A three-way catalyst to enhance automobile exhaust purification

Abstract

This invention provides a three-way catalytic converter for enhanced automotive exhaust purification. The invention also provides a method for preparing the three-way catalytic converter. The three-way catalytic converter prepared according to the method has three coatings: upper, middle, and lower. The middle coating is a Cu-Ni-La solid solution, which acts as a physical barrier to isolate the palladium in the lower coating and the rhodium in the upper coating. The three-way catalytic converter of this invention has enhanced CO, NOx, and HC conversion capabilities, making it suitable for use in automotive exhaust purification.

Description

Technical Field

[0001] This invention relates to the field of catalysts, and more specifically, to a three-way catalyst for enhancing the purification of automobile exhaust. Background Technology

[0002] In today's society, with the development of the economy and transportation, the number of cars has increased dramatically, and vehicle exhaust pollution has become an increasingly serious problem. Three-way catalysts (TWCs) are widely recognized as the most effective means of controlling gasoline vehicle exhaust pollution, simultaneously reducing emissions of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). The most commonly used active components in three-way catalysts are precious metals such as palladium, platinum, and rhodium. Palladium is abundant and cheaper, making it one of the research hotspots in the development of three-way catalysts; while rhodium has an irreplaceable reducing ability for the efficient conversion of NOx, and its oxidation activity for CO and HC is no less than that of platinum and palladium, so it is also widely used.

[0003] To suppress the Oswald ripening of palladium and rhodium under high-temperature conditions, which leads to alloy formation and reduced catalyst activity, current ternary catalysts generally employ a two-layer structure: a lower coating loaded with palladium and an upper coating loaded with rhodium. Coating materials typically include cerium-zirconium solid solutions, alumina, zirconium oxide, and other additives. However, under high-temperature, oxygen-rich conditions, the rhodium in the upper coating of the double-layer structure easily migrates to the lower coating and interacts with the palladium, thus reducing catalyst activity. Meanwhile, cerium-zirconium solid solutions, as coating additives, can significantly improve the catalyst's resistance to sintering and its oxygen storage / release properties, making them key materials in ternary catalysts. However, existing cerium-zirconium solid solutions are mainly prepared by solid-state methods, co-precipitation methods, and hydrothermal methods, which have limitations in performance.

[0004] Therefore, more three-way catalysts with good performance still need to be developed. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a method for preparing a three-way catalyst and the three-way catalyst obtained therefrom, which has good catalytic efficiency and thus enhances the purification capability of automobile exhaust.

[0006] The preparation method of the present invention includes:

[0007] Step 1: Preparation of the lower cerium-zirconium solid solution

[0008] A metal salt solution is obtained by mixing cerium salt solution, zirconium salt solution and rare earth element salt solution, and a surfactant polyhydroxy fatty acid amide is added. A ball milling bead is added to an alkaline solution, and the metal salt solution is added dropwise while ball milling. After the addition is complete, stirring is continued. Then the ball milling bead is filtered out, and a dispersant is added. The precipitate is filtered out, washed, dried, calcined and sieved to obtain the lower layer of cerium-zirconium solid solution.

[0009] Step 2: Preparation of the upper cerium-zirconium solid solution

[0010] A metal salt solution is obtained by mixing cerium salt solution, zirconium salt solution and rare earth element salt solution, and a surfactant polyhydroxy fatty acid amide is added. A ball milling bead is added to an alkaline solution, and the metal salt solution is added dropwise while ball milling. After the addition is complete, stirring is continued. Then the ball milling bead is filtered out, and a dispersant is added. The precipitate is filtered out, washed, dried, calcined and sieved to obtain the lower layer of cerium-zirconium solid solution.

[0011] Step 3: Applying the lower coating layer

[0012] After ball milling La2O3-ZrO3 to a particle size of 5-15 μm, it is added to pure water along with the lower cerium-zirconium solid solution and stirred evenly. Then, palladium salt solution is added dropwise and mixed evenly. The mixture is then coated onto a honeycomb support, dried, and calcined to obtain a catalyst semi-finished product coated with the lower coating.

[0013] Step 4: Applying the intermediate coating:

[0014] A copper salt solution, a nickel salt solution, and a lanthanum salt solution are mixed to obtain a metal salt solution. A ball milling bead is added to an alkaline solution, and the metal salt solution is added dropwise while ball milling. After the addition is complete, stirring is continued. The ball milling bead is then filtered out, and a dispersant is added. The mixture is coated onto the catalyst semi-finished product with a lower coating prepared in step 3. The lower coating is then covered, dried, and calcined to obtain a catalyst semi-finished product with a middle and lower coating.

[0015] Step 5: Applying the upper coating

[0016] After ball milling La2O3-ZrO3 to a particle size of 5-15 μm, it is added to pure water along with the upper cerium-zirconium solid solution and stirred evenly. Then, a rhodium salt solution is added dropwise and mixed evenly. The mixture is then coated onto the catalyst semi-finished product coated with the middle and lower coatings, covered with the middle coating, dried, and calcined to obtain the three-way catalyst finished product.

