Catalysed wall-flow filter

Abstract

Disclosed herein is a catalyzed wall-flow filter for exhaust gas from a gasoline engine. The catalyzed wall-flow filter includes a wall-flow filter substrate having porous walls and first and second faces defining a longitudinal direction therebetween, and a first plurality of channels and a second plurality of channels extending in the longitudinal direction. The first plurality of channels are open at the first face and closed at the second face, and the second plurality of channels are open at the second face and closed at the first face. The filter includes a first TWC coating including a first PGM composition, a first oxygen storage capacity (OSC) material, and a first inorganic carrier; and a second TWC coating including a second PGM composition, a second OSC material, and a second inorganic carrier.

Description

Technical Field

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

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

[0003] Driven by CO2 and / or fuel economy requirements, the number of GDI vehicles is steadily increasing. It is estimated that 60% of new gasoline vehicles in Europe in 2016 were GDI models. In North America, the proportion of GDI vehicles is also rapidly increasing—within nine years of its initial large-scale market adoption, its penetration rate in the United States has climbed to 48.5% of new light-duty vehicle sales. As the GDI vehicle fleet grows, its emissions raise public health concerns and are a potential major source of particulate pollution in densely populated urban areas.

[0004] Early GPF applications included uncoated GPFs positioned downstream of three-way catalytic converters (TWC). As technology matured, GPFs were also coated with three-way catalysts. This catalyst-coated GPF configuration is sometimes referred to as a four-way catalytic converter. See, for example, US10,625,243B2, US 2020 / 0353410A1, US2019 / 0168162A1, and US2009 / 0193796A1. However, combining TWC coatings with the filter body introduces additional challenges, such as excessive back pressure and requirements for minimum CO, NOx, and HC conversion characteristics. Furthermore, cost must be considered to achieve an optimal balance between performance and cost.

[0005] Three-way catalytic converters are designed 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 gases from an engine operating at or near its stoichiometric point. As is well known in the art, the amounts of carbon monoxide, unburned hydrocarbons, and nitrogen oxides emitted when gasoline fuel is burned in a forced-ignition (e.g., spark-ignition) internal combustion engine are primarily influenced by the air-fuel ratio in the combustion cylinder. Exhaust gases with a stoichiometric equilibrium composition consist of oxidized gases (NO...) xThe concentrations of O2 and reducing gases (HC and CO) in the exhaust gas are essentially matched. The air-fuel ratio of the exhaust gas composition that produces this stoichiometric equilibrium is typically 14.7:1.

[0006] The active components in a typical TWC include one or both of the following: platinum and palladium bonded to rhodium supported on a high surface area oxide, and oxygen storage capacity (OSC) materials.

[0007] In theory, it should be possible to achieve stoichiometric balance of O2 and NO in the waste gas composition. x The complete conversion of CO and HC into CO2, H2O, and N2 (as well as residual O2) is the task of TWC. Therefore, ideally, the engine should operate in a way that produces an exhaust gas composition that achieves stoichiometric equilibrium between the air and fuel ratio of the combustion mixture.

[0008] The compositional balance between oxidizing and reducing gases in exhaust gas is defined by the λ value of the exhaust gas, which can be defined according to the following formula:

[0009] λ = (Actual engine air-fuel ratio) / (Stoichiometric air-fuel ratio)

[0010] Wherein, a value of λ = 1 indicates a stoichiometric (or stoichiometric) exhaust gas composition, where a value > 1 indicates an excess of O2 and NOx and the composition is described as "lean," and where a value < 1 indicates an excess of HC and CO and the composition is described as "rich." In the art, the air-fuel ratio during engine operation is also commonly referred to as "stoichiometric," "lean," or "rich," depending on the exhaust gas composition produced by the air-fuel ratio.

