Catalytic wall flow filter

Abstract

A catalytic wall-flow filter for exhaust gases from a gasoline engine is disclosed. The catalytic wall-flow filter comprises a wall-flow filter substrate, a first TWC coating in a first plurality of channels, and a second TWC coating in a second plurality of channels. The first TWC coating comprises palladium, rhodium, a first oxygen storage capacity (OSC) material, and a first inorganic support. The second TWC coating comprises platinum, rhodium, a second OSC material, and a second inorganic support.

Description

[Technical Field]

[0001] The present invention relates to a catalytic wall flow filter suitable for use in vehicle exhaust treatment systems, particularly in exhaust treatment systems for positive ignition internal combustion engines such as gasoline spark-ignition engines. This catalytic wall flow filter is effective in reducing emissions of HC, CO, NOx, and particulate matter. [Background technology]

[0002] A gasoline particulate filter (GPF) is an after-treatment technology developed to control particulate emissions from gasoline direct injection (GDI) engines.

[0003] The number of GDI vehicles is increasing, driven by demands for CO2 reduction and / or fuel economy. In 2016, an estimated 60% of new gasoline cars in Europe were GDI. The proportion of GDI vehicles is also increasing rapidly in North America, and within nine years of its first significant market use, GDI penetration has risen to 48.5% of new light vehicle sales in the United States. Emissions from the growing fleet of GDI vehicles are a public health concern and a potential major source of ambient particulate pollution in densely populated urban areas.

[0004] Most early GPF applications involved uncoated GPF positioned downstream of a three-way catalyst (TWC). As the technology matured, GPF also began to be coated with the three-way catalyst. This catalyst-coated GPF configuration is sometimes referred to as a four-way catalyst. See, for example, U.S. Patent No. 10,625,243(B2), U.S. Patent Application No. 2020 / 0353410(A1), U.S. Patent Application No. 2019 / 0168162(A1), and U.S. Patent Application No. 2009 / 0193796(A1). However, the combination of TWC coating on the filter body introduces additional problems such as excessive back pressure, and there are requirements for minimal CO, NOx, and HC conversion characteristics. In addition, cost is a consideration, as it must provide the best possible balance between performance and cost.

[0005] A three-way catalytic converter is intended to catalyze three simultaneous reactions: (i) the oxidation of carbon monoxide to carbon dioxide, (ii) the oxidation of unburned hydrocarbons to carbon dioxide and water, and (iii) the reduction of nitrogen oxides to nitrogen and oxygen. These three reactions occur most efficiently when the TWC receives exhaust gas from an engine operating at or near its stoichiometric point. As is well known in the art, the amount of carbon monoxide, unburned hydrocarbons, and nitrogen oxides emitted when gasoline fuel is burned in an externally ignited (e.g., spark-ignition) internal combustion engine is mainly influenced by the air-fuel ratio in the combustion chamber. Exhaust gas with a stoichiometrically balanced composition is less likely to produce oxidizing gases (NOx). x The concentrations of oxygen (O2) and reducing gases (HC and CO) are substantially equal. The air-fuel ratio that produces this stoichiometrically balanced exhaust gas composition is typically 14.7:1.

[0006] Typical active ingredients in TWC include platinum and / or palladium combined with rhodium supported on a high-surface-area oxide, as well as oxygen storage capacity (OSC) materials.

[0007] Theoretically, in an exhaust gas composition that is stoichiometrically balanced, O2, NO x It should be possible to completely convert CO, HC, and CO2, H2O, and N2 (and residual O2), and this is the role of the TWC. Therefore, ideally, the engine needs to be operated in such a way that the air-fuel ratio of the combustion mixture produces a stoichiometrically balanced exhaust gas composition.

[0008] The method for defining the compositional balance between oxidizing and reducing gases in exhaust gas is the lambda (λ) value of the exhaust gas, which can be defined according to the following formula. Lambda (λ) = (Actual engine air-fuel ratio) / (Stoichiometric air-fuel ratio) A lambda value of 1 represents a stoichiometrically balanced (or stoichiometric) exhaust gas composition; a lambda value greater than 1 represents excess O2 and NOx, and the composition is described as "lean"; and a lambda value less than 1 represents excess HC and CO, and the composition is described as "rich." It is also common in the art to refer to the air-fuel ratio in which an engine operates as "stoichiometric," "lean," or "rich," depending on the exhaust gas composition that the air-fuel ratio produces.