[0017] In one implementation, in step 1:

[0018] The anions of the cerium salt, zirconium salt, and rare earth element salt are selected from at least one of nitrate ions, halide ions, sulfate ions, and acetate ions, preferably nitrate ions. The rare earth elements are selected from at least one of La, Y, Pr, and Nd, preferably Y and La. The amounts of cerium salt, zirconium salt, and rare earth element salt, based on their oxides, can be 20–60:30–70:5–25. In a preferred embodiment, the rare earth elements are selected from Y and La, and the amounts of cerium salt, zirconium salt, and rare earth element salt, based on their oxides, are CeO2:ZrO2:Y2O3:La2O3 = 30–40:45–55:10–15:5–10, preferably 40:45:10:5 and 30:55:10:5.

[0019] The structure of the polyhydroxy fatty acid amide is as follows:

[0020]

[0021] Wherein, R1 is selected from alkyl groups of C9 to C21, preferably alkyl groups of C11 to C17;

[0022] R2 is selected from C1-6 alkyl groups, preferably C1-4 alkyl groups;

[0023] n is selected from 2, 3, 4, 5, or 6.

[0024] Preferably, the polyhydroxy fatty acid amide is selected from at least one of lauroyl N-n-propyl glucamide, tridecanoyl N-n-propyl glucamide, and stearoyl N-n-propyl glucamide.

[0025] The amount of polyhydroxy fatty acid amide used is 5-30% of the total amount of cerium, zirconium, and rare earth element oxides, preferably 10-15%.

[0026] The alkaline solution is an aqueous solution of ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, preferably ammonia solution, and more preferably 15-25% ammonia solution. The amount of alkaline substances such as ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate used is 2 to 12 times the molar amount of metal ions in the metal salt solution, preferably 5 to 10 times.

[0027] The grinding beads may include large beads with a diameter of 14-30 mm and small beads with a diameter of 6-13 mm, wherein the diameter ratio of the large beads to the small beads is greater than 1.4 and the volume ratio is greater than 2. Preferably, the large beads have a diameter of 16-20 mm, the small beads have a diameter of 8-12 mm, and the diameter ratio of the large beads to the small beads is between 1.5 and 2.0, and the volume ratio is between 2.5 and 4.0.

[0028] The dispersant is selected from at least one of dodecyltrimethylammonium bromide, dodecyldimethylbenzylammonium bromide, dodecyltrimethylammonium chloride, dodecyldimethylbenzylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyldimethylbenzylammonium bromide, hexadecyltrimethylammonium chloride, and hexadecyldimethylbenzylammonium chloride. The amount of dispersant used is 1-20% of the total amount of cerium, zirconium, and rare earth element oxides, preferably 5-10%.

[0029] The roasting temperature in step 1 is 620–720°C, preferably 650–700°C.

[0030] In one implementation, in step 2:

[0031] The anions of the cerium salt, zirconium salt, and rare earth element salt are selected from at least one of nitrate ions, halide ions, sulfate ions, and acetate ions, preferably nitrate ions. The rare earth elements are selected from at least one of La, Y, Pr, and Nd, preferably Y and La. The amounts of cerium salt, zirconium salt, and rare earth element salt, based on their oxides, can be 20–60:30–70:5–25. In a preferred embodiment, the rare earth elements are selected from Y and La, and the amounts of cerium salt, zirconium salt, and rare earth element salt, based on their oxides, are CeO2:ZrO2:Y2O3:La2O3 = 30–40:35–50:5–10:10–15, preferably 40:45:5:10 and 35:50:5:10.

[0032] The structure of the polyhydroxy fatty acid amide is as follows:

[0033]

[0034] Wherein, R1 is selected from alkyl groups of C9 to C21, preferably alkyl groups of C11 to C17;

[0035] R2 is selected from C1-6 alkyl groups, preferably C1-4 alkyl groups;

[0036] n is selected from 2, 3, 4, 5, or 6.

[0037] Preferably, the polyhydroxy fatty acid amide is selected from at least one of lauroyl N-n-propyl glucamide, tridecanoyl N-n-propyl glucamide, and stearoyl N-n-propyl glucamide.

[0038] The amount of polyhydroxy fatty acid amide used is 5-30% of the total amount of cerium, zirconium, and rare earth element oxides, preferably 10-15%.

[0039] The alkaline solution is an aqueous solution of ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, preferably ammonia solution, and more preferably 15-25% ammonia solution. The amount of alkaline substances such as ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate used is 2 to 12 times the molar amount of metal ions in the metal salt solution, preferably 5 to 10 times.

[0040] The grinding beads may include large beads with a diameter of 14-30 mm and small beads with a diameter of 6-13 mm, wherein the diameter ratio of the large beads to the small beads is greater than 1.4 and the volume ratio is greater than 2. Preferably, the large beads have a diameter of 16-20 mm, the small beads have a diameter of 8-12 mm, and the diameter ratio of the large beads to the small beads is between 1.5 and 2.0, and the volume ratio is between 2.5 and 4.0.

[0041] The dispersant is selected from at least one of dodecyltrimethylammonium bromide, dodecyldimethylbenzylammonium bromide, dodecyltrimethylammonium chloride, dodecyldimethylbenzylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyldimethylbenzylammonium bromide, hexadecyltrimethylammonium chloride, and hexadecyldimethylbenzylammonium chloride. The amount of dispersant used is 1-20% of the total amount of cerium, zirconium, and rare earth element oxides, preferably 5-10%.

[0042] The roasting temperature in step 2 is 620–720°C, preferably 650–700°C.