[0011] It should be understood that when the exhaust gas composition is stoichiometric or lean, TWC is used to reduce NO. xThe efficiency of reducing to N2 is low. Similarly, when the exhaust gas composition is rich, the TWC's ability to oxidize CO and HC is low. Therefore, the challenge is to keep the composition of the exhaust gas flowing into the TWC as close as possible to the stoichiometric composition. Of course, when the engine is in 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 instantaneously according to the load demand applied to the engine by the driver. This makes controlling the air-fuel ratio to produce stoichiometric exhaust gas for the three-way conversion particularly difficult. In practice, the air-fuel ratio is controlled by the engine control unit, which receives information about the exhaust gas composition from the exhaust oxygen (EGO) (or λ) sensor: a so-called closed-loop feedback system. This system is characterized by the air-fuel ratio oscillating (or perturbing) between a slightly rich and slightly lean point of stoichiometry (or control setting) due to the time lag associated with adjusting the air-fuel ratio. This perturbation is characterized by the amplitude and response frequency (Hz) of the air-fuel ratio.

[0012] When the exhaust gas composition is slightly richer than the set value, a small amount of oxygen is needed to consume unreacted CO and HC, i.e., to bring the reaction closer to stoichiometry. Conversely, when the exhaust gas becomes slightly leaner, an excess of oxygen is required. This is achieved by developing OSC materials that release or absorb oxygen during disturbances. Commonly used OSC materials in modern TWC are cerium oxides or cerium-containing mixed oxides, such as CeZr mixed oxides.

[0013] There is a need to develop technologies that can effectively convert CO, NOx, and HC and reduce particulate matter in exhaust gases from gasoline engines. Summary of the Invention

[0014] One aspect of this disclosure relates to a catalytic wall-flow filter for exhaust gases from a gasoline engine, the catalytic wall-flow filter comprising:

[0015] A wall-flow filter substrate having a porous wall and having a first surface and a second surface, defining a longitudinal direction between the first surface and the second surface; 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 wherein the second plurality of channels are open at the second surface and closed at the first surface.

[0016] A first TWC coating in a first plurality of channels, the first TWC coating comprising a first PGM composition, a first oxygen storage capacity (OSC) material and a first inorganic carrier;

[0017] A second TWC coating in a second plurality of channels, the second TWC coating comprising a second PGM composition, a second OSC material and a second inorganic carrier;

[0018] The first PGM composition comprises a rhodium amounting to 50% to 95% by weight relative to the total weight of the first PGM composition;

[0019] The second PGM composition comprises palladium in an amount of 90% to 99% by weight relative to the total weight of the second PGM composition;

[0020] The first TWC coating is applied from the first surface;

[0021] The second TWC coating is applied from the second side;

[0022] The first side is the inlet side of the catalytic wall flow filter, and the second side is the outlet side of the catalytic wall flow filter.

[0023] Another aspect of this disclosure is an exhaust treatment system for treating combustion exhaust gas from a gasoline direct injection engine, the system comprising a catalytic wall-flow filter as disclosed herein. Preferably, the exhaust system includes a TWC catalyst and a catalytic wall-flow integral filter, wherein the TWC catalyst is upstream of the catalytic wall-flow integral filter.

[0024] According to another aspect, the present invention provides a method for treating combustion exhaust gases from a forced-ignition internal combustion engine, the combustion exhaust gases containing nitrogen oxides, carbon monoxide, hydrocarbons and particulate matter, the method comprising contacting the exhaust gases with a catalytic wall-flow filter as disclosed herein. Detailed Implementation

[0025] This disclosure will now be described further. In the following paragraphs, different aspects / implementations of this disclosure are defined in more detail. Unless expressly stated to the contrary, each aspect / implementation so defined may be combined with any other aspect / implementation or multiple aspects / implementations. In particular, any feature indicated as preferred or advantageous may be combined with one or more other features indicated as preferred or advantageous.

[0026] One aspect of this disclosure relates to a catalytic wall-flow filter for exhaust gases from a gasoline engine, the catalytic wall-flow filter comprising:

[0027] A wall-flow filter substrate having a porous wall and having a first surface and a second surface, defining a longitudinal direction between the first surface and the second surface; 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 wherein the second plurality of channels are open at the second surface and closed at the first surface.

