mixed slurry onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, obtain the final Pd-Rh type catalyst, wherein the Pd content is 32.75g / ft. 3 The Rh content is 3g / ft 3 It was named Catalyst 5#.

[0057] Comparative Example 6: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain mixed solution A. Using the equal volume impregnation method, impregnate mixed solution A onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain upper catalyst powder B1.

[0058] Dissolve 20g of lanthanum nitrate and 20g of zirconium nitrate in 60g of pure water, stir and mix evenly, and then impregnate the mixed solution onto 60g of γ-alumina using the initial wet impregnation method. After stirring evenly, let stand for 4h, pre-dry at 120℃ for 2h, and calcine at 1000℃ for 4h to obtain La-Zr-AlOx. 60g of pure water and 10g of H3PO4 were mixed to obtain H3PO4 solution. The H3PO4 solution was impregnated onto 90g of La-Zr-AlOx by the initial wet impregnation method. After stirring evenly, it was allowed to stand for 2h, pre-dried at 100℃ for 5h, and calcined at 900℃ for 4h to obtain P-La-Zr-AlOy. 0.25g of rhodium nitrate solution was added to 50g of water and stirred evenly to obtain mixed solution B. Then, mixed solution B was impregnated onto 99.75g of P-La-Zr-AlOy using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C24.

[0059] S4. Mix and ball-mill 45g of catalyst powder C24, 45g of catalyst powder B1, 5g of aluminum sol, 5g of barium carbonate, and 200g of pure water to obtain a second mixed slurry. Coat the second mixed slurry onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, obtain the final Pd-Rh type catalyst with a Pd content of 32.75g / ft. 3 The Rh content is 3g / ft 3 It was named Catalyst 6#.

[0060] Comparative Example 7: The preparation of the first mixed slurry was the same as in Comparative Example 1. The first mixed slurry was coated at a concentration of 137.34 g / L onto a honeycomb ceramic substrate with a diameter of 118.4 mm, a length of 127 mm, and a mesh size of 750. After drying and calcination, a Pd content of 8.75 g / L was obtained. 3 The first catalyst.

[0061] The preparation of the second mixed slurry is the same as in Comparative Example 3. The second mixed slurry was coated onto the first catalyst at a concentration of 94.18 g / L, and after drying and calcination, the final Pd-Rh type catalyst was obtained, in which the Pd content was 32.75 g / L. 3 The Rh content is 3g / ft 3 It was named Comparative Catalyst 7#.

[0062] Example 1: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain a mixed solution. Using the equal volume impregnation method, impregnate this mixed solution onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain the upper catalyst powder B1.

[0063] 0.25g of rhodium nitrate solution and 2.5g of tetramethylammonium hydroxide were added to 50g of water and stirred evenly to obtain a mixed solution. Then, the mixed solution was impregnated onto 96.53g of second cerium zirconium rare earth oxygen storage material (with CeO2 content of 23%) using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C14.

[0064] 3.06 g of aluminum nitrate, 0.16 g of phosphoric acid solution, 0.1 mol / L of urea solution, and pure water were mixed evenly, with the concentration of the aluminum phosphate precursor controlled at 0.01 mol / L and the molar ratio of (P+Al) to urea controlled at 1:12 to obtain a mixed solution. 96.78 g of powdered C14 was added to pure water, with the solid content controlled at 30%. After stirring evenly, the mixture was placed in an 80°C water bath and the mixed solution was added dropwise. The mixture was stirred for 6 hours, filtered and washed, dried at 100°C for 6 hours, and calcined in air at 500°C for 4 hours at a heating rate of 2°C / min to obtain Rh second cerium-zirconium composite oxide C25 uniformly coated with P2O5-Al2O3.

