A catalyzed gasoline particulate filter and method of making the same

Abstract

The application discloses a catalytic gasoline engine particle trap and a preparation method thereof, and belongs to the technical field of catalyst preparation. The particle trap comprises a particle trap carrier and a coating applied on the carrier; the coating is composed of a first coating and a second coating; the first coating comprises a carrier material and active noble metal, and the coating is distributed along the inner wall of the particle trap; the second coating is composed of one or more of boehmite, alumina, lanthanum-modified alumina, silicon-modified alumina, calcium carbonate and a cerium-zirconium-aluminum compound, has loose and porous and hydrophobic characteristics, is continuously distributed along the filter wall surface of the air inlet channel, effectively fills and fills the openings on the wall surface of the air inlet channel, and effectively improves the fine particulate matter trapping efficiency. The catalytic trap prepared by the application has high initial trapping efficiency for particulate matters with a size of more than 10 nm, the preparation method is easy to operate, accurate to control, has low requirements on equipment, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to catalysts for after-treatment of motor vehicle exhaust, particularly a catalytic gasoline engine particulate filter and its preparation method. Background Technology

[0002] For controlling particulate matter (including particulate mass (PM) and particulate number (PN)) in exhaust gases, gasoline engine particulate filters (GPFs) are considered an effective technology for emission control. Due to its alternating blockage structure at the inlet and outlet of adjacent channels, when engine exhaust gas flows in through the inlet channel, the airflow is blocked on the opposite side, allowing it to exit through pores in the filter wall of the carrier. At this point, the porous inner wall captures particulate matter in the airflow. To simultaneously purify gaseous pollutants, a catalytic coating, i.e., CGPF, is applied. The capture performance of CGPF mainly depends on the synergy between the coating and its carrier structure. Compared to normal temperatures, particulate matter emissions from engines increase significantly under low-temperature conditions (especially 0°C or below); furthermore, Euro VII regulations have explicitly included particulate matter with a PN of 10 nm or larger under regulation. Introducing particulate matter in the 10-23nm range on top of the 23nm requirement will significantly increase particulate matter emissions; this will necessitate CGPF with higher capture efficiency. Although CGPF can increase its particulate matter capture efficiency to some extent during vehicle break-in and mileage, OEMs require CGPF to have high initial capture efficiency in its fresh state or under zero-kilometer conditions, based on vehicle safety risk considerations.

[0003] Therefore, how to achieve gaseous pollutant purification and meet the emission requirements of particulate matter with PN 10nm and above in the future emission regulations through the matching and synergy of coating and GPF carrier, while effectively avoiding excessive increase in back pressure caused by coating, is a difficult problem that needs to be solved by those skilled in the art. Summary of the Invention

[0004] The purpose of this invention is to provide a catalytic gasoline engine particulate filter and its preparation method. The filter purifies gaseous pollutants through a first coating. At the same time, with the help of the synergistic effect of the second coating continuously distributed on the intake channel wall and the first coating, the filter improves the initial capture efficiency of particles larger than 10 nm under limited back pressure, thus meeting the particulate emission requirements.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A catalytic converter for gasoline engines and its preparation method are disclosed. The catalytic converter includes a particulate filter carrier and a coating applied to the carrier. The coating consists of a first coating and a second coating. The first coating contains a carrier material and an active noble metal and is distributed along the inner wall of the particulate filter. The second coating contains one or more of boehmite, alumina, lanthanum-modified alumina, silicon-modified alumina, calcium carbonate, and a cerium-zirconium-aluminum composite. The second coating is continuously distributed along the surface of the intake channel filter wall and has loose, porous, and hydrophobic properties.

[0007] Furthermore, the first coating carrier material comprises one or more of silicon or lanthanum-modified alumina, cerium-zirconium composites, and alkaline earth metal compounds.

[0008] Furthermore, the active noble metal in the first coating is one or more of platinum, palladium, and rhodium.

[0009] Furthermore, the bulk density of the second coating material is 0.1–1 g / cm³. 3 Its BET specific surface area is 10-300 m² 2 / g, with a pore volume of 0.5–1.2 cm³. 3 / g.