[0009] TWC used NO xIt should be understood that the reduction of CO to N2 becomes less efficient when the exhaust gas composition is lean or stoichiometric. Similarly, the TWC's ability to oxidize CO and HC is reduced when the exhaust gas composition is rich. Therefore, the challenge is to maintain the composition of the exhaust gas flowing into the TWC as close to a stoichiometric composition as possible. Naturally, when the engine is in a steady state, it is relatively easy to ensure that the air-fuel ratio is stoichiometric. However, when the engine is used to propel the vehicle, the amount of fuel required changes temporarily depending on the load demands placed on the engine by the driver. This makes it particularly difficult to control the air-fuel ratio so that a stoichiometric exhaust gas is produced for ternary conversion. In practice, the air-fuel ratio is controlled by an engine control unit, a so-called closed-loop feedback system, which receives information on the exhaust gas composition from an exhaust gas oxygen (EGO) (or lambda) sensor. A characteristic of such systems is that, due to the time lag associated with adjusting the air-fuel ratio, the air-fuel ratio oscillates (or perturbs) between a slightly rich stoichiometric (or control set) point and a slightly lean point. This perturbation is characterized by the amplitude of the air-fuel ratio fluctuation and the response frequency (Hz).

[0010] When the exhaust gas composition is slightly richer than the setpoint, a small amount of oxygen is required to consume unreacted CO and HC, i.e., to make the reaction more stoichiometric. Conversely, when the exhaust gas is slightly lean, excess oxygen needs to be consumed. This has been achieved by developing OSC materials that release or absorb oxygen during perturbation. OSC materials commonly used in modern TWCs are cerium oxide, or cerium-containing mixed oxides, such as CeZr mixed oxides.

[0011] There is a need to develop technologies to cost-effectively convert CO, NOx, and HC in exhaust gases from gasoline engines and reduce particulate matter. [Overview of the project]

[0012] One aspect of the present disclosure is a catalytic wall flow filter for exhaust gases from a gasoline engine, A wall flow filter substrate having a porous wall and a first surface and a second surface defining a longitudinal direction between them, and a plurality of first channels and a plurality of second channels extending in the longitudinal direction, wherein the plurality of first channels are open on the first surface and closed on the second surface, and the plurality of second channels are open on the second surface and closed on the first surface, A first TWC coating in a first plurality of channels, comprising palladium, rhodium, a first oxygen storage capacity (OSC) material, and a first inorganic support, A second TWC coating in a second plurality of channels, comprising platinum, rhodium, a second OSC material, and a second inorganic support, Equipped with, The first TWC coating is applied from the first surface. The second TWC coating is applied from the second surface. This invention relates to a catalytic wall flow filter, wherein the first surface is the inlet surface of the catalytic wall flow filter, and the second surface is the outlet surface of the catalytic wall flow filter.

[0013] Another aspect of this disclosure is a method for manufacturing a catalytic wall flow filter for exhaust gas treatment, (i) Forming a first wash coat slurry comprising palladium, rhodium, a first oxygen storage capacity (OSC) material, and a first inorganic support, (ii) Coating the wall flow filter substrate with a first wash coat slurry, wherein the wall flow filter substrate has a porous wall and has a first surface and a second surface that define a longitudinal direction therebetween, and a first plurality of channels and a second plurality of channels that extend in the longitudinal direction, the first plurality of channels being open at the first surface and closed at the second surface, the second plurality of channels being open at the second surface and closed at the first surface, and the first wash coat slurry being coated from the first surface. (iii) Forming a second wash coat slurry comprising platinum, rhodium, a second oxygen storage capacity (OSC) material, and a second inorganic carrier. (iv) Coating the wall flow filter substrate with the second wash coat slurry from the second surface of the wall flow filter substrate to form a wash-coated wall flow filter substrate. (v) Calcining the wash-coated wall flow filter substrate to form a catalytic wall flow filter. Relates to a method comprising the above.

[0014] Another aspect of the present disclosure is an exhaust treatment system for treating the flow of combustion exhaust gas from a gasoline direct injection engine, the system comprising the catalytic wall flow filter disclosed herein. Preferably, the exhaust system comprises a TWC catalyst and a catalytic wall flow filter, and the TWC catalyst is upstream of the catalytic wall flow filter.

