LNT catalyst and preparation method thereof

Abstract

This invention discloses a LNT catalyst and its preparation method. The catalyst comprises a honeycomb ceramic support with a metal oxide composite coating on the inner wall of the honeycomb pores. The composite coating comprises a first catalytic coating, a second catalytic coating, and a third catalytic coating. The first catalytic coating comprises 50% platinum supported on a cerium-magnesium-aluminum composite oxide and 50% platinum supported on a cerium-barium-aluminum composite oxide; the second catalytic coating comprises palladium supported on a barium-cerium composite oxide, with a barium-cerium molar ratio of 1:9 to 1:3; and the third catalytic coating comprises rhodium supported on a barium-zirconium-aluminum composite oxide, with a barium-zirconium molar ratio of 1:1 to 1:2 and a barium-aluminum molar ratio of 1:1 to 1:9. The first coating, with platinum supported on the cerium-magnesium-aluminum and cerium-barium-aluminum composite oxides, improves the catalyst's NOx storage capacity and conversion efficiency, achieving better performance than platinum supported solely on cerium-aluminum, cerium-magnesium-aluminum, or cerium-barium-aluminum. Furthermore, the three-layer coating design improves catalyst durability.

Description

Technical Field

[0001] The present invention relates to the technical field of diesel vehicle engine exhaust purification catalysts, and in particular to an LNT catalyst and a preparation method thereof. Background Art

[0002] Lean-burn diesel vehicles offer high fuel economy, but their exhaust contains relatively high levels of nitrogen oxides. Currently, the mainstream treatment methods are selective catalytic reduction (SCR) and lean NOx trapping (LNT). Diesel vehicles include both light-duty and heavy-duty diesel vehicles. Heavy-duty diesel vehicles emit higher concentrations of nitrogen oxides, and to convert them into non-polluting gases such as carbon dioxide, water, and nitrogen, a variety of catalyst systems are used in the vehicle's exhaust system to form an exhaust after-treatment system.

[0003] Among them, the LNT catalyst has the advantages of not requiring additional urea and frequent maintenance. The actual working condition of the LNT is a periodic lean-burn and rich-burn cycle, usually with a lean-burn (λ﹥1) stage of about 2 minutes. In this process, NOx reacts with the catalyst to capture or physically adsorb, and then enters a rich-burn stage (λ<1) for 3-5 seconds. The captured and adsorbed NOx and reducing gases such as CO and HC in the exhaust gas are reduced to gases such as N2.

[0004] Existing LNT catalysts suffer from low NOx capture efficiency, susceptibility to sulfur poisoning, and precious metal agglomeration and aging. Over time, NOx capture efficiency declines. This invention simultaneously introduces different alkaline earth metals into the first and third catalytic coatings of the LNT catalyst, using different precious metal loading methods. This improves the NOx capture efficiency and durability of the LNT catalyst, thereby extending its service life. Summary of the Invention

[0005] The object of the present invention is to provide a LNT catalyst and a preparation method thereof, so as to solve the problems caused by the prior art.

[0006] A LNT catalyst and a preparation method thereof include a honeycomb ceramic support, wherein the inner wall of the pores of the honeycomb ceramic support is coated with a metal oxide composite coating, wherein the metal composite coating includes a first catalytic coating, a second catalytic coating, and a third catalytic coating. The surface of the first catalytic coating is coated with the second catalytic coating, and the surface of the second catalytic coating is coated with the third catalytic coating.

[0007] A catalytic coating layer comprising 50% platinum supported on a cerium-magnesium-aluminum composite oxide, with a cerium-magnesium molar ratio of 1:1 to 1:2 and a cerium-aluminum molar ratio of 1:3 to 1:10; and 50% platinum supported on a cerium-barium composite oxide, with a cerium-barium molar ratio of 1:1 to 1:2 and a cerium-aluminum molar ratio of 1:3 to 1:10;

[0008] The second catalytic coating is composed of palladium supported on a composite oxide with a molar ratio of barium to cerium of 1:9 to 1:3;

[0009] The three catalytic coatings are composed of rhodium supported on barium-zirconium-aluminum composite oxides, wherein the molar ratio of barium-zirconium is 1:1-1:2, and the molar ratio of barium-aluminum is 1:1-1:9.