[0010] Furthermore, the first coating is distributed along the inner wall of the particulate trap carrier, and the second coating is continuously distributed along the surface of the filter wall of the air intake channel.

[0011] Furthermore, the length of the second coating is 90-100% (relative to the length of the particle trap).

[0012] A method for preparing a catalytic converter for gasoline engines includes the following steps:

[0013] (1) First coating: Cerium-zirconium composite material, alumina and alkaline earth metal compound are added to deionized water and stirred to obtain a suspension slurry; after grinding the slurry, noble metal is loaded to obtain a slurry loaded with noble metal; the viscosity of the slurry loaded with noble metal is adjusted by a regulator to control the solid content of the slurry to be 15-35%; the above slurry is coated on the particle trap carrier by vacuum suction coating method; after drying at 100-120℃, a particle trap catalyst coated with the first coating is obtained.

[0014] (2) Second coating: The second coating material is added to deionized water, stirred, and a viscosity modifier is added to control the solid content of the slurry to 3-20% to obtain the second coating slurry; the second coating slurry is coated along the air inlet end of the particulate filter that has been coated with the first coating by vacuum suction coating method; after drying at 100-130℃, it is calcined at 500-600℃ for 1-4h at a heating rate of 2-5℃ / min to obtain the catalytic gasoline engine particulate filter; or, the second coating is obtained by directly loading the second coating material in the form of an aerosol and then calcining.

[0015] Furthermore, in the preparation step (1), the particle size D90 of the first coating slurry is smaller than the particle trap carrier D10; the loading of the first coating in the preparation step (1) is 30-120 g / L; and the loading of the second coating in the preparation step (2) is 3-30 g / L.

[0016] Furthermore, the regulator is one or more of methyl hydroxyethyl cellulose, aluminum glue, polyethylene glycol, and guar gum.

[0017] The beneficial effects of this invention are as follows:

[0018] The catalytic converter for gasoline engines of this invention comprises a first coating and a second coating. The first coating effectively catalytically purifies gaseous pollutants and is distributed within the wall, effectively reducing the coating's impact on back pressure. The second coating is continuously distributed along the surface of the intake channel filter wall, effectively filling the openings (especially large openings) on the intake channel wall surface, improving the capture efficiency of particles larger than 10 nm. Simultaneously, this coating is loosely porous and hydrophobic, ensuring airflow path and reducing the impact of the outer layer on back pressure, while also reducing or avoiding the reduction in particulate capture efficiency caused by secondary openings formed during coating shrinkage during drying and calcination. The preparation method provided by this invention is easy to operate, precisely controlled, and requires minimal equipment, making it suitable for large-scale industrial production. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the catalyst for the particulate trap of the present invention; in the figure: 1-inlet end wall; 2-outlet end wall; 3-filter wall; 4-first coating; 5-second coating.

[0020] Figure 2 SEM images of the coating distribution of the particulate trap catalysts in Examples 1 and 2.

[0021] Figure 3 Back pressure diagrams of a comparative particle trap and a particle trap according to an embodiment of the present invention.

[0022] Figure 4 The particle collection efficiency (PN-23nm) of a comparative particle trap and a particle trap according to an embodiment of the present invention.

[0023] Figure 5 The particle collection efficiency (PN-10nm) of a comparative particle trap and a particle trap according to an embodiment of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. These specific embodiments are further elaborations on the present invention and do not limit the present invention in any way.

[0025] See Figure 1 A catalytic converter for gasoline engines and its preparation method are disclosed. The catalytic converter includes: a particulate filter carrier and a coating applied to the carrier; the coating consists of a first coating and a second coating, wherein the first coating contains a carrier material and an active precious metal, and the coating is distributed along the inner wall of the particulate filter; the second coating is continuously distributed along the surface of the intake channel filter wall to effectively fill the openings in the intake channel wall.