[0043] In one implementation, in step 3:

[0044] The La2O3-ZrO2 contains 1-5 wt% La2O3, preferably 3-4 wt%. The mass ratio of La2O3-ZrO2 to the lower cerium-zirconium solid solution is 0.8-1.5:1, preferably 0.9-1.1:1.

[0045] The amount of palladium salt solution, calculated as palladium oxide, is 0.5 to 3% of the total amount of La2O3-ZrO2 and cerium-zirconium solid solution, preferably 1 to 2%.

[0046] The coating amount in step 3 is 50-240 g / L, preferably 100-160 g / L.

[0047] The roasting temperature in step 3 is 530–570°C, preferably 540–560°C.

[0048] In one implementation, step 4:

[0049] The anions of copper, nickel, and lanthanum salts are selected from at least one of nitrate ions, halide ions, sulfate ions, and acetate ions, with nitrate ions being preferred. The amounts of cerium, zirconium, and lanthanum salts, based on their oxides, can be 20–60:20–60:5–30, preferably 40–45:40–45:10–20.

[0050] The alkaline solution is an aqueous solution of ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, preferably ammonia solution, and more preferably 15-25% ammonia solution. The amount of alkaline substances such as ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate used is 2 to 12 times the molar amount of metal ions in the metal salt solution, preferably 5 to 10 times.

[0051] The grinding beads may include large beads with a diameter of 14-30 mm and small beads with a diameter of 6-13 mm, wherein the diameter ratio of the large beads to the small beads is greater than 1.4 and the volume ratio is greater than 2. Preferably, the large beads have a diameter of 16-20 mm, the small beads have a diameter of 8-12 mm, and the diameter ratio of the large beads to the small beads is between 1.5 and 2.0, and the volume ratio is between 2.5 and 4.0.

[0052] The dispersant is selected from at least one of ethylene glycol, propylene glycol, polyethylene glycol, and polyethylene glycol monomethyl ether, preferably polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 800, and polyethylene glycol 1000. The amount of dispersant used is 5-20% of the total amount of copper, nickel, and lanthanum oxides, preferably 10-15%.

[0053] The coating amount in step 4 is 40–160 g / L, preferably 50–80 g / L.

[0054] The roasting temperature in step 4 is 540–600°C, preferably 570–590°C.

[0055] In one implementation, in step 5:

[0056] The La2O3-ZrO2 contains 1-5 wt% La2O3, preferably 3-4 wt%. The mass ratio of La2O3-ZrO2 to the lower cerium-zirconium solid solution is 1:2-6, preferably 1:3-5.

[0057] The amount of rhodium salt solution, calculated as rhodium oxide, is 0.1% to 1% of the total amount of La2O3-ZrO2 and cerium-zirconium solid solution, preferably 0.2% to 0.5%.

[0058] The coating amount in step 5 is 30-120 g / L, preferably 70-100 g / L.

[0059] The roasting temperature in step 5 is 560–620°C, preferably 590–610°C.

[0060] In one embodiment, the palladium content in the lower coating of the prepared three-way catalyst is 10–60 g / ft. 3 Preferably 15–40 g / ft 3 The rhodium content in the top coating is 1–25 g / ft. 3 Preferably 1-10 g / ft 3 .

[0061] Another method of the present invention provides a ternary catalyst comprising a lower coating, a middle coating, and an upper coating, wherein in the lower coating, palladium is supported on La2O3-ZrO2 and a lower cerium-zirconium solid solution; the middle coating is a Cu-Ni-La solid solution; and the upper coating is rhodium supported on La2O3-ZrO2 and an upper cerium-zirconium solid solution.

[0062] In one embodiment, the ternary catalyst is prepared by the method according to the invention.

[0063] In one embodiment, the palladium content in the lower coating is 10–60 g / ft. 3 Preferably 15–40 g / ft 3 The rhodium content in the top coating is 1–25 g / ft. 3 Preferably 1-10 g / ft 3 .

[0064] In one embodiment, in the lower coating layer, the La2O3 content in the La2O3-ZrO2 is 1-5 wt%, preferably 3-4 wt%. The mass ratio of La2O3-ZrO2 to the lower cerium-zirconium solid solution is 0.8-1.5:1, preferably 0.9-1.1:1. The lower cerium-zirconium solid solution comprises cerium oxide, zirconium oxide, and rare earth element oxides. The rare earth element is selected from at least one of La, Y, Pr, and Nd, preferably Y and La. The mass ratio of cerium oxide, zirconium oxide, and rare earth element oxides is 20-60:30-70:5-25. In a preferred embodiment, the rare earth element is selected from Y and La, and the mass ratio of cerium oxide, zirconium oxide, and rare earth element oxides is CeO2:ZrO2:Y2O3:La2O3 = 30-40:45-55:10-15:5-10, preferably 40:45:10:5 and 30:55:10:5.

[0065] In one embodiment, in the upper coating layer, the La2O3 content in the La2O3-ZrO2 is 1-5 wt%, preferably 3-4 wt%. The mass ratio of La2O3-ZrO2 to the upper cerium-zirconium solid solution is 1:2-6, preferably 1:3-5. The upper cerium-zirconium solid solution comprises cerium oxide, zirconium oxide, and rare earth element oxides. The rare earth element is selected from at least one of La, Y, Pr, and Nd, preferably Y and La. The mass ratio of cerium oxide, zirconium oxide, and rare earth element oxides is 20-60:30-70:5-25. In a preferred embodiment, the rare earth element is selected from Y and La, and the mass ratio of cerium oxide, zirconium oxide, and rare earth element oxides is CeO2:ZrO2:Y2O3:La2O3 = 30-40:35-50:5-10:10-15, preferably 40:45:5:10 and 35:50:5:10.