[0010] Preferably, the metal composite coating is three-layered;

[0011] The total weight gain of the metal oxide composite coating ranges from 150 to 400 g / L;

[0012] One of the catalytic coating weight gain ranges from 50 to 150 g / L;

[0013] The weight gain of the second catalytic coating ranges from 50 to 150 g / L;

[0014] The weight gain of the three catalytic coatings ranges from 50 to 150 g / L.

[0015] Preferably, the metal oxide composite coating contains precious metals, and the types of precious metals are platinum, palladium, and rhodium.

[0016] Preferably, the precious metal content is 20 g / ft3 to 200 g / ft3 of the total amount of platinum, palladium and rhodium;

[0017] The platinum-palladium mixing ratio is 10:1 to 1:1;

[0018] The platinum-rhodium mixing ratio is 10:1 to 1:1.

[0019] Preferably, the noble metal contained in the catalytic coating is platinum or platinum-palladium;

[0020] The precious metal contained in the second catalytic coating is palladium or platinum palladium;

[0021] The three catalytic coatings contain precious metals such as rhodium or platinum rhodium.

[0022] Preferably, the metal oxide composite coating bottom layer also uses platinum, and the platinum is simultaneously loaded on cerium magnesium aluminum and cerium barium aluminum.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. By using platinum loaded on cerium magnesium aluminum and cerium barium aluminum respectively, the performance is better than that of platinum loaded alone on cerium aluminum, platinum loaded alone on cerium magnesium aluminum, and platinum loaded alone on cerium barium aluminum. This shows that after the introduction of magnesium and barium into the bottom layer of the catalytic coating, the metal oxides thereof can act as catalytic promoters to accelerate the conversion of NO to NO2, thereby increasing the storage capacity of NOx and the NOx capture efficiency of the LNT catalyst, while also improving the aging durability of the LNT catalyst. The metal oxides can act as catalysts to accelerate the conversion of NO to NO2. During the test, the LNT catalyst was operated at a constant space velocity, storing NOx for a longer lean burn time and reducing NOx to N2 during a shorter rich burn time. Due to the use of transient switching and constant space velocity, the response speed was fast and the test results were accurate.

[0025] 2. According to another embodiment variant, the starting value of the regeneration parameter can be set based on a set of conditions including the properties of the catalyst material, the LNT temperature used to describe the regeneration capacity of each LNT, the capacity for nitrogen oxide storage, and the mass flow rate of nitrogen oxides in the exhaust gas. Advantageously, the value of the regeneration parameter can be continuously adjusted to the current aging state of the LNT catalyst, making the above-mentioned advantages more obvious. By designing the precious metal catalyst coating, the active temperature range of the catalyst is expanded, and the selection of an appropriate reaction temperature will help extend the life of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the overall three-dimensional structure of the present invention.

[0027] Figure 2 This is a schematic diagram of fresh state comparison data in the present invention.

[0028] Figure 3 Schematic diagram of the NOx storage capacity in the fresh state in the present invention.

[0029] Figure 4 This is a schematic diagram of aging test data in the present invention.

[0030] Figure 5 Schematic diagram of NOx storage capacity in the aging state in the present invention.

[0031] Figure 6 Schematic diagram of the catalyst manufacturing process in the present invention.

[0032] Figure 7 Schematic diagram of the comparative experiment process in the present invention.

[0033] Figure 8 It is a schematic front cross-sectional view of the honeycomb ceramic carrier in the present invention.

[0034] in:

[0035] 1. Honeycomb ceramic carrier; 2. Catalytic composite layer; 3. First catalytic layer; 4. Second catalytic layer; 5. Third catalytic layer. DETAILED DESCRIPTION

[0036] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0037] like Figures 1 to 8 As shown, an LNT catalyst and its preparation method include a honeycomb ceramic substrate 1, wherein the honeycomb pore surface of the honeycomb ceramic substrate 1 is coated with a metal composite coating 2, wherein the metal oxide composite coating 2 includes a first catalytic coating 3, a second catalytic coating 4 and a third catalytic coating 5, wherein the first catalytic coating 3 is coated with the second catalytic coating 4, and the second catalytic coating 4 is coated with the third catalytic coating 5.