[0026] The principle of this invention is:

[0027] To achieve gaseous pollutant purification and effectively reduce the impact of the catalytic coating on back pressure, the first coating exhibits an internal microporous distribution. While the large openings on the surface of the GPF support or its catalyst's inlet channel facilitate airflow and improve back pressure, they also cause particulate matter to overflow, resulting in low particulate matter capture efficiency. This invention employs a porous second coating, effectively filling the surface openings. Simultaneously, the material's hydrophobic and low bulk density properties prevent secondary openings caused by coating material shrinkage during drying or at high temperatures, thus avoiding particulate matter overflow. Combined with the synergistic effect of the first and second layers, multiple interceptions of particulate matter are achieved, thereby improving the initial capture efficiency for particles larger than 10 nm.

[0028] The particle traps used in the following examples all have the following specifications: Φ132.1*127 (mm), pore size of 300 cpsi, wall thickness of 8 mil, average pore diameter of 19.8 μm, D10 of 12.3 μm, and porosity of 68%.

[0029] Example 1 - Comparison

[0030] The catalytic filter trap is prepared as follows:

[0031] (1) Preparation of coating slurry: 510g of cerium-zirconium composite material (cerium content 30%), 175g of lanthanum-modified alumina and 65g of barium hydroxide octahydrate were added to deionized water in sequence and stirred to obtain a suspension. The slurry was then ground until the particle size D90 was 2.3μm; the precious metal content was 5g / ft. 3 @0:3:2 (platinum:palladium:rhodium) Rhodium and palladium were loaded sequentially, with rhodium and palladium added in the form of nitrates; aluminum glue was used to adjust the slurry viscosity to 650 cps and the solid content to 27%;

[0032] (2) Using a vacuum suction coating method, the above coating slurry was applied from the inlet and outlet of the particle collector with a load of 100g / L and a 1:1 partition coating length. After drying, it was calcined at 550℃ for 2h.

[0033] Example 2

[0034] The catalytic filter trap is prepared as follows:

[0035] (1) First coating: 612.7g of cerium-zirconium composite material (cerium content 30%), 142.6g of lanthanum-modified alumina and 38.1g of barium acetate were added to a certain amount of deionized water in sequence, stirred to obtain a suspension, and ground until the slurry particle size D90 was 2.3μm; according to the precious metal content of 5g / ft 3 A 0:3:2 (platinum:palladium:rhodium) mixture was sequentially loaded with rhodium and palladium, which were added in the form of nitrates. Aluminum glue was used to adjust the slurry, achieving a viscosity of 900 cps and a solid content of 20.3%. Vacuum suction coating was used, with a loading rate of 50 g / L and a 1:1 coating length, to coat the slurry from both the inlet and outlet of the particulate filter. The resulting particulate filter catalyst with the first coating was obtained after drying at 120°C.

[0036] (2) Second coating: 42.63g of lanthanum-modified alumina was added to a certain amount of deionized water. After stirring, methyl hydroxyethyl cellulose was added to adjust the slurry viscosity to 350cps and control the solid content to 3.8%. Vacuum suction coating was used to coat the slurry from the inlet end of the particle trap that had been coated with the first coating at a loading rate of 9g / L. The coating height was 120mm. After drying at 120℃, it was calcined at 550℃ for 2h to obtain a catalyst with particles distributed along the wall of the inlet channel. The lanthanum-modified alumina used had a D90 of 24.3μm and a bulk density of 0.18g / cm³. 3 Specific surface area is 200m² 2 / g, pore volume 0.68cm 3 / g.

[0037] Example 3

[0038] The catalytic filter trap is prepared as follows:

[0039] (1) The catalyst obtained according to Example 2 is the first coating of this example;

[0040] (2) Second coating: 42.63g of lanthanum modified alumina was added to a certain amount of deionized water and stirred. Then, methyl hydroxyethyl cellulose was added to adjust the slurry viscosity to 400cps and control the solid content to 4.9%. The slurry was coated from the inlet end of the particle trap with the first coating at a loading of 12g / L using a vacuum suction coating method. The coating height was 123mm. After drying at 120℃, it was calcined at 550℃ for 2h to obtain a catalyst with particles distributed along the wall of the inlet channel. The second coating material used was the same as that used in the second coating in Example 2.