[0065] S4. 45g of Rh second cerium-zirconium composite oxide C25, 45g of catalyst powder B1, 5g of alumina sol, 5g of barium carbonate, and 200g of pure water were mixed and ball-milled to obtain a second mixed slurry. The second mixed slurry was coated onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, the final Pd-Rh type catalyst was obtained, wherein the Pd content was 32.75g / ft. 3 The Rh content is 3g / ft 3 It is named Catalyst 1. Specific implementation details are as follows: Figure 4 As shown. Example 2: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain a mixed solution. Using the equal volume impregnation method, impregnate the mixed solution onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain the upper catalyst powder B1.

[0066] 0.25g of rhodium nitrate solution and 2.5g of tetramethylammonium hydroxide were added to 50g of water and stirred evenly to obtain a mixed solution. Then, the mixed solution was impregnated onto 96.53g of second cerium zirconium rare earth oxygen storage material (with CeO2 content of 23%) using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C14.

[0067] 3.06 g of aluminum nitrate, 0.16 g of phosphoric acid solution, 0.1 mol / L of urea solution, and pure water were mixed evenly, with the concentration of the aluminum phosphate precursor controlled at 0.01 mol / L and the molar ratio of (P+Al) to urea controlled at 1:10 to obtain a mixed solution. 96.78 g of upper catalyst powder C14 was added to pure water, with the solid content controlled at 30%. After stirring evenly, the mixture was placed in an 80°C water bath and the mixed solution was added dropwise. After stirring for 6 h, the mixture was filtered and washed, dried at 100°C for 6 h, and calcined in air at 500°C for 4 h with a heating rate of 2°C / min to obtain Rh second cerium-zirconium composite oxide C26 uniformly coated with P2O5-Al2O3.

[0068] S4. 45g of Rh second cerium-zirconium composite oxide C26, 45g of catalyst powder B1, 5g of alumina sol, 5g of barium carbonate, and 200g of pure water were mixed and ball-milled to obtain a second mixed slurry. The second mixed slurry was coated onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, the final Pd-Rh type catalyst was obtained, wherein the Pd content was 32.75g / ft. 3 The Rh content is 3g / ft 3 It was named Catalyst 2.

[0069] Example 3: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain a mixed solution. Using the equal volume impregnation method, impregnate this mixed solution onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain the upper catalyst powder B1.

[0070] 0.25g of rhodium nitrate solution and 2.5g of tetramethylammonium hydroxide were added to 50g of water and stirred evenly to obtain a mixed solution. Then, the mixed solution was impregnated onto 96.53g of second cerium zirconium rare earth oxygen storage material (with CeO2 content of 23%) using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C14.

[0071] 3.06 g of aluminum nitrate, 0.16 g of phosphoric acid solution, 0.1 mol / L of urea solution, and pure water were mixed evenly, with the concentration of the aluminum phosphate precursor controlled at 0.01 mol / L and the molar ratio of (P+Al) to urea controlled at 1:6 to obtain a mixed solution. 96.78 g of upper catalyst powder C14 was added to pure water, with the solid content controlled at 30%. After stirring evenly, the mixture was placed in an 80°C water bath and the mixed solution was added dropwise. After stirring for 6 h, the mixture was filtered and washed, dried at 100°C for 6 h, and calcined in air at 500°C for 4 h with a heating rate of 2°C / min to obtain Rh second cerium-zirconium composite oxide C27 uniformly coated with P2O5-Al2O3.

[0072] S4. 45g of Rh second cerium-zirconium composite oxide C27, 45g of catalyst powder B1, 5g of alumina sol, 5g of barium carbonate, and 200g of pure water were mixed and ball-milled to obtain a second mixed slurry. The second mixed slurry was coated onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, the final Pd-Rh type catalyst was obtained, wherein the Pd content was 32.75g / ft. 3 The Rh content is 3g / ft 3 It was named Catalyst 3.

[0073] Example 4: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain a mixed solution. Using the equal volume impregnation method, impregnate this mixed solution onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain the upper catalyst powder B1.

[0074] 0.25g of rhodium nitrate solution and 2.5g of tetramethylammonium hydroxide were added to 50g of water and stirred evenly to obtain a mixed solution. Then, the mixed solution was impregnated onto 97.79g of second cerium zirconium rare earth oxygen storage material (with CeO2 content of 23%) using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C15.