[0015] According to a further aspect, the present invention provides a method for treating combustion exhaust gas from an external combustion engine containing nitrogen oxides, carbon monoxide, hydrocarbons, and particulate matter, the method comprising contacting the exhaust gas with the catalytic wall flow filter disclosed herein.

Brief Description of the Drawings

[0016] [Figure 1] Shows the CO conversion rates of GPF-1 to GPF-5. [Figure 2] It shows the total hydrocarbon conversion rates of GPF-1 to GPF-5. [Figure 3] It shows the NOx conversion rates of GPF-1 to GPF-5.

Embodiments for Carrying out the Invention

[0017] Here, the present disclosure will be further described. In the following sections, different aspects / embodiments of the present disclosure will be defined in more detail. Each aspect / embodiment so defined may be combined with any other aspect / embodiment or multiple aspects / multiple embodiments unless otherwise explicitly indicated. In particular, any feature shown as being preferred or advantageous may be combined with any other feature or multiple features shown as being preferred or advantageous.

[0018] One aspect of the present disclosure is a catalytic wall flow filter for exhaust gas from a gasoline engine, comprising

[0019] a wall flow filter substrate having a porous wall and having a first surface and a second surface that define a longitudinal direction therebetween, and a first plurality of channels and a second plurality of channels extending in the longitudinal direction, wherein the first plurality of channels are open at the first surface and closed at the second surface, and the second plurality of channels are open at the second surface and closed at the first surface, a first TWC coating within the first plurality of channels, the first TWC coating comprising palladium, rhodium, a first oxygen storage capacity (OSC) material, and a first inorganic carrier, a second TWC coating within the second plurality of channels, the second TWC coating comprising platinum, rhodium, a second OSC material, and a second inorganic carrier, and the first TWC coating is coated from the first surface, the second TWC coating is coated from the second surface, This invention relates to a catalytic wall flow filter, wherein the first surface is the inlet surface of the catalytic wall flow filter, and the second surface is the outlet surface of the catalytic wall flow filter.

[0020] The wall flow filter substrate may be a ceramic, for example, a composite material containing silicon carbide, cordierite, aluminum nitride, silicon nitride, aluminum titanate, alumina, mullite, pollucite, or any two or more segments thereof. Cordierite, magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0021] Suitable wall-flow filter substrates for use in the present invention typically have an average pore size of 8 to 45 μm, for example, 8 to 25 μm, or 10 to 20 μm. Pore sizes are well known to those skilled in the art, and appropriate measurement techniques are known to those skilled in the art. Wall-flow filter substrates may have a porosity of 40 to 75%, for example, 45 to 70%. The average pore size may be determined using mercury porosimetry and X-ray tomography according to conventional methods.

[0022] The catalytic wall flow filter includes a first TWC coating in a first plurality of channels. The first TWC coating preferably contains palladium and rhodium in a weight ratio of 10:1 to 1:10, more preferably 5:1 to 1:5, and most preferably 2:1 to 1:2. The first TWC coating may further contain platinum. In some embodiments, the amount of the first TWC coating supported includes a barium component.

[0023] The catalytic wall flow filter includes a second TWC coating in a second plurality of channels. The second TWC coating preferably contains platinum and rhodium in a weight ratio of 10:1 to 1:10, more preferably 5:1 to 1:5, and most preferably 2:1 to 1:2. The second TWC coating may further contain palladium.

[0024] "Oxygen storage capacity" refers to the ability of a material used as an oxygen storage material in a catalyst composition to absorb oxygen under lean conditions and release oxygen under rich conditions.

[0025] The first OSC material and the second OSC material may be the same or different. The first OSC material and the second OSC material may each be ceria or a mixed oxide containing ceria. Preferably, the first OSC material and the second OSC material may each contain a mixed oxide of cerium and zirconium; a mixed oxide of cerium, zirconium, and aluminum; a mixed oxide of cerium, zirconium, and neodymium; or a mixed oxide of cerium, zirconium, and praseodymium. When used herein, the term "mixed oxide" generally refers to a mixture of oxides in a single phase, as is conventionally known in the art.