[0066] Beneficial effects:

[0067] This invention provides a three-way catalyst for enhanced automotive exhaust purification. The catalyst comprises three coatings: a lower coating of palladium supported on a La₂O₃-ZrO₂ and cerium-zirconium solid solution; a middle coating of Cu-Ni-La solid solution, acting as a physical barrier to isolate palladium and rhodium; and an upper coating of rhodium supported on a La₂O₃-ZrO₂ and cerium-zirconium solid solution. This three-way catalyst exhibits enhanced CO, NOx, and HC conversion capabilities, making it suitable for use in automotive exhaust purification. Detailed Implementation

[0068] The following will describe preferred embodiments of the invention in detail. These embodiments are provided to better illustrate the invention and are not intended to limit the invention to these examples. Non-essential improvements and adjustments to the embodiments based on the invention's description still fall within the scope of the invention.

[0069] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0070] Preparation Example 1: Preparation of Lower Cerium-Zirconium Solid Solution

[0071] Cerium nitrate, zirconium nitrate, yttrium nitrate, and lanthanum nitrate were each prepared into 2 mol / L solutions. These solutions were then mixed in an oxide weight ratio of CeO2:ZrO2:Y2O3:La2O3 = 40:45:10:5. Pure water was added to prepare 100 L of a mixed solution with a total metal ion concentration of approximately 0.72 mol / L. 1.5 kg of the surfactant lauroyl N-n-propylglucamide was added and stirred until homogeneous, yielding a metal ion solution. 40 L of a 25% ammonia solution was taken, and 60 L of 16 mm diameter polytetrafluoroethylene (PTFE) grinding beads and 20 L of 10 mm diameter PTFE grinding beads were added, with continuous stirring. The metal ion solution was then added to the ammonia solution over 30 min, with continuous stirring to obtain a suspension. After filtering out the grinding beads, 1 kg of the dispersant hexadecyltrimethylammonium bromide was added to the suspension, and stirring was continued for 30 min to obtain a precipitate. The precipitate was collected by pressure filtration, washed three times with pure water, dried at 120°C for 8 hours, and then calcined in a muffle furnace at 680°C for 5 hours. After sieving, the lower layer of cerium-zirconium solid solution was obtained.

[0072] Preparation Example 2: Preparation of Lower Cerium-Zirconium Solid Solution

[0073] Cerium nitrate, zirconium nitrate, yttrium nitrate, and lanthanum nitrate were each prepared into 2 mol / L solutions. These solutions were then mixed in an oxide weight ratio of CeO2:ZrO2:Y2O3:La2O3 = 30:55:10:5. Pure water was added to prepare 100 L of a mixed solution with a total metal ion concentration of approximately 0.74 mol / L. 1 kg of the surfactant lauroyl N-n-propylglucamide was added and stirred until homogeneous, yielding a metal ion solution. 40 L of a 25% ammonia solution was taken, and 60 L of 16 mm diameter polytetrafluoroethylene (PTFE) grinding beads and 20 L of 10 mm diameter PTFE grinding beads were added, with continuous stirring. The metal ion solution was then added to the ammonia solution over 30 min, with continuous stirring to obtain a suspension. After filtering out the grinding beads, 1 kg of the dispersant hexadecyltrimethylammonium bromide was added to the suspension, and stirring was continued for 30 min to obtain a precipitate. The precipitate was collected by pressure filtration, washed three times with pure water, dried at 120°C for 8 hours, and then calcined in a muffle furnace at 680°C for 5 hours. After sieving, the lower layer of cerium-zirconium solid solution was obtained.

[0074] Preparation Example 3: Preparation of Upper Cerium-Zirconium Solid Solution

[0075] Cerium nitrate, zirconium nitrate, yttrium nitrate, and lanthanum nitrate were each prepared into 2 mol / L solutions. These solutions were then mixed in an oxide weight ratio of CeO2:ZrO2:Y2O3:La2O3 = 40:45:5:10. Pure water was added to prepare 100 L of a mixed solution with a total metal ion concentration of approximately 0.70 mol / L. 1.5 kg of the surfactant lauroyl N-n-propylglucamide was added and stirred until homogeneous, yielding a metal ion solution. 40 L of a 25% ammonia solution was taken, and 60 L of 16 mm diameter polytetrafluoroethylene (PTFE) grinding beads and 20 L of 10 mm diameter PTFE grinding beads were added, with continuous stirring. The metal ion solution was then added to the ammonia solution over 30 min, with continuous stirring to obtain a suspension. After filtering out the grinding beads, 1 kg of the dispersant hexadecyltrimethylammonium bromide was added to the suspension, and stirring was continued for 30 min to obtain a precipitate. The precipitate was collected by pressure filtration, washed three times with pure water, dried at 120°C for 8 hours, and then calcined in a muffle furnace at 680°C for 5 hours. After sieving, the upper cerium-zirconium solid solution was obtained.