[0075] 1.862 g of aluminum nitrate, 0.098 g of phosphoric acid solution, 0.1 mol / L urea solution, and pure water were mixed evenly, with the concentration of the aluminum phosphate precursor controlled at 0.01 mol / L and the molar ratio of (P+Al) to urea controlled at 1:10 to obtain a mixed solution. 98.04 g of upper catalyst powder C15 was added to pure water, with the solid content controlled at 30%. After stirring evenly, the mixture was placed in an 80°C water bath and the mixed solution was added dropwise. After stirring for 6 h, the mixture was filtered and washed, dried at 100°C for 6 h, and calcined in air at 500°C for 4 h with a heating rate of 2°C / min to obtain Rh second cerium-zirconium composite oxide C28 uniformly coated with P2O5-Al2O3.

[0076] S4. 45g of Rh second cerium-zirconium composite oxide C28, 45g of catalyst powder B1, 5g of alumina sol, 5g of barium carbonate, and 200g of pure water were mixed and ball-milled to obtain a second mixed slurry. The second mixed slurry was coated onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, the final Pd-Rh type catalyst was obtained, wherein the Pd content was 32.75g / ft. 3 The Rh content is 3g / ft 3 It was named Catalyst 4.

[0077] Example 5: The first catalyst was prepared in the same manner as in Comparative Example 1. S3. Add 100g of water to 2g of palladium nitrate solution and stir evenly to obtain a mixed solution. Using the equal volume impregnation method, impregnate this mixed solution onto 98g of La2O3-Al2O3 (where the La2O3 content is 15%). After standing for 1h, pre-dry at 100℃ for 4h and calcine at 500℃ for 2h to obtain the upper catalyst powder B1.

[0078] 0.25g of rhodium nitrate solution and 2.5g of tetramethylammonium hydroxide were added to 50g of water and stirred evenly to obtain a mixed solution. Then, the mixed solution was impregnated onto 90.68g of second cerium zirconium rare earth oxygen storage material (with CeO2 content of 23%) using the equal volume impregnation method. After standing for 1 hour, it was pre-dried at 100℃ for 4 hours and then calcined at 500℃ for 2 hours to obtain the upper catalyst powder C16.

[0079] 8.62 g of aluminum nitrate, 0.45 g of phosphoric acid solution, 0.1 mol / L of urea solution, and pure water were mixed evenly. The concentration of the aluminum phosphate precursor was controlled at 0.01 mol / L, and the molar ratio of (P+Al) to urea was controlled at 1:10 to obtain a mixed solution. 90.93 g of powdered C16 was added to pure water, with the solid content controlled at 30%. After stirring evenly, the mixture was placed in an 80°C water bath and the mixed solution was added dropwise. The mixture was stirred for 6 hours, filtered and washed, dried at 100°C for 6 hours, and calcined in air at 500°C for 4 hours at a heating rate of 2°C / min to obtain Rh second cerium-zirconium composite oxide C29 uniformly coated with P2O5-Al2O3.

[0080] S4. 45g of Rh second cerium-zirconium composite oxide C29, 45g of catalyst powder B1, 5g of alumina sol, 5g of barium carbonate, and 200g of pure water were mixed and ball-milled to obtain a second mixed slurry. The second mixed slurry was coated onto the first catalyst at a concentration of 94.18g / L, and after drying and calcination, the final Pd-Rh type catalyst was obtained, wherein the Pd content was 32.75g / ft. 3 The Rh content is 3g / ft 3 It was named Catalyst 5.

[0081] Example 6: The preparation of the first mixed slurry was the same as in Comparative Example 1. The first mixed slurry was coated at a concentration of 137.34 g / L onto a honeycomb ceramic substrate with a diameter of 118.4 mm, a length of 127 mm, and a mesh size of 750. After drying and calcination, a Pd content of 8.75 g / L was obtained. 3 The first catalyst.