[0026] The amount of OSC material in the first TWC coating or the second TWC coating may be 5 to 90% by weight, preferably 10 to 80% by weight, relative to the total weight of the coating.

[0027] In some embodiments, each of the first OSC material and the second OSC material independently comprises OSCs derived from a CeZr mixed oxide sol having a D90 of less than 1.3 microns. The CeZr mixed oxide sol comprises CeZr mixed oxide (CeZr mixed oxide particles or CeZr mixed oxide nanoparticles) dispersed in an aqueous medium.

[0028] The particle size distribution can be characterized by the D10, D50, and D90 measurements. In each case, the numerical value indicates the proportion of particles smaller than the stated value. In other words, a D90 of 100 microns means that 90% of the particles are smaller than 100 microns in diameter. Knowing D10 and D90 allows us to define the range of particles in the particle distribution. The characteristics of the particle size of a sample by the D10 and D90 values ​​generally define the width of the particle size distribution. The closer these values ​​are, the narrower the particle size distribution.

[0029] The particle size measurements required to obtain the D10, D50, and D90 values ​​of CeZr mixed oxide sols and / or particulate inorganic oxides can be obtained by laser diffraction particle size analysis using the Malvern Mastersizer 3000, which is a volume-based method (i.e., D50 and D90 are D V 50 and D V The particle size distribution is determined by applying a mathematical Mie theory model to 90 (or possibly D(v,0.50) and D(v,0.90)). The laser diffraction system works by determining the particle diameter based on the spherical approximation. For particle size measurement by laser diffraction particle size analysis, diluted samples were prepared by sonication in surfactant-free distilled water at 35 watts for 30 seconds.

[0030] In some embodiments, the D90 of the CeZr mixed oxide sol may be less than 1.2 microns, or less than 1.1 microns, or less than 1.0 micron, or less than 900 nm, or less than 800 nm, or less than 700 nm, or less than 600 nm, or less than 500 nm, or less than 400 nm, or less than 300 nm.

[0031] In some other embodiments, the D90 of the CeZr mixed oxide sol may be 1.2 to 1.3 microns, or 1.1 to 1.2 microns, or 1.0 to 1.1 microns, or 900 nm to 1.0 micron, or 800 nm to 900 nm, or 700 nm to 800 nm, or 600 nm to 700 nm, or 500 nm to 600 nm, or 400 nm to 500 nm, or 300 nm to 400 nm, or 200 nm to 300 nm, or 100 nm to 200 nm.

[0032] The CeZr mixed oxide sol may have a D50 of 100 nm to 700 nm, preferably 200 nm to 600 nm, and more preferably 300 nm to 400 nm.

[0033] Particle size can also be characterized by obtaining the Z-mean particle size of the sample. The Z-mean is the intensity-weighted average hydrodynamic size of an ensemble collection of particles measured by dynamic light scattering (DLS). The Z-mean is derived from the cumulant analysis of the measured correlation curve, assuming a single particle size, and a single exponential fit is applied to the autocorrelation function. The particle size measurements required to obtain the Z-mean particle size of a CeZr mixed oxide sol can be obtained by dynamic light scattering particle size analysis using a Malvern Zetasizer Nano. All tests are performed in a diluted aqueous medium, and the harmonic mean hydrodynamic diameter of the sphere of equivalent diffusivity is determined by the time-dependent cumulant analysis of light scattered by randomly moving particles according to the Stokes-Einstein equation.

[0034] The Z-average particle size of the CeZr mixed oxide sol is preferably 150 nm to 350 nm, more preferably 230 nm to 310 nm.

[0035] The first inorganic oxide support and the second inorganic oxide support may each be an oxide of an element from Group 2, Group 3, Group 4, Group 5, Group 13, and Group 14. The inorganic oxide support is preferably a refractory oxide that exhibits chemical and physical stability at high temperatures, such as those associated with gasoline engine emissions. The first inorganic oxide support and the second inorganic oxide support may each be selected from the group consisting of alumina, silica, titania, and mixed oxides or composite oxides thereof. More preferably, the inorganic oxide support is alumina.