[0041] Example 4

[0042] The catalytic filter trap is prepared as follows:

[0043] (1) The catalyst obtained according to Example 2 is the first coating of this example;

[0044] (2) Second coating: 42.63g of lanthanum modified alumina was added to a certain amount of deionized water and stirred. Then, methyl hydroxyethyl cellulose was added to adjust the slurry viscosity to 500cps and control the solid content to 6.2%. The slurry was coated from the inlet end of the particle trap with the first coating at a loading of 15g / L using a vacuum suction coating method. The coating height was 119mm. After drying at 120℃, it was calcined at 550℃ for 2h to obtain a catalyst with particles distributed along the wall of the inlet channel. The second coating material used was the same as that used in the second coating in Example 2.

[0045] Example 5

[0046] The catalytic converter for gasoline engines according to Example 4 was obtained by calcining at 1000°C for 10 hours.

[0047] Example 6

[0048] The catalytic filter trap is prepared as follows:

[0049] (1) First coating: 334.2g of cerium-zirconium composite material (cerium content 40%), 77.8g of lanthanum-modified alumina and 20.8g of barium acetate were added to a certain amount of deionized water in sequence, stirred to obtain a suspension, and ground until the slurry particle size D90 was 1.3μm; according to the precious metal content of 10g / ft 3 Rhodium and palladium were sequentially loaded in a 0:7:3 (platinum:palladium:rhodium) mixture, with rhodium and palladium added in the form of nitrates. The slurry viscosity was adjusted to 620 cps using methyl hydroxyethyl cellulose, and the solid content was 22.7%. A vacuum suction coating method was used, with a loading of 80 g / L and a 1:1 coating ratio, applied to the particulate filter from both the inlet and outlet ends. The resulting particulate filter catalyst with the first coating was obtained after drying at 120°C.

[0050] (2) Second coating: 15.032 g of lanthanum-modified alumina A and 22.55 g of lanthanum-modified alumina were added to deionized water. After stirring, methyl hydroxyethyl cellulose was added to adjust the slurry viscosity to 560 cps and control the solid content to 4.8%. Vacuum suction coating was used to coat the slurry from the inlet end of the particle trap that had been coated with the first coating at a loading rate of 12 g / L. The coating height was 119 mm. After drying at 120 °C, the slurry was calcined at 550 °C for 2 h to obtain a catalyst with particles distributed along the wall of the inlet channel. The lanthanum-modified alumina A used had a D90 of 5.8 μm and a bulk density of 0.16 g / cm³. 3 Specific surface area is 250m² 2 / g, pore volume 0.86cm 3 / g; Lanthanum-modified alumina B: D90 is 26.1μm, bulk density is 0.14g / cm³ 3 Specific surface area is 291m² 2 / g, pore volume 0.61cm 3 / g

[0051] Example 7

[0052] The catalytic filter trap is prepared as follows:

[0053] (1) First coating: 278.5g of cerium-zirconium composite material (cerium content 30%), 64.8g of lanthanum-modified alumina and 17.3g of barium acetate were added to a certain amount of deionized water in sequence, stirred to obtain a suspension, and ground until the slurry particle size D90 was 2.5μm; according to the precious metal content of 3g / ft 3 A 0:2:1 (platinum:palladium:rhodium) mixture was sequentially loaded with rhodium and palladium, which were added in the form of nitrates. The slurry was adjusted with methyl hydroxyethyl cellulose to a viscosity of 850 cps and a solid content of 32%. The slurry was applied from the inlet of the particulate filter using a vacuum suction coating method at a loading rate of 70 g / L. The coating height was 110 mm, and the catalyst was dried at 120°C to obtain the particulate filter catalyst with the first coating.

[0054] (2) Second coating:

[0055] 62.64g of lanthanum-modified alumina was added to a certain amount of deionized water and stirred. Then, methyl hydroxyethyl cellulose was added to adjust the slurry viscosity to 460cps and control the solid content to 7.1%. The slurry was coated from the inlet end of the particle trap with the first coating at a loading of 18g / L using a vacuum suction coating method. The coating height was 123mm. After drying at 120℃, it was calcined at 550℃ for 2h to obtain a catalyst with particles distributed along the wall of the inlet channel. The second coating material used was the same as that used in the second coating in Example 2.