[0082] The preparation of the second mixed slurry is the same as in Example 2. The second mixed slurry was coated onto the first catalyst at a concentration of 94.18 g / L, and after drying and calcination, the final Pd-Rh type catalyst was obtained, in which the Pd content was 32.75 g / L. 3 The Rh content is 3g / ft 3 It was named Catalyst 6.

[0083] The automotive exhaust gas treatment catalysts of Examples 1-5 and Comparative Examples 1-6 prepared above were aged under air conditions at 1050°C for 20 hours.

[0084] Sample activity testing conditions: Atmosphere: CO 4500 ppm, NO 1250 ppm, CO2 11.0%, H2O 10.0%, O2 3800 ppm, C3H6 220 ppm, C3H8 110 ppm, H2 1500 ppm, N2 as balance gas, λ=1, space velocity 40000 h⁻¹ -1After activation at 600℃ in a full atmosphere for 2 hours, the temperature was lowered to below 150℃ for transient temperature rise testing at a rate of 5℃ / min. The table below shows T... 50 The temperature at which the conversion rate reaches 50%, also known as the ignition temperature, T. 90 It is the temperature at which the conversion rate reaches 90%, also known as the complete conversion temperature.

[0085] Oxygen storage capacity test conditions: Referring to Minwei Zhao's literature, the dynamic oxygen storage capacity (DOSC) is calculated by measuring the amount of carbon dioxide absorbed or released at a specific reaction temperature. In this study, the DOSC value was calculated based on the amount of carbon dioxide produced at 500℃.

[0086] Literature: Minwei Zhao, Meiqing Shen, et al. Ce–Zr–Sr ternary mixed oxidesstructural characteristics and oxygen storage capacity [J]. Journal of Alloysand Compounds 457 (2008) 578–586.

[0087] Table 1. Aging performance (T) of catalysts in Examples 1-5 and Comparative Examples 1-6. 50 T 90 Comparison of oxygen storage capacity From Table 1 and Figure 1 , 2 Results 3 show that, under the same precious metal conditions, after aging at 1050℃ for 20h, all catalysts exhibited significantly higher T values ​​for CO, NOx, C3H6, and C3H8 compared to the comparative catalyst. 50 and T 90 The levels of these catalysts are all higher than those in the examples, and the oxygen storage capacity is significantly lower than that in the examples of this invention. This indicates that the catalyst of this invention, after improvement of the Rh-supported material preparation process, not only enhances catalytic activity but also greatly maintains the oxygen storage capacity of the support, especially with a greater improvement in NOx performance.