[0076] Preparation Example 4: Preparation of Upper Cerium-Zirconium Solid Solution

[0077] Cerium nitrate, zirconium nitrate, yttrium nitrate, and lanthanum nitrate were each prepared into 2 mol / L solutions. These solutions were then mixed in an oxide weight ratio of CeO2:ZrO2:Y2O3:La2O3 = 35:50:5:10. Pure water was added to prepare 100 L of a mixed solution with a total metal ion concentration of approximately 0.71 mol / L. 1.5 kg of the surfactant lauroyl N-n-propylglucamide was added and stirred until homogeneous, yielding a metal ion solution. 40 L of a 25% ammonia solution was taken, and 60 L of 16 mm diameter polytetrafluoroethylene (PTFE) grinding beads and 20 L of 10 mm diameter PTFE grinding beads were added, with continuous stirring. The metal ion solution was then added to the ammonia solution over 30 min, with continuous stirring to obtain a suspension. After filtering out the grinding beads, 1 kg of the dispersant hexadecyltrimethylammonium bromide was added to the suspension, and stirring was continued for 30 min to obtain a precipitate. The precipitate was collected by pressure filtration, washed three times with pure water, dried at 120°C for 8 hours, and then calcined in a muffle furnace at 680°C for 5 hours. After sieving, the upper cerium-zirconium solid solution was obtained.

[0078] Comparative Preparation Example 1: Preparation of Lower Cerium-Zirconium Solid Solution

[0079] Similar to Preparation Example 1, except that the metal ion solution was first added to ammonia water, and after the reaction was completed, it was ball-milled with 60L polytetrafluoroethylene (PTFE) grinding beads with a diameter of 16mm and 20L polytetrafluoroethylene (PTFE) grinding beads with a diameter of 10mm.

[0080] Comparative Preparation Example 2: Preparation of Upper Cerium-Zirconium Solid Solution

[0081] Similar to Preparation Example 2, except that the metal ion solution was first added to ammonia water, and after the reaction was completed, it was ball-milled with 60L polytetrafluoroethylene (PTFE) grinding beads with a diameter of 16mm and 20L polytetrafluoroethylene (PTFE) grinding beads with a diameter of 10mm.

[0082] The particle size distribution and specific surface area of ​​the above-mentioned cerium-zirconium solid solution are shown in Table 1 below.

[0083] Table 1:

[0084]

[0085]

[0086] Example 1: Preparation of a three-way catalyst

[0087] Step 1, coating of the lower coating: 1 kg of La2O3-ZrO3 with a La2O3 content of 3% was ball-milled to a particle size of 5-15 μm, and then added to pure water along with 1 kg of cerium-zirconium solid solution from Preparation Example 1 and stirred evenly. Then, 50 g of palladium nitrate solution (1 mol / L) was added dropwise, and the solution was coated onto the honeycomb support at a coating amount of 130 g / L. The solution was dried at 110 °C for 5 h, and then placed in a muffle furnace and calcined at 550 °C for 2 h to obtain a catalyst semi-finished product coated with the lower coating.

[0088] Step 2, Coating of the intermediate coating: Prepare 2 mol / L solutions of copper nitrate, nickel nitrate, and lanthanum nitrate respectively. Take 450g:450g:100g of the oxides CuO, NiO, and La2O3 respectively, mix the above solutions, add pure water to prepare 10L of mixed solution with a total metal ion concentration of approximately 1.23 mol / L, stir evenly to obtain a metal ion solution; take 6.8L of 25% ammonia solution, add 6L of 16mm diameter polytetrafluoroethylene (PTFE) grinding beads and 2L of 10mm diameter grinding beads to it. Milling of PTFE beads (mm) was performed with continuous stirring. Then, metal ion solution was added to ammonia solution within 30 min, and the mixture was stirred continuously to obtain a suspension. After filtering out the milling beads, 100 g of polyethylene glycol 600 was added to the suspension, and the mixture was stirred for another 30 min. The mixture was then coated onto the catalyst semi-finished product with the lower coating prepared in step 1 at a coating amount of 60 g / L. The lower coating was then covered and dried at 110 °C for 5 h. Subsequently, the product was placed in a muffle furnace and calcined at 580 °C for 2 h to obtain the catalyst semi-finished product with the middle and lower coatings.

[0089] Step 3, coating of the upper coating: 600g of La2O3-ZrO3 with a La2O3 content of 3% was ball-milled to a particle size of 5-15μm, and then added to pure water along with 2.4kg of cerium-zirconium solid solution from Preparation Example 2 and stirred evenly. Then, 20g of rhodium nitrate solution (1mol / L) was added dropwise and coated onto the catalyst semi-finished product with the middle and lower coatings prepared in Step 2 at a coating amount of 90g / L. The middle coating was then covered and dried at 110℃ for 5h. Subsequently, it was placed in a muffle furnace and calcined at 600℃ for 2h to obtain the three-way catalyst finished product.

[0090] The Pd content in the lower coating of the finished product is 28.2 g / ft. 3 The Rh content in the top coating is 4.1 g / ft. 3 .

[0091] Example 2: Preparation of a three-way catalyst

[0092] Similar to Example 1, except that the cerium-zirconium solid solutions in steps 1 and 3 are prepared using the lower cerium-zirconium solid solution of Example 3 and the upper cerium-zirconium solid solution of Example 4, respectively; the Pd content in the lower coating layer of the finished product is 30.3 g / ft. 3 The Rh content in the top coating is 4.8 g / ft. 3 .