[0036] Inorganic oxide supports such as alumina can be doped with dopants. Dopants can be selected from the group consisting of La, Sr, Si, Ba, Y, Pr, Nd, Ce, and mixtures thereof. Preferably, the dopant is La, Ba, or Ce. Most preferably, the dopant is La. The dopant content in the inorganic oxide support may be 1 to 30% by weight, preferably 2 to 25% by weight, and more preferably 3 to 20% by weight.

[0037] The D50 of the first or second inorganic material may be in the range of 0.1 to 100 μm, preferably in the range of 0.1 to 50 μm.

[0038] In some embodiments, the first inorganic oxide support is alumina doped with 2 to 25% by weight, more preferably 3 to 20% by weight of La.

[0039] In some embodiments, the second inorganic oxide support is alumina doped with 2 to 25% by weight, more preferably 3 to 20% by weight of La.

[0040] The OSC material and inorganic oxide support in the first or second TWC coating may have a weight ratio of 10:1 to 1:10, preferably 5:1 to 1:5, and more preferably 3:1 to 1:3.

[0041] The first TWC coating preferably covers 30% to 80%, more preferably 50% to 55%, of the length of the first plurality of channels.

[0042] The second TWC coating preferably covers 30% to 80%, more preferably 50% to 55%, of the length of the second plurality of channels.

[0043] The first TWC coating and the second TWC coating may each be an in-wall coating, an on-wall coating, or a combination of an in-wall coating and an on-wall coating.

[0044] The loading amount of the first TWC coating is 0.3-1.5 g / in. 3 Preferably 0.5 to 1.0 g / in 3 It may be within the range. The amount of the first TWC coating supported is defined as the weight of the first TWC coating relative to the total volume of the catalyst wall flow filter after calcination.

[0045] The supported amount of the second TWC coating is 0.3 to 1.5 g / in 3 , preferably 0.5 to 1.0 g / in 3 and can be within the range of.

[0046] The first TWC coating may have a PGM supported amount in the range of 2 to 10 g / ft 3 , preferably 3 to 9 g / ft 3 , more preferably 4 to 8 g / ft 3 and may have a PGM supported amount in the range of.

[0047] PGM refers to platinum group metals and includes platinum, palladium, rhodium, ruthenium, iridium, and osmium.

[0048] The second TWC coating may have a PGM supported amount in the range of 2 to 10 g / ft 3 , preferably 3 to 9 g / ft 3 , more preferably 4 to 8 g / ft 3 and may have a PGM supported amount in the range of.

[0049] Preferably, the weight ratio of palladium to platinum in the catalytic wall flow filter is in the range of 10:1 to 1:10, more preferably 5:1 to 1:5, and even more preferably 2:1 to 1:2. In one embodiment, the weight ratio of palladium to platinum in the catalytic wall flow filter is about 1:1.

[0050] The PGM supported amount of the first TWC coating is defined as the weight of the total PGM in the first TWC coating relative to the total volume of the calcined catalytic wall flow filter. Similarly, the PGM supported amount of the second TWC coating is defined as the weight of the total PGM in the second TWC coating relative to the total volume of the calcined catalytic wall flow filter.

[0051] Another aspect of the present disclosure is a method for manufacturing a catalytic wall flow filter for exhaust gas treatment, comprising (i) Forming a first wash coat slurry comprising palladium, rhodium, a first oxygen storage capacity (OSC) material, and a first inorganic support, (ii) Coating a wall flow filter substrate with a first wash coat slurry, wherein the wall flow filter substrate has a porous wall having a first surface and a second surface defining the longitudinal direction between them, and a first plurality of channels and a second plurality of channels extending in the longitudinal direction, wherein the first plurality of channels are open on the first surface and closed on the second surface, and the second plurality of channels are open on the second surface and closed on the first surface, and the first wash coat slurry is coated from the first surface. (iii) Forming a second washcoat slurry comprising platinum, rhodium, a second oxygen storage capacity (OSC) material, and a second inorganic support, (iv) Coating the wall flow filter substrate with a second wash coat slurry from the second surface of the wall flow filter substrate to form a washed wall flow filter substrate, (v) Forming a catalytic wall flow filter by calcining a wash-coated wall flow filter substrate, Regarding methods, including those mentioned above.

[0052] The first washcoat slurry and the second washcoat slurry generally contain a solvent. Water and organic solvents (such as methanol, ethanol, or propanol) or mixtures thereof can be used. Preferably, water is used as the solvent.