[0088] As shown in Table 1, in Embodiment 1 of the present invention, NOx at T 50Compared to Comparative Example 3, the temperature was reduced by 33°C. Comparative Example 3 also used P and Al for modification, but its process was a conventional impregnation method. The local concentration of the solution was too high, resulting in rapid adsorption and failure to nucleate and form a uniform and complete coating layer on the surface of each particle. Its P and Al may be distributed in an isolated, plate-like form on the surface of the support or in the pores. In contrast, during the phosphorus-aluminum coating of the catalyst of Example 1 of this invention, urea slowly decomposes, causing the pH of the entire solution system to rise uniformly. The precipitation reaction is homogeneous in the solution and proceeds synchronously and uniformly on the surface of all particles. Therefore, the catalyst of Comparative Example 3 cannot effectively inhibit the sintering and migration of Rh, resulting in its performance after aging being far inferior to that of this invention. This also proves that the urea slow-release homogeneous precipitation method has a significant advantage over the traditional impregnation method in stabilizing Rh activity. Comparative Examples 2 and 3 are compared with Example 1 of this invention. Comparative Example 2 only uses organic base to regulate the NOx T of phosphorus-aluminum modification, and Comparative Example 3 only uses the ordinary impregnation method. 50 The temperatures were 38°C and 33°C higher, respectively, both significantly lower than those in Example 1 of this invention, which simultaneously employed organic base regulation and urea slow-release precipitation coating. This fully demonstrates the inseparable synergistic effect between the two technical features of "organic base regulation" and "urea slow-release homogeneous precipitation coating," producing a technical effect far exceeding the simple superposition of their individual uses. As shown in Table 1, when the molar ratio of (P+Al) to urea is in the range of 1:12 to 1:6, the catalyst exhibits excellent and significantly superior overall performance compared to the comparative example. In particular, when the molar ratio is 1:10, the T values ​​of CO, NOx, C3H6, and C3H8 are significantly higher. 50 and T 90 The results showed the lowest values, achieving the best technical effect. This indicates that the preferred molar ratio of phosphorus aluminum precursor to urea is 1:10, which achieves a good balance between precipitation rate and coating integrity. Therefore, this ratio is the preferred solution of this invention. The oxygen storage capacity of Comparative Examples 4 and 6 is much lower than that of all embodiments of this invention, proving that this invention has successfully solved the fatal defect that "phosphorus aluminum modified carriers cannot provide oxygen storage performance". The oxygen storage capacity of Comparative Example 1 after aging is 385 μmol O2 / g, while the embodiments of this invention effectively protect the cerium-zirconium carrier through the P2O5-Al2O3 coating layer, and its oxygen storage capacity is increased by about 33%-41%. This proves that the coating structure of this invention can effectively inhibit the sintering deterioration of the cerium-zirconium carrier at high temperatures, thereby maintaining its crucial oxygen storage capacity. Examples 4 and 5 represent different mass ratios of P2O5-Al2O3 to cerium-zirconium materials, and their oxygen storage capacity still remains at a high level. This indicates that the coating layer formed by the "urea slow-release homogeneous precipitation method" of this invention is porous and does not block the pores of the cerium-zirconium material, ensuring the transport and storage of oxygen.

[0089] To verify the uniformity and integrity of the P2O5-Al2O3 coating layer prepared in this invention, we used SO2 selective poisoning experiments to indirectly characterize the protective effect of the coating layer on Rh active sites, and nitrogen adsorption-desorption (BET) specific surface area and pore size distribution to directly characterize the formation of a uniform, porous, and thermally stable P2O5-Al2O3 coating layer on the surface of the Rh second cerium-zirconium composite oxide. The experimental results are recorded in Tables 2 and 3.

[0090] Table 2. Catalyst specific surface area test results The results showed that after harsh aging, the specific surface area of ​​the uncoated Comparative Example 2 decreased sharply to 25 m² / g, indicating that the cerium-zirconium support itself underwent severe sintering and pore collapse. In contrast, the specific surface area of ​​Example 2 of this invention remained at 58 m² / g, far higher than Comparative Example 2, and even significantly higher than Comparative Example 3. This strongly demonstrates that the uniform P₂O₅-Al₂O₃ coating effectively inhibited the sintering of the cerium-zirconium support at high temperatures, enabling it to maintain a high specific surface area, which is the structural basis for its high oxygen storage performance. Although the specific surface area of ​​Comparative Example 3 was higher than that of Comparative Example 2, it was far lower than that of this invention, indicating that its coating was uneven and incomplete, failing to provide the same level of protection. The most probable pore size of Example 2 of this invention remained at 12.0 nm, maintaining a suitable most probable pore size and the largest pore volume. This proves that the coating layer formed by the "urea slow-release homogeneous precipitation method" is not only complete but also maintains structural stability at high temperatures, preventing pore merging and collapse, and maintaining excellent mass transfer channels.

[0091] The catalysts of Example 2, Comparative Example 2 and Comparative Example 3 were selected for aging performance comparison test at 1050℃ / 20h.