[0056] Example 8

[0057] The catalytic filter trap is prepared as follows:

[0058] (1) First coating: 305.2g of cerium-zirconium composite material (cerium content 40%), 104.9g of lanthanum-modified alumina, and 39.1g of barium hydroxide octahydrate were added to deionized water in sequence, stirred to obtain a suspension, and ground until the slurry particle size D90 was 1.8μm; according to the precious metal content of 3g / ft 3Rhodium and palladium were sequentially loaded in a 0:2:1 (platinum:palladium:rhodium) mixture, with rhodium and palladium added in the form of nitrates. The viscosity of the slurry was adjusted to 505 cps using methyl hydroxyethyl cellulose, and the solid content was 23.3%. Vacuum suction coating was used, with the above coating slurry applied to the inlet and outlet of the particulate filter in sections with a loading of 70 g / L and a coating length of 1:1. After drying at 120°C, the particulate filter catalyst with the first coating was obtained.

[0059] (2) Second coating: 62.6g of cerium-zirconium-aluminum composite (cerium content 12.5%, aluminum content 50%) was added to a certain amount of deionized water. After stirring, methyl hydroxyethyl cellulose was added to adjust the slurry viscosity to 350cps and control the solid content to 7.7%. Vacuum suction coating was used to coat the slurry from the inlet end of the particle trap that had been coated with the first coating at a loading rate of 20g / L, with a coating height of 120mm. After drying at 120℃, it was calcined at 550℃ for 2h to obtain a catalyst with particles distributed along the wall of the inlet channel. The cerium-zirconium-aluminum composite used had a D90 of 16.3μm and a bulk density of 0.80g / cm³. 3 Specific surface area is 85m² 2 / g, pore volume 0.56cm 3 / g.

[0060] Example 9

[0061] The catalytic filter trap is prepared as follows:

[0062] (1) First coating: 334.2g of cerium-zirconium composite material (cerium content 35%), 77.8g of lanthanum-modified alumina and 20.8g of barium acetate were added to a certain amount of deionized water in sequence, stirred to obtain a suspension, and ground until the slurry particle size D90 was 1.5μm; according to the precious metal content of 5g / ft 3 Rhodium and platinum were sequentially loaded in a 4:0:1 (platinum:palladium:rhodium) mixture, with rhodium and platinum added in the form of nitrates. The viscosity of the slurry was adjusted to 550 cps using methyl hydroxyethyl cellulose, and the solid content was 24.1%. The slurry was coated using a vacuum suction coating method, with a coating load of 80 g / L and a coating height of 1:1 in sections. The coating slurry was applied from the inlet and outlet of the particulate filter. After drying at 120°C, it was calcined at 550°C for 2 hours to obtain the particulate filter catalyst with the first coating.

[0063] (2) Second coating: with a thickness of 292m 2 High-specific-surface-area boehmite is loaded into a particle-aerosol using a loading device, and then loaded onto the catalyst inlet end face to obtain a catalyst with a coating distributed along the inlet channel wall. The boehmite used has a D90 of 21.4 μm, a bulk density of 0.16 g / ml, and a pore volume of 1.0 cm³. 3 / g; outer layer loading is 7g / L;

[0064] Example 10

[0065] According to the catalytic converter for gasoline engines in Example 8, the second coating loading is 5 g / L, the lanthanum-modified alumina used has a D90 of 40.3 μm, and a bulk density of 0.28 g / cm³. 3 Specific surface area 183m 2 / g, pore volume 0.83cm 3 / g;

[0066] Example 11 - Back pressure and capture efficiency test

[0067] (I) Back pressure test

[0068] The catalytic converter for gasoline engines obtained in the examples was subjected to back pressure tests at room temperature (25±5℃) and cold flow (600CMH) using a superflow apparatus. The results are as follows: Figure 3 As shown, compared to the prior art catalytic converter for gasoline engines (Example 1), the back pressure of the particulate filter of the present invention is slightly increased; under the same first coating conditions, the back pressure of the particulate filter increases with the increase of the amount of the second coating; the back pressure of the particulate filter is affected by both the first coating and the second coating.