[0028] A first TWC coating in a first plurality of channels, the first TWC coating comprising a first PGM composition, a first oxygen storage capacity (OSC) material and a first inorganic carrier;

[0029] A second TWC coating in a second plurality of channels, the second TWC coating comprising a second PGM composition, a second OSC material and a second inorganic carrier;

[0030] The first PGM composition comprises a rhodium amounting to 50% to 95% by weight relative to the total weight of the first PGM composition;

[0031] The second PGM composition comprises palladium in an amount of 90% to 99% by weight relative to the total weight of the second PGM composition;

[0032] The first TWC coating is applied from the first surface;

[0033] The second TWC coating is applied from the second side;

[0034] The first side is the inlet side of the filter, and the second side is the outlet side of the filter.

[0035] The substrate of the wall-flow filter can be ceramic, such as silicon carbide, cordierite, aluminum nitride, silicon nitride, aluminum titanate, alumina, mullite, cesium garnet, or composite segments containing any two or more of these. Cordierite, magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0036] Suitable wall-flow filter substrates for use in this invention typically have an average pore size of 8 μm to 45 μm (e.g., 8 μm to 25 μm, 10 μm to 20 μm). Pore size is well known in the art, and suitable measurement techniques are known to those skilled in the art. Wall-flow filter substrates can have a porosity of 40% to 75% (e.g., 45% to 70%). The average pore size can be determined using conventional methods such as mercury intrusion porosimetry and X-ray tomography.

[0037] The catalytic wall-flow filter includes a first TWC coating in a first plurality of channels, the first TWC coating comprising a first PGM composition, a first oxygen storage capacity (OSC) material, and a first inorganic support.

[0038] As used in this article, “PGM” refers to “platinum group metals”. The term “platinum group metals” generally refers to metals selected from the following group: Ru, Rh, Pd, Os, Ir, and Pt.

[0039] The first PGM composition preferably comprises Rh and Pd. The first PGM composition may also comprise Pt.

[0040] The first PGM composition comprises, relative to the total weight of the first PGM composition, 50% to 95% by weight, preferably 60% to 90% by weight, more preferably 65% ​​to 85% by weight, and even more preferably 70% to 80% by weight of Rh.

[0041] The second PGM composition comprises, relative to the total weight of the second PGM composition, 90% to 99% by weight, preferably 91% to 98% by weight, more preferably 92% to 97% by weight, and even more preferably 93% to 96% by weight of palladium. The second PGM composition preferably comprises Rh and Pd. The second PGM composition may also comprise Pt.

[0042] "Oxygen storage capacity" refers to the ability of a material used as an oxygen storage material in a catalyst composition to store oxygen under lean conditions and release oxygen under rich conditions.

[0043] 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 cerium dioxide or a mixed oxide comprising cerium dioxide. Preferably, the first OSC material and the second OSC material each comprise 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. As used herein, the term "mixed oxide" generally refers to a mixture of oxides in single-phase form, as is commonly known in the art.

[0044] The amount of OSC material in the first or second TWC coating can be from 5% to 90% by weight, preferably from 10% to 80% by weight, relative to the total weight of the coating.

[0045] In some embodiments, each of the first OSC material and the second OSC material independently comprises an OSC derived from a CeZr mixed oxide sol with a D90 of less than 1.3 micrometers. The CeZr mixed oxide sol comprises CeZr mixed oxides (CeZr mixed oxide particles or CeZr mixed oxide nanoparticles) dispersed in an aqueous medium.

[0046] Particle size distribution can be characterized by D10, D50, and D90 measurements. In each case, this number represents the percentage of particles smaller than the stated value. In other words, a D90 of 100 micrometers means that 90% of the particles have a diameter less than 100 micrometers. By understanding D10 and D90, the range of particles in the particle distribution can be defined. Characterizing the particle size of a sample through its D10 and D90 values ​​typically defines the width of the particle size distribution. The closer these values ​​are, the narrower the particle size distribution.

[0047] The particle size measurements necessary to obtain the D10, D50, and D90 values ​​for CeZr mixed oxide sols and / or particulate inorganic oxides can be obtained using laser diffraction particle size analysis with a Malvern Mastersizer 3000, a volume-based technique (i.e., D50 and D90 can also be referred to as D...). V 50 and D V The particle size distribution is determined by applying a mathematical Mie theory model (or D(v, 0.50) and D(v, 0.90)). The laser diffraction system works by determining the particle diameter based on a spherical approximation. For particle size measurements performed by laser diffraction particle size analysis, a diluted sample is prepared by sonicating in distilled water without surfactant at 35 watts for 30 seconds.