[0092] The SO2 poisoning experiment was conducted in a micro fixed-bed reactor. The specific steps are as follows: Initial performance testing: The catalyst sample was placed in the reactor, and sulfur-free simulated tail gas was introduced. The gas composition was: NO: 1250ppm, CO: 4500ppm, C3H8: 110ppm, C3H6: 220ppm, H2O: 10%, CO2: 11%, O2: 5600ppm, N2: balance gas, space velocity 40000h. -1 The heating rate was 10℃ / min. Under these conditions, the ignition performance of the catalyst was tested, and the initial NOx T of each sample was recorded. 50SO2 poisoning treatment: The reaction system temperature was stabilized at 300℃. While maintaining the basic composition of the simulated tail gas, SO2 at a concentration of 15 ppm was continuously introduced into the reaction gas for 30 minutes. After poisoning, activity testing was performed. SO2 introduction was stopped, and the simulated tail gas was switched back to sulfur-free form. The mixture was then purged at 300℃ for 15 minutes. Subsequently, the temperature was lowered to 160℃, and a programmed temperature rise experiment was conducted again. Under these conditions, the ignition performance of the catalyst was tested, and the NOx T value after poisoning of each sample was recorded. 50 value.

[0093] Table 3 Results of the SO2 selective poisoning experiment The results show that the NOx conversion activity of the catalyst in Example 2 of this invention only decreased slightly after SO2 poisoning, and the performance degradation was much smaller than that in Comparative Examples 2 and 3. This result strongly demonstrates that the unique preparation process of this invention successfully constructs a continuous, dense, and defect-free aluminum phosphorus protective layer on the surface of the Rh / cerium-zirconium composite oxide. This coating layer can effectively prevent SO2 gaseous poisons from contacting and poisoning the internal Rh active sites.

[0094] This superior "anti-toxicity" capability, along with the aforementioned "anti-high-temperature aging" capability, mutually reinforces each other, demonstrating the dual advantages of this uniform coating layer in terms of physical isolation and chemical anchoring. While Comparative Example 3 also underwent phosphorus-aluminum modification, its uneven coating and defects prevented it from providing the same level of protection, further highlighting the technical advantages of the method described in this invention.

[0095] Furthermore, the automotive exhaust gas treatment catalysts prepared in Comparative Example 7 and Example 6 were aged at 1050℃ for 20 hours in air. Then, rich and lean cycles were performed at an engine exhaust flow rate of 40 kg / h, an engine speed of 1800 rpm, and a λ = 0.95-1.05. The bench oxygen storage at 500℃ was obtained by integrating the voltage signal changes collected by the front and rear oxygen sensors. Ignition performance was tested according to the standard HJ-T331-2006, "Technical Requirements for Gasoline Catalytic Converters for Environmental Protection Products". The comparison results of ignition temperature and oxygen storage are as follows: Figure 5 , Figure 6 .

[0096] from Figure 5 and 6As can be seen, after aging at 1050℃ for 20h, the ignition temperatures of CO, THC, and NOx in Example 6 were reduced by 25℃, 24℃, and 25℃ respectively compared to Comparative Example 7 after bench testing, and the oxygen storage capacity was increased by 15% compared to Comparative Example 7. After the Rh-supported second cerium-zirconium oxygen storage material catalyst was uniformly coated with P2O5-Al2O3, the degradation of the second cerium-zirconium oxygen storage material could be further reduced, thus improving its aging performance. This indicates that the catalyst of the present invention has excellent high thermal stability and durability.

[0097] Furthermore, the automotive exhaust treatment catalysts prepared in Comparative Example 7 and Example 6 were aged at 1050°C for 20 hours in air, and then subjected to a full vehicle test on a 1.5L engine. The test was conducted according to the WLTC cycle test of Method I of GB18352.6-2016 "Limits and Measurement Methods for Pollutant Emissions from Light-Duty Vehicles (China VI)". The performance comparison results are as follows. Figures 7-10 .

[0098] from Figures 7-10 As can be seen, after aging at 1050℃ for 20h, the catalyst in Example 6 showed slightly better CO and THC performance than the catalyst in Comparative Example 7 after aging, while NOx emissions showed a performance improvement of more than 60%, mainly in the ultra-high speed stage. This indicates that when applied to this vehicle model, Rh loaded on cerium-zirconium composite oxide and uniformly coated with phosphorus-aluminum can significantly improve the anti-aging performance of NOx, exhibiting excellent high thermal stability and durability.