[0093] Example 3: Preparation of a three-way catalyst

[0094] Step 1, coating of the lower coating: 1 kg of La2O3-ZrO3 with a La2O3 content of 3% was ball-milled to a particle size of 5-15 μm, and then added to pure water along with 1 kg of cerium-zirconium solid solution from Preparation Example 1 and stirred evenly. Then, 50 g of palladium nitrate solution (1 mol / L) was added dropwise, and the solution was coated onto the honeycomb support at a coating amount of 130 g / L. The solution was dried at 110 °C for 5 h, and then placed in a muffle furnace and calcined at 550 °C for 2 h to obtain a catalyst semi-finished product coated with the lower coating.

[0095] Step 2, Coating of the intermediate coating: Prepare 2 mol / L solutions of copper nitrate, nickel nitrate, and lanthanum nitrate respectively. Take 400g, 400g, and 200g of the oxides CuO, NiO, and La2O3 respectively, mix the above solutions, add pure water to prepare 10L of mixed solution with a total metal ion concentration of approximately 1.16 mol / L, stir evenly to obtain a metal ion solution; take 6.8L of 25% ammonia solution, add 6L of 16mm diameter polytetrafluoroethylene (PTFE) grinding beads and 2L of 10mm diameter grinding beads to it. Milling of PTFE beads (mm) was performed with continuous stirring. Then, metal ion solution was added to ammonia solution within 30 min, and the mixture was stirred continuously to obtain a suspension. After filtering out the milling beads, 100 g of polyethylene glycol 600 was added to the suspension, and the mixture was stirred for another 30 min. The mixture was then coated onto the catalyst semi-finished product with the lower coating prepared in step 1 at a coating amount of 60 g / L. The lower coating was then covered and dried at 110 °C for 5 h. Subsequently, the product was placed in a muffle furnace and calcined at 580 °C for 2 h to obtain the catalyst semi-finished product with the middle and lower coatings.

[0096] Step 3, coating of the upper coating: 600g of La2O3-ZrO3 with a La2O3 content of 3% was ball-milled to a particle size of 5-15μm, and then added to pure water along with 2.4kg of cerium-zirconium solid solution from Preparation Example 2 and stirred evenly. Then, 20g of rhodium nitrate solution (1mol / L) was added dropwise and coated onto the catalyst semi-finished product with the middle and lower coatings prepared in Step 2 at a coating amount of 90g / L. The middle coating was then covered and dried at 110℃ for 5h. Subsequently, it was placed in a muffle furnace and calcined at 600℃ for 2h to obtain the three-way catalyst finished product.

[0097] The Pd content in the lower coating of the finished product is 28.3 g / ft. 3 The Rh content in the top coating is 4.0 g / ft. 3 .

[0098] Comparative Example 1:

[0099] Similar to Example 1, except that the lower cerium-zirconium solid solution of Comparative Preparation Example 1 was used instead of the lower cerium-zirconium solid solution of Preparation Example 1, and the upper cerium-zirconium solid solution of Comparative Preparation Example 2 was used instead of the upper cerium-zirconium solid solution of Preparation Example 2.

[0100] Comparative Example 2: Preparation of a Three-Way Catalyst

[0101] Step 1, coating of the lower coating: 1 kg of La2O3-ZrO3 with a La2O3 content of 3% was ball-milled to a particle size of 5-15 μm, and then added to pure water along with 1 kg of cerium-zirconium solid solution from Preparation Example 1 and stirred evenly. Then, 50 g of palladium nitrate solution (1 mol / L) was added dropwise, and the solution was coated onto the honeycomb support at a coating amount of 130 g / L. The solution was dried at 110 °C for 5 h, and then placed in a muffle furnace and calcined at 550 °C for 2 h to obtain a catalyst semi-finished product coated with the lower coating.

[0102] Step 2, Coating of the intermediate coating: Prepare 2 mol / L solutions of copper nitrate and nickel nitrate respectively. Take 500g of CuO and 500g of NiO oxides respectively and mix the above solutions. Add pure water to prepare 10L of mixed solution with a total metal ion concentration of approximately 1.30 mol / L. Stir evenly to obtain a metal ion solution. Take 7L of 25% ammonia solution and add 6L of 16mm diameter polytetrafluoroethylene (PTFE) grinding beads and 2L of 10mm diameter PTFE grinding beads to it. The ball milling beads were stirred continuously. Then, the metal ion solution was added to the ammonia solution within 30 minutes and stirred continuously to obtain a suspension. After filtering out the ball milling beads, 100g of polyethylene glycol 600 was added to the suspension and stirred for another 30 minutes. The suspension was coated onto the catalyst semi-finished product with the lower coating prepared in step 1 at a coating amount of 60g / L. The lower coating was covered and dried at 110℃ for 5 hours. Then, it was placed in a muffle furnace and calcined at 580℃ for 2 hours to obtain the catalyst semi-finished product with the middle and lower coatings.

[0103] Step 3, coating of the upper coating: 600g of La2O3-ZrO3 with a La2O3 content of 3% was ball-milled to a particle size of 5-15μm, and then added to pure water along with 2.4kg of cerium-zirconium solid solution from Preparation Example 2 and stirred evenly. Then, 20g of rhodium nitrate solution (1mol / L) was added dropwise and coated onto the catalyst semi-finished product with the middle and lower coatings prepared in Step 2 at a coating amount of 90g / L. The middle coating was then covered and dried at 110℃ for 5h. Subsequently, it was placed in a muffle furnace and calcined at 600℃ for 2h to obtain the three-way catalyst finished product.