[0048] In some implementations, the D90 of the CeZr mixed oxide sol may be less than 1.2 micrometers, or less than 1.1 micrometers, or less than 1.0 micrometers, 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.

[0049] In some other embodiments, the D90 of the CeZr mixed oxide sol can be between 1.2 μm and 1.3 μm, or between 1.1 μm and 1.2 μm, or between 1.0 μm and 1.1 μm, or between 900 nm and 1.0 μm, or between 800 nm and 900 nm, or between 700 nm and 800 nm, or between 600 nm and 700 nm, or between 500 nm and 600 nm, or between 400 nm and 500 nm, or between 300 nm and 400 nm, or between 200 nm and 300 nm, or between 100 nm and 200 nm.

[0050] CeZr mixed oxide sol can have a D50 between 100 nm and 700 nm, preferably between 200 nm and 600 nm, and more preferably between 300 nm and 400 nm.

[0051] 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 the overall ensemble of particles measured by dynamic light scattering (DLS). The Z-mean originates from cumulative analysis of the correlation curves of the measurements, where individual particle sizes are assumed and a single exponential fit is applied to the autocorrelation function. The particle size measurements necessary to obtain the Z-mean particle size of CeZr mixed oxide sols can be obtained by dynamic light scattering particle size analysis using a Malvern Zetasizer Nano. All tests were performed in a diluted aqueous medium, where the harmonic mean hydrodynamic diameter of the spheres with equivalent diffusivity was determined by cumulative analysis of the time dependence of light scattered by randomly moving particles according to the Stokes-Einstein Equation.

[0052] The Z-average particle size of the CeZr mixed oxide sol is preferably between 150 nm and 350 nm, and more preferably between 230 nm and 310 nm.

[0053] The first and second inorganic oxide supports may each be oxides of elements from Groups 2, 3, 4, 5, 13, and 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 exhaust. The first and second inorganic oxide supports may each be selected from the group consisting of alumina, silicon dioxide, titanium dioxide, and mixed or composite oxides thereof. More preferably, the inorganic oxide support is alumina.

[0054] Inorganic oxide supports, such as aluminum, may be doped with dopants. Dopants may be selected from 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 can be from 1% to 30% by weight, preferably from 2% to 25% by weight, more preferably from 3% to 20% by weight.

[0055] The D50 of the first or second inorganic material can be in the range of 0.1 μm to 100 μm, preferably in the range of 0.1 μm to 50 μm.

[0056] 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.

[0057] 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.

[0058] The OSC material and inorganic oxide carrier in the first or second TWC coating may have the following weight ratio: 10:1 to 1:10, preferably 5:1 to 1:5, more preferably 3:1 to 1:3.

[0059] In some implementations, the second TWC coating loading includes a barium component.

[0060] Typically, a carrier coating slurry is used to apply a first TWC coating and a second TWC coating to a wall-flow filter substrate. A suitable coating process is described in WO1999047260. The first TWC coating is applied from a first side (inlet side). The second TWC coating is applied from a second side (outlet side). Preferably, the second TWC coating is applied from the second side (outlet side) before the first TWC coating is applied from the first side (inlet side) of the wall-flow filter substrate.

[0061] After applying one or both of the first and second TWC coatings to the wall-flow filter substrate, it is preferable to dry and / or calcine the wall-flow filter substrate containing one coating before applying the other coating. The drying step can be performed at a lower temperature (such as 100°C to 200°C) prior to calcination. Calcination is conventional in the art and can be carried out under normal conditions.

[0062] The first TWC coating preferably covers 50% to 90% of the length of the first plurality of channels, more preferably 60% to 80%.

[0063] The second TWC coating preferably covers 30% to 70% of the length of the second plurality of channels, more preferably 40% to 60%.

[0064] The first TWC coating and the second TWC coating can each be an in-wall coating, an on-wall coating, or a combination of an in-wall coating and an on-wall coating.