[0099] The regulatory mechanism of Rh surface distribution by organic bases: When impregnating the precursor solution of Rh salt, the mechanism of adding organic bases (such as tetramethylammonium hydroxide) is that the cations in the organic base molecules (such as quaternary ammonium ions) can preferentially adsorb onto the surface of the second cerium-zirconium composite oxide support through electrostatic interactions. This adsorption changes the charge distribution and chemical environment of the support surface. On the one hand, it competes with Rh complex ions (such as [Rh(OH)2]⁺) for adsorption, delaying their rapid adsorption; on the other hand, it regulates the diffusion and anchoring process of Rh salt precursors within the pores of the support, allowing Rh species to be more densely and preferentially distributed on the surface and near-surface regions of the support particles after calcination, rather than in the deeper layers or randomly distributed. This "surface enrichment" effect predetermines ideal locations for subsequent coating treatments, ensuring that the protective layer can directly act on most of the Rh active sites.

[0100] Construction of a Uniform Porous Coating Layer by Urea Slow-Release Homogeneous Precipitation Method: Traditional equal-volume impregnation methods (as shown in Comparative Example 3) for phosphorus-aluminum modification involve directly and rapidly impregnating high-concentration aluminum salt and phosphate solutions onto Rh-loaded cerium-zirconium materials. This method inherently suffers from uneven coating, pore blockage, and weak anchoring. This invention overcomes these defects by employing a "urea slow-release homogeneous precipitation method." The mechanism involves the slow and uniform decomposition of urea in an 80-100℃ water bath, generating OH-. - and CO3 2- The presence of ions causes the pH of the entire solution system to rise gradually and synchronously. When the pH value for precipitation is reached, aluminum and phosphate ions can homogeneously nucleate in the solution and undergo a simultaneous and uniform precipitation reaction on the surface of all Rh / cerium-zirconium particles. This "growth" process from the interior of the solution to the particle surface forms a complete, dense, and controllable-thickness inorganic shell. Simultaneously, during precipitation and subsequent calcination, the gases produced by urea decomposition and the escape of water of crystallization create abundant mesoporous structures in the coating layer, ensuring its porous nature. This provides unobstructed mass transfer channels for reactant gas molecules while effectively preventing the migration and sintering of Rh particles at high temperatures.

[0101] Synergistic stabilizing effect of the P2O5-Al2O3 coating layer: The final P2O5-Al2O3 coating layer achieves stabilization through both physical and chemical processes. Physical isolation effect: This coating layer acts as a physical barrier, isolating the Rh particles and cerium-zirconium support from the high-temperature aging environment (especially the hydrothermal atmosphere). This barrier effectively inhibits the surface migration and Ostwald ripening of Rh particles at high temperatures, preventing them from agglomerating into large particles; at the same time, it also protects the cerium-zirconium support, slowing down its specific surface area loss and crystal phase transformation, thereby maintaining the support's crucial oxygen storage capacity.

[0102] Chemical bonding (Rh-OP bond formation): During calcination, P species can strongly interact with Rh species on the surface, forming Rh-OP chemical bonds. This bonding acts like "chemical anchoring," firmly fixing Rh atoms to the support surface and fundamentally inhibiting Rh... 3+ Migration to the alumina lattice (if present) avoids the formation of inactive rhodium aluminate. Meanwhile, the highly thermally stable AlPO4 formed by the reaction of P2O5 and Al2O3 at the interface further strengthens the structural integrity of the coating layer, ensuring its stability even under harsh aging conditions at 1050℃.