[0038] The first catalytic coating 3 is composed of 50% platinum supported on a cerium-magnesium-aluminum composite oxide, with a cerium-magnesium molar ratio of 1:1 to 1:2 and a cerium-aluminum molar ratio of 1:3 to 1:10; and 50% platinum supported on a cerium-barium composite oxide, with a cerium-barium molar ratio of 1:1 to 1:2 and a cerium-aluminum molar ratio of 1:3 to 1:10; the second catalytic coating 4 is composed of palladium supported on a composite oxide with a barium-cerium molar ratio of 1:9 to 1:3; the third catalytic coating 5 is composed of rhodium supported on a barium-zirconium-aluminum composite oxide, with a barium-zirconium molar ratio of 1:1 to 1:2 and a barium-aluminum molar ratio of 1:1 to 1:9. The convenient selection of a suitable reaction temperature will help extend the life of the catalyst.

[0039] In this embodiment, the metal oxide composite coating 2 is three-layered; the total weight gain range of the metal oxide composite coating 2 is 150 to 400 g / L; the weight gain range of the first catalytic coating 3 is 50 to 150 g / L; the weight gain range of the second catalytic coating 4 is 50 to 150 g / L; the weight gain range of the third catalytic coating 5 is 50 to 150 g / L, which expands the active temperature range of the catalyst.

[0040] In this embodiment, the metal oxide composite coating 2 contains precious metals, and the types of precious metals are platinum, palladium, and rhodium, which facilitates the reduction of NOx into N2 in a shorter rich combustion time.

[0041] In this embodiment, the precious metal content is 20g / ft 3 ~200g / ft 3 ; The mixing ratio of platinum and palladium is 10:1 to 1:1; the mixing ratio of platinum and rhodium is 10:1 to 1:1. Metal oxides can be used as catalysts to accelerate the conversion of NO to NO2.

[0042] In this embodiment, the precious metal types contained in the first catalytic coating 3 are platinum or platinum-palladium; the precious metal types contained in the second catalytic coating 4 are palladium or platinum-palladium; and the precious metal types contained in the third catalytic coating 5 are rhodium or platinum-rhodium.

[0043] In this embodiment, the bottom layer of the metal oxide composite coating 2 also uses platinum, and the platinum is simultaneously loaded on cerium magnesium aluminum and cerium barium aluminum, thereby increasing the NOx storage capacity and improving the NOx capture efficiency of the LNT catalyst.

[0044] The LNT catalyst ratio examples are as follows:

[0045] Catalyst-catalytic coating 380g / ft 3 Pt+CeAl secondary catalytic coating 410g / ft 3 Pd+CeBa triple catalytic coating 510g / ft 3 Rh+BaZrAl;

[0046] Implementation Case 2

[0047] Catalyst-catalytic coating 380g / ft 3 Pt+CeBaAl secondary catalytic coating 410g / ft 3 Pd+CeBa triple catalytic coating 510g / ft 3 Rh+BaZrAl;

[0048] Implementation Case 3

[0049] Catalyst-catalytic coating 380g / ft 3 Pt+CeMgAL secondary catalytic coating 410g / ft 3 Pd+CeBa triple catalytic coating 510g / ft 3 Rh+BaZrAl;

[0050] Implementation Case 4

[0051] Catalyst-catalytic coating 340g / ft 3 Pt+CeBaAl&40g / ft 3 Pt+CeMgAl secondary catalytic coating 410g / ft 3 Pd+CeBa triple catalytic coating 510g / ft 3 Rh+BaZrAl;

[0052] Implementation Case 5

[0053] Catalyst-catalytic coating 340g / ft 3 Pt+CeBaAl&40g / ft 3 Pt+CeMgAl secondary catalytic coating 410g / ft 3Pd+CeBa&10g / ft 3 Rh+BaZrAl.

[0054] according to Figure 2 and Figure 3 As shown, the fresh test results are as follows;

[0055] 1. Example Fresh state test results show that the performance of the first layer using platinum loaded on cerium magnesium aluminum and cerium barium aluminum is better than that of platinum loaded on cerium aluminum, which indicates that the introduction of magnesium and barium in the first layer increases the NOx storage capacity.