[0104] The Pd content in the lower coating of the finished product is 28.0 g / ft. 3 The Rh content in the top coating is 4.2 g / ft. 3 .

[0105] Test case

[0106] The three-way catalysts prepared in Examples 1-3 and Comparative Examples 1-2 were aged under the same conditions in a high-temperature muffle furnace at 750°C for 24 hours, and then packaged as a purifier. The whole vehicle emissions were tested according to the WLTC cycle. The engine displacement of the test vehicle was 1.6L. The emission test results are shown in Table 2.

[0107] Table 2:

[0108] Three-way catalyst CO (mg / km) NOx (mg / km) THC (mg / km)* Example 1 157.8 24.4 13.2 Example 2 151.1 21.2 12.8 Example 3 143.2 20.5 11.9 Comparative Example 1 214.5 28.8 17.4 Comparative Example 2 205.6 26.7 16.9

[0109] *THC represents the total amount of all hydrocarbons in the gas.

[0110] The results above show that the three-way catalysts of Examples 1-3 of this invention exhibit excellent catalytic performance in converting CO, HC, and NOx, and are capable of purifying automobile exhaust under various transient operating conditions. In contrast, the performance of the three-way catalysts in Comparative Examples 1-2 is somewhat degraded.

[0111] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing a three-way catalyst, comprising: Step 1: Preparation of the lower cerium-zirconium solid solution A metal salt solution is obtained by mixing cerium salt solution, zirconium salt solution and rare earth element salt solution, and then adding the surfactant polyhydroxy fatty acid amide. Add grinding beads to an alkaline solution, and add a metal salt solution dropwise while ball milling. After the addition is complete, continue stirring, then filter out the grinding beads, add a dispersant, filter out the precipitate, wash, dry, calcine, and sieve to obtain a lower layer of cerium-zirconium solid solution; wherein the polyhydroxy fatty acid amide is selected from at least one of lauroyl N-n-propyl glucamide, tridecanoyl N-n-propyl glucamide, and stearoyl N-n-propyl glucamide; the amount of polyhydroxy fatty acid amide used is 10-15% of the total amount of cerium, zirconium, and rare earth element oxides; Step 2: Preparation of the upper cerium-zirconium solid solution A metal salt solution is obtained by mixing cerium salt solution, zirconium salt solution, and rare earth element salt solution, and a surfactant, polyhydroxy fatty acid amide, is added. Ball milling beads are added to an alkaline solution, and the metal salt solution is added dropwise while ball milling. After the addition is complete, stirring continues, and then the ball milling beads are filtered out. A dispersant is added, and the precipitate is filtered out, washed, dried, calcined, and sieved to obtain an upper cerium-zirconium solid solution. The polyhydroxy fatty acid amide is selected from at least one of lauroyl N-n-propyl glucamide, tridecanoyl N-n-propyl glucamide, and stearoyl N-n-propyl glucamide. The amount of polyhydroxy fatty acid amide used is 10-15% of the total amount of cerium, zirconium, and rare earth element oxides. Step 3: Applying the lower coating layer After ball milling La2O3-ZrO2 to a particle size of 5-15 μm, it is added to pure water along with the lower cerium-zirconium solid solution and stirred evenly. Then, palladium salt solution is added dropwise and mixed evenly. The mixture is then coated onto a honeycomb support, dried, and calcined to obtain a catalyst semi-finished product coated with the lower coating. Step 4: Applying the intermediate coating: A copper salt solution, a nickel salt solution, and a lanthanum salt solution are mixed to obtain a metal salt solution. A ball milling bead is added to an alkaline solution, and the metal salt solution is added dropwise while ball milling. After the addition is complete, stirring is continued. The ball milling bead is then filtered out, and a dispersant is added. The mixture is coated onto the catalyst semi-finished product with a lower coating prepared in step 3. The lower coating is then covered, dried, and calcined to obtain a catalyst semi-finished product with a middle and lower coating. Step 5: Applying the upper coating After ball milling La2O3-ZrO2 to a particle size of 5-15 μm, it is added to pure water along with the upper cerium-zirconium solid solution and stirred evenly. Then, a rhodium salt solution is added dropwise and mixed evenly. The mixture is then coated onto the catalyst semi-finished product coated with the middle and lower coatings, covered with the middle coating, dried, and calcined to obtain the three-way catalyst finished product.

2. The preparation method according to claim 1, characterized in that, In step 1: The rare earth element is selected from at least one of La, Y, Pr, and Nd; the amounts of cerium salt, zirconium salt, and rare earth element salt, calculated by their oxides, are 20–60:30–70:5–25. The grinding beads include large beads with a particle size of 14-30 mm and small beads with a particle size of 6-13 mm, and the particle size ratio of the large beads to the small beads is greater than 1.4 and the volume ratio is greater than 2. The dispersant is selected from at least one of dodecyltrimethylammonium bromide, dodecyldimethylbenzylammonium bromide, dodecyltrimethylammonium chloride, dodecyldimethylbenzylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyldimethylbenzylammonium bromide, hexadecyltrimethylammonium chloride, and hexadecyldimethylbenzylammonium chloride; the amount of dispersant used is 1 to 20% of the total amount of cerium, zirconium, and rare earth element oxides.