[0103] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A catalyst for treating automotive exhaust gases, comprising a substrate and an active coating applied to the surface of the substrate, characterized in that, The active coating comprises an upper Pd-Rh coating and a lower Pd coating. The upper Pd-Rh coating is made of Rh second cerium-zirconium composite oxide uniformly coated with phosphorus aluminum P2O5-Al2O3, lanthanum alumina loaded with Pd, additives, and a binder. The mass ratio of P2O5-Al2O3 to the second cerium-zirconium rare earth oxygen storage material is 1:50 to 1:

10. The phosphorus aluminum P2O5-Al2O3 uniformly coated Rh second cerium-zirconium rare earth oxygen storage material is obtained by enriching Rh elements on the surface of the second cerium-zirconium composite oxide particles and uniformly coating them with a porous P2O5-Al2O3 composite.

2. The automotive exhaust gas treatment catalyst according to claim 1, characterized in that, The preparation method of Rh second cerium zirconium rare earth oxygen storage material uniformly coated with phosphorus aluminum P2O5-Al2O3 is as follows: the phosphorus aluminum precursor is uniformly coated on the surface of the second cerium zirconium composite oxide particles enriched with Rh element by urea slow-release homogeneous precipitation. The Rh element enrichment on the surface of the second cerium zirconium composite oxide particles is specifically obtained by impregnating the second cerium zirconium composite oxide particles with an Rh salt solution containing organic alkali.

3. The automotive exhaust gas treatment catalyst according to claim 2, characterized in that, The organic base is one or more of ethylenediamine, 1,3-propanediamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylethylammonium hydroxide, or dimethyldiethylammonium hydroxide.

4. The automotive exhaust gas treatment catalyst according to claim 1, characterized in that, The lower Pd coating is made of Pd-loaded lanthanum alumina La2O3-Al2O3, Pd-loaded first cerium zirconium rare earth oxygen storage material, additives, and binders. The additives are alkaline earth metal salts.

5. The automotive exhaust gas treatment catalyst according to claim 4, characterized in that, Lanthanum alumina La2O3-Al2O3 is lanthanum-modified gamma alumina γ-Al2O3 with a La2O3 content of 0~25%, and the La2O3 content is not 0.

6. The automotive exhaust gas treatment catalyst according to claim 1, characterized in that, Both the first and second cerium-zirconium rare earth oxygen storage materials are cerium-zirconium solid solutions.

7. The automotive exhaust gas treatment catalyst according to claim 5, characterized in that, Both the first and second cerium-zirconium rare earth oxygen storage materials are one or more of lanthanum, praseodymium, neodymium, or yttrium-modified cerium-zirconium solid solutions.

8. The automotive exhaust gas treatment catalyst according to claim 1, characterized in that, The first cerium-zirconium rare earth oxygen storage material contains 30–85 wt% cerium dioxide (CeO2), while the second cerium-zirconium rare earth oxygen storage material contains 10–50 wt% CeO2.

9. The automotive exhaust gas treatment catalyst according to claim 1, characterized in that, The mass ratio of the Pd-loaded La2O3-Al2O3 material to the first cerium-zirconium rare earth oxygen storage material is 1:10 to 10:1, and the mass ratio of the P2O5-Al2O3-coated Rh second cerium-zirconium rare earth oxygen storage material to the Pd-loaded lanthanum alumina is 5:1 to 1:

5.

10. A method for preparing an automotive exhaust gas treatment catalyst as described in any one of claims 1-9, characterized in that, The process involves sequentially coating an upper Pd-Rh coating and a lower Pd coating onto a substrate from bottom to top. The preparation of the upper Pd-Rh coating specifically includes: 1) impregnating the second cerium-zirconium rare earth oxygen storage material with an Rh salt solution to obtain a Rh second cerium-zirconium rare earth oxygen storage material with Rh enriched on the surface of the second cerium-zirconium rare earth oxygen storage material; 2) uniformly precipitating and coating phosphorus and aluminum onto the Rh second cerium-zirconium rare earth oxygen storage material using an aluminum salt solution, phosphate solution, and urea solution via a "urea slow-release homogeneous precipitation method"; 3) forming a coating by uniformly coating the Rh second cerium-zirconium composite oxide with phosphorus and aluminum P2O5-Al2O3, Pd-loaded lanthanum alumina, additives, and binders.

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