[0053] Typically, the first washcoat slurry and / or the second washcoat slurry have a solids content of 20-30% by weight.

[0054] The first wash coat slurry may further contain a barium component.

[0055] The method includes coating a wall flow filter substrate with a first wash coat slurry from a first surface, and coating the wall flow filter substrate with a second wash coat slurry from a second surface to form a washed-coated wall flow filter substrate. One preferred coating procedure is described in U.S. Patent No. 6,599,570 (B1). The second wash coat slurry may be applied before the first wash coat slurry, or vice versa.

[0056] After applying one or both of the first wash coat slurry and the second wash coat slurry to the wall flow filter substrate, it may be preferable to dry the wall flow filter substrate containing one of the coatings at a certain temperature (e.g., 100-200°C) before applying another coating.

[0057] Caulking is commonplace in the art and can be carried out under normal conditions, for example, at about 500°C.

[0058] Another aspect of the present disclosure is an exhaust treatment system for treating the flow of combustion exhaust gases from a gasoline direct injection engine, the system comprising a catalytic wall flow filter disclosed herein. The exhaust system may include additional components, such as a TWC catalyst comprising a TWC composition, which is applied to a honeycomb flow-through substrate and is positioned either upstream or downstream of the catalytic wall flow filter according to the present invention.

[0059] Preferably, the exhaust system includes a TWC catalyst and a catalytic wall flow filter as disclosed herein, wherein the TWC catalyst is located upstream of the catalytic wall flow filter.

[0060] This catalytic wall flow filter is effective in reducing emissions of hydrocarbons, CO, NOx, and particulate matter.

[0061] In a further embodiment, the present invention provides a method for treating combustion exhaust gases from an externally ignited internal combustion engine, comprising contacting the exhaust gases with a catalytic wall flow filter disclosed herein, wherein the exhaust gases contain nitrogen oxides, carbon monoxide, hydrocarbons, and particulate matter. [Examples]

[0062] Comparative Example 1: GPF-1 A washcoat slurry ("Slurry A") was prepared by mixing rhodium nitrate, palladium nitrate, a CeZr mixed oxide sol with a ZrO2 to CeO2 weight ratio of approximately 2:1 and a D90 of less than 1 μm, a La-stabilized alumina component with a D90 of 5 μm, barium hydroxide, and water. The solid content was approximately 24%.

[0063] Using the coating process described in U.S. Patent No. 6,599,570 (B2), a cordierite wall-flow filter substrate (4.66 × 4.5 inches, 300 / 8, average pore size 15 microns, porosity 65%) was coated with slurry A from the inlet and outlet faces. The length of both the inlet and outlet wash coatings was approximately 50–55% of the substrate length. After applying each coating, the coated filter substrate was dried at 115°C. The coated filter substrate was baked at 500°C for 1 hour. After baking, the coated filter (GPF-1) had a viscosity of 1.6 g / in 3 Wash coat load capacity and 8g / ft 3 It had a total PGM load, and the Pd:Rh weight ratio was 1:1.

[0064] Comparative Example 2: GPF-2 A washcoat slurry ("Slurry B") was prepared by mixing rhodium nitrate, palladium nitrate, platinum nitrate, a CeZr mixed oxide sol with a ZrO2 to CeO2 weight ratio of approximately 2:1 and a D90 of less than 1 μm, a La-stabilized alumina component with a D90 of 5 μm, barium hydroxide, and water. The solid content was approximately 24%.

[0065] Using the coating process described in U.S. Patent No. 6,599,570 (B2), a cordierite wall-flow filter substrate (4.66 × 4.5 inches, 300 / 8, average pore size 15 microns, porosity 65%) was coated with slurry B from the inlet and outlet ends. The length of both the inlet and outlet wash coatings was approximately 50–55% of the substrate length. After applying each coating, the coated filter substrate was dried at 115°C. The coated filter substrate was baked at 500°C for 1 hour. After baking, the coated filter (GPF-2) had a viscosity of 1.6 g / in 3 Wash coat load capacity and 8g / ft 3 It had a total PGM load, and the weight ratio of Pt:Pd:Rh was 1:1:2.