[0065] The first TWC coating loading can be 0.4 g / in. 3 Up to 0.7g / in 3 Preferably 0.45 g / in 3 Up to 0.65g / in 3 Within the range. The first TWC coating load is defined as the weight of the first TWC coating relative to the total volume of the calcined wall flow filter.

[0066] The second TWC coating loading can be 0.4 g / in. 3 Up to 0.7g / in 3 Preferably 0.45 g / in 3 Up to 0.65g / in 3 Within the range.

[0067] The first TWC coating can have a concentration of 2g / ft. 3 Up to 12g / ft 3 Within the range, preferably within 3g / ft 3 Up to 10g / ft 3 Within the range, more preferably within 4g / ft 3 Up to 8g / ft 3 Total PGM load within the range.

[0068] The second TWC coating can have a strength of 10 g / ft. 3 Up to 40g / ft 3 Within the range, preferably within 15 g / ft 3 Up to 30g / ft 3 Within the range, more preferably within 20 g / ft 3 Up to 25g / ft 3 Total PGM load within the range.

[0069] Another aspect of this disclosure is an exhaust treatment system for treating combustion exhaust gas from a gasoline direct injection engine, the system comprising a catalytic wall-flow filter as disclosed herein. The exhaust system may include additional components, such as a TWC catalyst containing a TWC composition applied to a honeycomb straight-through substrate and disposed upstream or downstream of the catalytic wall-flow filter according to the invention.

[0070] Preferably, the exhaust system includes a TWC catalyst and a catalytic wall-flow filter as disclosed herein, wherein the TWC catalyst is upstream of the catalytic wall-flow filter.

[0071] Catalytic wall-flow filters are effective in reducing hydrocarbon, CO, NOx and particulate emissions.

[0072] According to another aspect, the present invention provides a method for treating combustion exhaust gases from a forced-ignition internal combustion engine, the combustion exhaust gases containing nitrogen oxides, carbon monoxide, hydrocarbons and particulate matter, the method comprising contacting the exhaust gases with a catalytic wall-flow filter as disclosed herein.

[0073] Example 1: GPF-1

[0074] TWC carrier coating slurry (“Slurry-A”) was prepared by mixing rhodium nitrate, palladium nitrate, a CeZr mixed oxide sol with a weight ratio of ZrO2 to CeO2 of approximately 2:1 and a D90 < 1 μm, a La-stabilized alumina component with a D90 of 5 μm, barium hydroxide, and water. The solids content was approximately 25%.

[0075] Slurry-A was applied to the outlet surface of a cordierite wall-flow filter substrate (5.2 × 4 inches, 300 / 8, average pore size 15 microns, porosity 65%) using the coating method described in WO1999 / 47260. The outlet carrier coating was approximately 55% of the substrate length and had a content of 0.6 g / in. 3 The carrier coating loading (after calcination). The outlet carrier coating has 24 g / ft. 3 The total PGM load, where the Pd:Rh weight ratio is 47:1.

[0076] Another TWC carrier coating slurry (“Slurry-B”) was prepared by mixing a CeZr mixed oxide sol of rhodium nitrate, palladium nitrate, ZrO2 and CeO2 in a weight ratio of approximately 2:1 and with a D90 < 1 μm, and a La-stabilized alumina component with a D90 of 5 μm, and water. The solids content was approximately 25%.

[0077] Slurry-B is applied to the inlet surface of the wall-flow filter substrate with the pre-coated outlet channel. The inlet carrier coating is approximately 70% of the substrate length and has a content of 0.6 g / in. 3 The carrier coating loading (after calcination). The inlet carrier coating has a loading of 6 g / ft. 3 The total PGM load, where the Pd:Rh weight ratio is 1:3.

[0078] The coated filter substrate was dried at 100°C and calcined at 500°C for 1 hour. The total PGM loading of GPF-1, including both inlet and outlet coatings, was 30 g / ft. 3 The Pd:Rh weight ratio is 5:1.