[0069] (II) Capture Efficiency Test

[0070] The catalytic converter-type gasoline engine particulate filter (CGPF) obtained in the examples was tested on a China VI 1.5T GDI vehicle according to GB18352.6-2016 "Limits and Measurement Methods for Pollutant Emissions from Light-Duty Vehicles (China VI)" standard. The vehicle's aftertreatment system consisted of a tightly coupled three-way catalyst (TWC) and CGPF. The CGPF used in the tests was either fresh or at zero kilometers. Particulate matter (23nm, 10nm) was collected from the original exhaust and the corresponding particulate matter tailpipe after the CGPF. The capture efficiency results for particulate matter (23nm, 10nm) are as follows: Figure 4 , Figure 5 As shown.

[0071] from Figure 4 , Figure 5It can be seen that, compared with Example 1 used for comparison, Examples 2-10 of the present invention have a 20-30% improvement in the capture efficiency of 23nm and 10nm particles. The improvement in capture efficiency is due to the filling of the openings on the wall surface by the distribution of the second coating and the synergy between the first and second coatings. As can be seen from Examples 2-4, the particle capture efficiency of the trap increases with the increase of the second coating load. Among them, Example 4 has a capture efficiency of 97% for particles larger than 10nm, and its capture efficiency remains at a considerable level after aging at 1000℃ (Example 5). As can be seen from the examples, compared with 23nm particles, its capture efficiency for particles larger than 10nm is 1-3% higher. By adjusting the first and second coatings, a high initial capture efficiency for particles larger than 10nm can be achieved.

Claims

1. A method for preparing a catalytic converter for gasoline engines, the converter comprising a particulate filter carrier and a coating applied to the carrier; the coating comprises a first coating and a second coating, the first coating comprising a carrier material and an active noble metal, and the second coating comprising one or more of boehmite, alumina, lanthanum-modified alumina, silicon-modified alumina, calcium carbonate, and cerium-zirconium-aluminum composite. The first coating is distributed along the inner wall of the particulate filter carrier, and the second coating is continuously distributed along the surface of the filter wall of the air intake channel. The active noble metal in the first coating is one or more of platinum, palladium, and rhodium; The bulk density of the second coating material is 0.1~1 g / cm³. 3 Its BET specific surface area is 10~300m² 2 / g, with a pore volume of 0.5~1.2cm. 3 / g; The second coating has loose, porous, and hydrophobic properties; The length of the second coating is 90-100% of the length of the particulate trap; Its features are, Includes the following steps: (1) Preparation of the first coating Cerium-zirconium composite material, alumina and alkaline earth metal compound were added to deionized water and stirred to obtain a suspension slurry. After grinding, the slurry is loaded with precious metals to obtain a precious metal-loaded slurry. The viscosity of the slurry loaded with precious metals is adjusted by using a viscosity modifier, and the solid content of the slurry is controlled to be 15-35%. The slurry is then coated onto the particle collector carrier using a vacuum suction coating method. The particulate filter catalyst coated with the first coating layer is obtained by drying at 100~120℃; (2) Preparation of the second coating The second coating material is added to deionized water, stirred, and then a viscosity modifier is added to control the solid content of the slurry to 3-20% to obtain the second coating slurry. The second coating slurry is applied along the air inlet of the particle trap that has already been coated with the first coating using a vacuum suction coating method. After drying at 100~130℃, the mixture is calcined at 500~600℃ for 1~4h at a heating rate of 2~5℃ / min to obtain a catalytic gasoline engine particulate filter.

2. The method for preparing a catalytic converter for gasoline engines according to claim 1, characterized in that, The particle size D90 of the slurry in the first coating is smaller than the particle size D10 of the particle trap carrier; the loading of the first coating is 30~120g / L.

3. The method for preparing a catalytic converter for gasoline engines according to claim 1, characterized in that, The loading of the second coating is 3~30g / L.

4. A method for preparing a catalytic converter for gasoline engines according to any one of claims 1-3, characterized in that, The viscosity modifier used in the preparation of the first coating and the second coating is one or more of methyl hydroxyethyl cellulose, aluminum glue, polyethylene glycol, and guar gum.

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