[0066] Comparative Example 3: GPF-3 A washcoat slurry ("Slurry C") was prepared by mixing rhodium nitrate, platinum nitrate, a CeZr mixed oxide sol with a weight ratio of ZrO2 to CeO2 of approximately 2:1 and a D90 of less than 1 μm, and a La-stabilized alumina component with a D90 of 5 μm. The solid content was approximately 24%.

[0067] Using the coating process described in U.S. Patent No. 6,599,570 (B2), a cordierite wall-flow filter substrate (4.66 × 4.5 inches, 300 / 8, average pore size 15 microns, porosity 65%) was coated with slurry C from the inlet and outlet surfaces. The length of both the inlet and outlet wash coatings was approximately 50–55% of the substrate length. After applying each coating, the coated filter substrate was dried at 115°C. The coated filter substrate was baked at 500°C for 1 hour. After baking, the coated filter (GPF-3) had a viscosity of 1.6 g / in 3 Wash coat load capacity and 8g / ft 3 It had a total PGM load, and the Pt:Rh weight ratio was 1:1.

[0068] Example 1: GPF-4 Using the coating process described in U.S. Patent No. 6,599,570 (B2), a cordierite wall flow filter substrate (4.66 × 4.5 inches, 300 / 8, average pore size 15 microns, porosity 65%) was coated with slurry A from the inlet side. The length of the inlet wash coating was approximately 50–55% of the substrate length. After drying at 115°C, the substrate was coated with slurry C from the outlet side. The length of the outlet wash coating was approximately 50–55% of the substrate length. The coated filter substrate was then dried at 115°C and baked at 500°C for 1 hour. After baking, the coated filter (GPF-4) had a viscosity of 1.6 g / in 3 Wash coat load capacity and 8g / ft 3 It had a total PGM load, and the weight ratio of Pt:Pd:Rh was 1:1:2.

[0069] Comparative Example 4: GPF-5 Using the coating process described in U.S. Patent No. 6,599,570 (B2), a cordierite wall-flow filter substrate (4.66 × 4.5 inches, 300 / 8, average pore size 15 microns, porosity 65%) was coated with slurry C from the inlet side. The length of the inlet wash coating was approximately 50–55% of the substrate length. After drying at 115°C, it was then coated with slurry A from the outlet side. The length of the outlet wash coating was approximately 50–55% of the substrate length. The coated filter substrate was then dried at 115°C and baked at 500°C for 1 hour. After baking, the coated filter (GPF-5) had a viscosity of 1.6 g / in 3 Wash coat load capacity and 8g / ft 3 It had a total PGM load, and the weight ratio of Pt:Pd:Rh was 1:1:2.

[0070] Performance testing The GPF-1 to GPF-5 prepared above were hydrothermally aged in HTA at 1050°C with 2% O2, the remainder N2, and 10% H2O. They were then tested on an engine bench for light-off against CO, THC, and NOx emissions. The results are shown in Tables 1 and 2, and Figures 1 to 3. From the T50 results, GPF-4 (from Example 1) showed comparable light-off to GPF-1 (from Comparative Example 1) for CO, THC, and NOx. GPF-4 contains a combination of Pt, Pd, and Rh, compared to GPF-1 (Comparative Example 1), which contains Pd and Rh. The total PGM load in GPF-4 and GPF-1 is the same. At the time of testing, GPF-4 offered a cost-benefit advantage over GPF-1 because Pt is cheaper than Pd. GPF-4 also showed an advantage over GPF-2 (from Comparative Example 2) in terms of light-off performance.

[0071] [Table 1]

[0072] [Table 2]

Claims

1. A catalytic wall flow filter for exhaust gases from a gasoline engine, A wall flow filter substrate having a porous wall and a first surface and a second surface defining a longitudinal direction between them, and a first plurality of channels and a second plurality of channels extending in the longitudinal direction, wherein the first plurality of channels are open on the first surface and closed on the second surface, and the second plurality of channels are open on the second surface and closed on the first surface, A first TWC coating in a plurality of first channels, comprising palladium, rhodium, a first oxygen storage capacity (OSC) material, and a first inorganic support, A second TWC coating in the second plurality of channels, comprising platinum, rhodium, a second OSC material, and a second inorganic support, Equipped with, The first TWC coating is applied from the first surface, The second TWC coating is applied from the second surface, A catalytic wall flow filter, wherein the first surface is the inlet surface of the catalytic wall flow filter, and the second surface is the outlet surface of the catalytic wall flow filter.