[0056] 2. The fresh state test results of the examples show that Example 4, in which the first layer of platinum is loaded on cerium magnesium aluminum and cerium barium aluminum respectively, has the largest NOx storage capacity in each temperature range, which indicates that the simultaneous introduction of magnesium and barium significantly increases the NOx storage capacity.

[0057] 3. Example The test results of the fresh state show that the NOx storage capacity of the two-layer coating is smaller than that of the three-layer coating.

[0058] 4. Example Fresh state test results show that when the first layer is made of platinum loaded on cerium magnesium aluminum or cerium barium aluminum, the NOx storage capacity results are relatively close.

[0059] according to Figure 4 and Figure 5 As shown, the aging test is carried out according to the aging method in HJ-451-20087.3.2;

[0060] 1. The test results of the aging state of the embodiment show that the performance of the first layer using platinum loaded on cerium magnesium aluminum and cerium barium aluminum is better than that of platinum loaded on cerium aluminum, which indicates that the introduction of magnesium and barium in the first layer increases the NOx storage capacity;

[0061] 2. The test results of the embodiment in the aged state show that the NOx storage performance of the three-layer coating in the aged state is better than that of the two-layer coating in the aged state;

[0062] 3. The results of the aging test of the examples show that Example 4, in which the first layer of platinum is loaded on cerium magnesium aluminum and cerium barium aluminum, respectively, has the highest NOx storage capacity in all temperature ranges. This indicates that the simultaneous introduction of magnesium and barium also exhibits the highest NOx storage capacity in the aging state.

[0063] 4. The aging test results of the embodiment show that when the first layer is made of platinum loaded on cerium magnesium aluminum or cerium barium aluminum, the NOx storage capacity results are relatively close.

[0064] The comparison of LNT catalyst examples is as follows:

[0065] The practical application of this LNT catalyst and its preparation method includes the following work contents:

[0066] Implementation steps

[0067] Step 1: Platinum, palladium, and rhodium are loaded on cerium-magnesium-aluminum composite oxide, cerium-barium-aluminum composite oxide, barium-zirconium-aluminum composite oxide, and cerium-barium composite oxide in a certain proportion to prepare slurries, which are then coated on supports in a certain order, dried, and calcined to obtain LNT catalysts.

[0068] Step 2:

[0069] Preparation of cerium-magnesium-aluminum composite oxide: Cerium nitrate, magnesium nitrate, and γ-alumina were immersed in equal volumes at a cerium-magnesium molar ratio of 1:1-1:2 and a cerium-aluminum molar ratio of 1:3-1:10 for 24 hours, dried at 120°C for 2 hours, and calcined at 550°C for 2 hours. The mixture was then added to a ball mill for milling, and the D90 was controlled at 8μm-10μm. The slurry was numbered 1.

[0070] Preparation of cerium-barium-aluminum composite oxide: Cerium nitrate, barium acetate, and γ-alumina with a cerium-barium molar ratio of 1:11:2 and a cerium-aluminum molar ratio of 1:3-1:10 were immersed in equal volumes for 24 hours, dried at 120°C for 2 hours, and calcined at 550°C for 2 hours. The mixture was then added to a ball mill for milling, with the D90 value controlled at 8μm-10μm. The slurry was numbered 2.

[0071] Preparation of barium-cerium composite oxide: Barium acetate and cerium nitrate were mixed in a molar ratio of 1:9 to 1:3 and immersed in equal volumes for 24 hours, dried at 120°C for 2 hours, and calcined at 550°C for 2 hours. The mixture was then added to a ball mill for milling, with the D90 value controlled at 8 μm to 10 μm. The slurry was numbered 3.

[0072] Preparation of zirconium-barium-aluminum composite oxide: Barium-zirconium molar ratio of 1:1-1:2, barium-aluminum molar ratio of 1:1-1:9, equal volumes are immersed for 24 hours, dried at 120°C for 2 hours, calcined at 550°C for 2 hours, and then added to a ball mill for ball milling. D90 is controlled at 8μm-10μm, and the slurry is numbered 4.