3. The preparation method according to claim 2, characterized in that, In step 1: The rare earth elements are selected from Y and La. The amounts of cerium salts, zirconium salts, and rare earth element salts, calculated by their oxides, are CeO2:ZrO2:Y2O3:La2O3 = 30~40:45~55:10~15:5~10. The amount of dispersant used is 5-10% of the total amount of cerium, zirconium, and rare earth element oxides.

4. The preparation method according to claim 1, characterized in that, In step 2: The rare earth element is selected from at least one of La, Y, Pr, and Nd; the amounts of cerium salt, zirconium salt, and rare earth element salt, calculated by their oxides, are 20–60:30–70:5–25. The grinding beads include large beads with a particle size of 14-30 mm and small beads with a particle size of 6-13 mm, and the particle size ratio of the large beads to the small beads is greater than 1.4 and the volume ratio is greater than 2. The dispersant is selected from at least one of dodecyltrimethylammonium bromide, dodecyldimethylbenzylammonium bromide, dodecyltrimethylammonium chloride, dodecyldimethylbenzylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyldimethylbenzylammonium bromide, hexadecyltrimethylammonium chloride, and hexadecyldimethylbenzylammonium chloride; the amount of dispersant used is 1 to 20% of the total amount of cerium, zirconium, and rare earth element oxides.

5. The preparation method according to claim 4, characterized in that, In step 2: The rare earth elements are selected from Y and La. The amounts of cerium salts, zirconium salts, and rare earth element salts, calculated by their oxides, are CeO2:ZrO2:Y2O3:La2O3 = 30~40:35~50:5~10:10~15. The amount of dispersant used is 5-10% of the total amount of cerium, zirconium, and rare earth element oxides.

6. The preparation method according to claim 1, characterized in that, In step 3: In the La2O3-ZrO2, the content of La2O3 is 1-5 wt%; the mass ratio of La2O3-ZrO2 to the lower cerium-zirconium solid solution is 0.8-1.5:1; The amount of palladium salt solution, calculated as palladium oxide, is 0.5% to 3% of the total amount of La2O3-ZrO2 and cerium-zirconium solid solution; The coating amount in step 3 is 50–240 g / L.

7. The preparation method according to claim 6, characterized in that, In step 3: In the La2O3-ZrO2, the content of La2O3 is 3-4 wt%; the mass ratio of La2O3-ZrO2 to the lower cerium-zirconium solid solution is 0.9-1.1:1; The amount of palladium salt solution, calculated as palladium oxide, is 1-2% of the total amount of La2O3-ZrO2 and cerium-zirconium solid solution; The coating amount in step 3 is 100-160 g / L.

8. The preparation method according to claim 1, characterized in that, In step 4: The amounts of cerium salts, zirconium salts, and lanthanum salts, based on their oxides, are 20–60: 20–60: 5–30. The grinding beads include large beads with a particle size of 14-30 mm and small beads with a particle size of 6-13 mm, and the particle size ratio of the large beads to the small beads is greater than 1.4 and the volume ratio is greater than 2. The dispersant is selected from at least one of ethylene glycol, propylene glycol, polyethylene glycol, and polyethylene glycol monomethyl ether; the amount of dispersant used is 5-20% of the total amount of copper, nickel, and lanthanum oxides. The coating amount in step 4 is 40–160 g / L.

9. The preparation method according to claim 8, characterized in that, In step 4: The amounts of cerium salts, zirconium salts, and lanthanum salts, based on their oxides, are 40–45:40–45:10–20; The dispersant is selected from polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 800, and polyethylene glycol 1000; The amount of dispersant used is 10-15% of the total amount of copper, nickel, and lanthanum oxides; The coating amount in step 4 is 50-80 g / L.

10. The preparation method according to claim 1, characterized in that, In step 5: In the La2O3-ZrO2, the content of La2O3 is 1-5 wt%; the mass ratio of La2O3-ZrO2 to the lower cerium-zirconium solid solution is 1:2-6; The amount of rhodium salt solution, calculated as rhodium oxide, is 0.1% to 1% of the total amount of La2O3-ZrO2 and cerium-zirconium solid solution; The coating amount in step 5 is 30-120 g / L.

11. The preparation method according to claim 10, characterized in that, In step 5: In the La2O3-ZrO2, the content of La2O3 is 3-4 wt%; the mass ratio of La2O3-ZrO2 to the lower cerium-zirconium solid solution is 1:3-5; The amount of rhodium salt solution, calculated as rhodium oxide, is 0.2% to 0.5% of the total amount of La2O3-ZrO2 and cerium-zirconium solid solution; The coating amount in step 5 is 70-100 g / L.

12. A ternary catalyst comprising a lower coating, a middle coating, and an upper coating, wherein in the lower coating, palladium is supported on La2O3-ZrO2 and a lower cerium-zirconium solid solution; the middle coating is a Cu-Ni-La solid solution; and the upper coating is rhodium supported on La2O3-ZrO2 and an upper cerium-zirconium solid solution, wherein the ternary catalyst is prepared by the method according to any one of claims 1-11.

13. The three-way catalyst according to claim 12, characterized in that, The palladium content in the lower coating is 10–60 g / ft. 3 The rhodium content in the top coating is 1–25 g / ft. 3 .

14. The three-way catalyst according to claim 12, characterized in that, The palladium content in the lower coating is 15–40 g / ft. 3 The rhodium content in the top coating is 1–10 g / ft. 3 .

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