2. The catalyst wall flow filter according to claim 1, wherein the first TWC coating contains palladium and rhodium in a weight ratio of 10:1 to 1:

10.

3. The catalytic wall flow filter according to claim 1, wherein the first TWC coating contains palladium and rhodium in a weight ratio of 5:1 to 1:

5.

4. The catalytic wall flow filter according to claim 1, wherein the first TWC coating contains palladium and rhodium in a weight ratio of 2:1 to 1:

2.

5. The catalytic wall flow filter according to claim 1, wherein the second TWC coating contains platinum and rhodium in a weight ratio of 10:1 to 1:

10.

6. The catalytic wall flow filter according to claim 1, wherein the second TWC coating contains platinum and rhodium in a weight ratio of 5:1 to 1:

5.

7. The catalytic wall flow filter according to claim 1, wherein the second TWC coating contains platinum and rhodium in a weight ratio of 2:1 to 1:

2.

8. The first TWC coating is 2 to 10 g / ft ３ The PGM load is in the range of 2 to 10 g / ft, and the second TWC coating has a load of 2 to 10 g / ft ３ The catalyst wall flow filter according to claim 1, having a PGM loading amount within the range of [specify range].

9. The first TWC coating has a density of 3 to 6 g / ft ３ The total PGM load is in the range of 3 to 6 g / ft, and the second TWC coating has a load of 3 to 6 g / ft ３ The catalyst wall flow filter according to claim 1, having a total PGM load within the range.

10. The amount of the first TWC coating supported is 0.5 to 1.0 g / in. ３ The range is such that the amount of the second TWC coating supported is 0.5 to 1.0 g / in ３ The catalytic wall flow filter according to claim 1, which is within the range of [specified range].

11. The catalyst wall flow filter according to claim 1, wherein each of the first OSC material and the second OSC material independently comprises an OSC derived from a CeZr mixed oxide sol having a D90 of less than 1.3 microns.

12. The catalyst wall flow filter according to claim 1, wherein the first inorganic oxide support is alumina doped with 3 to 20% by weight of La, and the second inorganic oxide support is alumina doped with 3 to 20% by weight of La.

13. The catalyst wall flow filter according to claim 1, having a palladium-to-platinum weight ratio of 2:1 to 1:

2.

14. The catalytic wall flow filter according to claim 1, wherein the first TWC coating covers 50% to 55% of the length of the first plurality of channels, and the second TWC coating covers 50% to 55% of the length of the second plurality of channels.

15. A method for manufacturing a catalytic wall flow filter for exhaust gas treatment, (i) Forming a first wash coat slurry comprising palladium, rhodium, a first oxygen storage capacity (OSC) material, and a first inorganic support, (ii) Coating a wall flow filter substrate with the first wash coat slurry, wherein the wall flow filter substrate has a porous wall having a first surface and a second surface defining a longitudinal direction between them, and a first plurality of channels and a second plurality of channels extending in the longitudinal direction, wherein the first plurality of channels are open on the first surface and closed on the second surface, and the second plurality of channels are open on the second surface and closed on the first surface, and the first wash coat slurry is coated from the first surface. (iii) Forming a second washcoat slurry comprising platinum, rhodium, a second oxygen storage capacity (OSC) material, and a second inorganic support, (iv) Coating the wall flow filter substrate with the second wash coat slurry from the second surface of the wall flow filter substrate to form a washed wall flow filter substrate, (v) The washed-coated wall flow filter substrate is calcined to form a catalytic wall flow filter, Methods that include...

16. An exhaust treatment system for treating the flow of combustion exhaust gas from a gasoline direct injection engine, comprising the catalytic wall flow filter described in claim 1.

17. The exhaust treatment system according to claim 16, further comprising a TWC catalyst containing a TWC composition applied to a honeycomb flow-through substrate.

18. The discharge treatment system according to claim 17, wherein the TWC catalyst is located upstream of the catalyst wall flow filter.

19. A method for treating combustion exhaust gases from an externally ignited internal combustion engine, comprising contacting the exhaust gases with a catalytic wall flow filter according to claim 1, wherein the exhaust gases contain nitrogen oxides, carbon monoxide, hydrocarbons, and particulate matter.

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