[0073] Step 3:

[0074] Draw 40g / ft3 of platinum nitrate solution, add it to the ball-milled slurry 1 and stir for 2 hours. Adjust the pH value to 3-7 with nitric acid or acetic acid. Number this slurry 5.

[0075] Draw 40g / ft3 of platinum nitrate solution, add it to the ball-milled slurry 2 and stir for 2 hours, then adjust the pH value to 3-7 with nitric acid or acetic acid. This is numbered as slurry 6.

[0076] Draw 10 g / ft3 of palladium nitrate solution and add it to the ball-milled slurry 3, stirring for 2 hours. Adjust the pH value to 3-7 with nitric acid or acetic acid. Number the slurry 7.

[0077] Extract 10g / ft3 rhodium nitrate solution and add it to slurry 4 and stir for 2h. Adjust the pH value to 3-7 with nitric acid or acetic acid. Number it as slurry 8.

[0078] Step 4:

[0079] The prepared slurry 5 and slurry 6 were mixed, and a binder and a thickener were added to adjust the viscosity to 1000-4000 mPa / s, the solid content to 25%-45%, and the pH value to 3-7. After uniform stirring for 2 hours, the mixture was applied on a honeycomb ceramic carrier, dried at 120°C for 2 hours, and calcined at 550°C to obtain a coating.

[0080] The prepared slurry 7 was added with a binder and a thickener, the viscosity was adjusted to 1000-4000 mPa / s, the solid content was adjusted to 25%-45%, and the pH value was adjusted to 3-7. After uniform stirring for 2 hours, the slurry was applied on the first catalytic coating of the ceramic carrier, dried at 120°C for 2 hours, and calcined at 550°C to obtain the second coating.

[0081] Add binder and thickener to the prepared slurry 8, adjust the viscosity to 1000-4000 MPa / s, adjust the solid content to 25%-45%, adjust the pH value to 3-7, stir evenly for 2 hours, and then apply it on the second catalytic coating of the ceramic carrier, dry it at 120°C for 2 hours, and calcine it at 550°C to obtain the third coating.

[0082] Therefore, the embodiments disclosed above are only illustrative in all aspects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims

1. A LNT catalyst, comprising a honeycomb ceramic carrier (1), wherein the interior of the pores of the honeycomb ceramic carrier (1) is coated with a metal oxide composite coating (2), wherein the metal oxide composite coating (2) comprises a first catalytic coating (3), a second catalytic coating (4) and a third catalytic coating (5), wherein the surface of the first catalytic coating (3) is coated with the second catalytic coating (4), and the surface of the second catalytic coating (4) is coated with the third catalytic coating (5), characterized in that: A catalytic coating (3) is composed of 50% platinum supported on a cerium-magnesium-aluminum composite oxide, with a cerium-magnesium molar ratio of 1:1 to 1:2 and a cerium-aluminum molar ratio of 1:3 to 1:10; and 50% platinum supported on a cerium-barium-aluminum composite oxide, with a cerium-barium molar ratio of 1:1 to 1:2 and a cerium-aluminum molar ratio of 1:3 to 1:10; The second catalytic coating (4) is composed of palladium supported on a composite oxide with a molar ratio of barium to cerium of 1:9 to 1:3; The third catalytic coating (5) is composed of rhodium supported on a barium-zirconium-aluminum composite oxide, wherein the molar ratio of barium to zirconium is 1:1-1:2, and the molar ratio of barium to aluminum is 1:1-1:

9.

2. The LNT catalyst according to claim 1, characterized in that: The metal oxide composite coating (2) is three-layered; The total weight gain of the metal oxide composite coating (2) ranges from 150 to 400 g / L; One of the catalytic coatings (3) has a weight gain range of 50 to 150 g / L; The second catalytic coating (4) has a weight gain range of 50 to 150 g / L; The weight gain range of the third catalytic coating (5) is 50 to 150 g / L.

3. The LNT catalyst according to claim 2, characterized in that: The metal oxide composite coating (2) contains precious metals, and the content of the precious metals is 20g / ft3 to 200g / ft3 of the total amount of platinum, palladium and rhodium; The platinum-palladium mixing ratio is 10:1 to 1:1; The platinum-rhodium mixing ratio is 10:1 to 1:

1.

4. A method for preparing the LNT catalyst according to claim 1, comprising the following steps: Step 1: Platinum, palladium, and rhodium are loaded on cerium-magnesium-aluminum composite oxide, cerium-barium-aluminum composite oxide, barium-zirconium-aluminum composite oxide, and cerium-barium composite oxide in a certain proportion to prepare slurries, which are then coated on supports in a certain order, dried, and calcined to obtain LNT catalysts. Step 2: Preparation of cerium-magnesium-aluminum composite oxide: Cerium nitrate, magnesium nitrate, and γ-alumina were prepared at a cerium-magnesium molar ratio of 1:1-1:2 and a cerium-aluminum molar ratio of 1:3-1:

10. Equal volumes were impregnated for 24 hours, dried at 120°C for 2 hours, and calcined at 550°C for 2 hours. The mixture was then added to a ball mill for milling. The D90 was controlled to be 8 μm-10 μm. This slurry was numbered slurry 1. Preparation of cerium-barium-aluminum composite oxide: Cerium nitrate, barium acetate, and γ-alumina were prepared with a cerium-barium molar ratio of 1:11:2 and a cerium-aluminum molar ratio of 1:3-1:

10. Equal volumes were impregnated for 24 hours, dried at 120°C for 2 hours, and calcined at 550°C for 2 hours. The mixture was then ball milled to control the D90 value to be between 8 μm and 10 μm. This slurry was numbered slurry 2. Preparation of barium-cerium composite oxide: Barium acetate and cerium nitrate were mixed in a molar ratio of 1:9 to 1:3 and immersed in equal volumes for 24 hours, dried at 120°C for 2 hours, and calcined at 550°C for 2 hours. The mixture was then added to a ball mill for milling, with the D90 value controlled at 8 μm to 10 μm. The slurry was numbered 3. Preparation of zirconium-barium-aluminum composite oxide: Barium-zirconium molar ratio of 1:1-1:2, barium-aluminum molar ratio of 1:1-1:9, equal volume impregnation for 24 hours, drying at 120°C for 2 hours, calcining at 550°C for 2 hours, then adding to a ball mill for ball milling, controlling D90 at 8μm-10μm, numbering slurry 4; Step 3: Draw 40g / ft3 of platinum nitrate solution, add it to the ball-milled slurry 1 and stir for 2 hours. Adjust the pH value to 3-7 with nitric acid or acetic acid. Number this slurry 5. Draw 40g / ft3 of platinum nitrate solution, add it to the ball-milled slurry 2 and stir for 2 hours, then adjust the pH value to 3-7 with nitric acid or acetic acid. This is numbered as slurry 6. Draw 10 g / ft3 of palladium nitrate solution and add it to the ball-milled slurry 3, stirring for 2 hours. Adjust the pH value to 3-7 with nitric acid or acetic acid. Number the slurry 7. Extract 10g / ft3 rhodium nitrate solution and add it to slurry 4 and stir for 2h. Adjust the pH value to 3-7 with nitric acid or acetic acid. Number it as slurry 8. Step 4: The prepared slurry 5 and slurry 6 were mixed, a binder and a thickener were added, the viscosity was adjusted to 1000-4000 mPa / s, the solid content was adjusted to 25%-45%, and the pH value was adjusted to 3-7. After uniform stirring for 2 hours, the mixture was applied on a honeycomb ceramic carrier, dried at 120°C for 2 hours, and calcined at 550°C to obtain a coating. The prepared slurry 7 was added with a binder and a thickener to adjust the viscosity to 1000-4000 mPa / s, the solid content to 25%-45%, and the pH value to 3-7. After uniform stirring for 2 hours, the slurry was applied to the first catalytic coating of the ceramic support, dried at 120°C for 2 hours, and calcined at 550°C to obtain the second coating. Add binder and thickener to the prepared slurry 8, adjust the viscosity to 1000-4000 MPa / s, adjust the solid content to 25%-45%, adjust the pH value to 3-7, stir evenly for 2 hours, and then apply it on the second catalytic coating of the ceramic carrier, dry it at 120°C for 2 hours, and calcine it at 550°C to obtain the third coating.

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