[0079] Comparative Example 2: GPF-2

[0080] TWC carrier coating slurry was prepared by mixing a CeZr mixed oxide sol of rhodium nitrate, palladium nitrate, ZrO2, and CeO2 in a weight ratio of approximately 2:1 and with a D90 < 1 μm, and a La-stabilized alumina component with a D90 of 5 μm, barium hydroxide, and water. The solids content was 24%. The coating was applied from each end of a cordierite wall-flow filter substrate (5.2 × 4 inches, 300 / 8, average pore size 15 μm, porosity 65%) using the coating method described in WO1999 / 47260. The coating length from each side was approximately 58% of the total substrate length. The amount of carrier coating slurry applied to the inlet and outlet channels was the same. The coated filter substrate was dried at 100°C and calcined at 500°C for 1 hour. The coated catalytic filter had a solids content of 1.6 g / in. 3 The carrier coating loading is 1.2 g / in. 3 CeZr mixed oxide and 0.4 g / in3 La-stabilized alumina component. The PGM loading of GPF-2 is 30 g / ft. 3 The Pd:Rh weight ratio is 5:1.

[0081] Example 3: Performance Testing

[0082] Using an engine bench aging cycle, with the bed temperature controlled at 1050°C, each of GPF-1 and GPF-2 was aged for 120 hours at a close-coupled location downstream of the TWC catalyst. Each filter was installed under the floor of a 2018MY 2.0L passenger car with a direct-injection gasoline engine. Each filter was evaluated in at least three RDE-erosion cycles with cold starts, measuring the reduction in gaseous emissions relative to a reference catalyst. Back pressure differentials and conversion efficiencies for gaseous HC, CO, and NOx emissions were determined using sensors installed upstream and downstream of the filters and upstream and downstream of the close-coupled TWC. The results presented in Table 1 below show that GPF-1 delivers lower levels of NOx emissions compared to GPF-2.

[0083] In addition, SCAT reactor aging was performed on GPF-1 and GPF-2 cores (1×4") at 1000°C using a 4-mode aging cycle. The SCAT reactor performance evaluation of the aged cores showed significant differences in NOx ignition, as shown in Table 1.

[0084] Table 1

[0085] Filter NOx emissions (g / mile) NOx ignition T50 (°C) GPF-2 (Comparative Example) 0.14 305 GPF-1 0.1 270

Claims

1. A catalytic wall-flow filter for exhaust gas from a gasoline engine, the catalytic wall-flow filter comprising: A wall-flow filter substrate having a porous wall and having a first surface and a second surface, defining a longitudinal direction between the first surface and the second surface; 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 wherein the second plurality of channels are open at the second surface and closed at the first surface; A first TWC coating in the first plurality of channels, the first TWC coating comprising a first PGM composition, a first OSC material and a first inorganic carrier; The second TWC coating in the second plurality of channels, the second TWC coating comprising a second PGM composition, a second OSC material and a second inorganic carrier; The first PGM composition comprises a amount of rhodium ranging from 50% to 95% by weight relative to the total weight of the first PGM composition; The second PGM composition comprises palladium in an amount of 90% to 99% by weight relative to the total weight of the second PGM composition; The first TWC coating is applied from the first surface; The second TWC coating is applied from the second surface; 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 catalytic wall-flow filter according to claim 1, wherein the first PGM composition comprises Rh and Pd.

3. The catalytic wall-flow filter of claim 1, wherein the first PGM composition comprises an amount of Rh of 70% to 80% by weight relative to the total weight of the first PGM composition.

4. The catalytic wall-flow filter according to claim 1, wherein the second PGM composition comprises Rh and Pd.

5. The catalytic wall-flow filter of claim 1, wherein the second PGM composition comprises 93% to 96% by weight of palladium relative to the total weight of the second PGM composition.

6. The catalytic wall-flow filter of 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 with a D90 of less than 1.3 microns.

7. The catalytic wall-flow filter according to claim 1, wherein the first inorganic support is alumina doped with 3% to 20% by weight of La.

8. The catalytic wall-flow filter according to claim 1, wherein the second inorganic support is alumina doped with 3% to 20% by weight of La.

9. The catalytic wall-flow filter of claim 1, wherein the first TWC coating covers 60% to 80% of the length of the first plurality of channels.

10. The catalytic wall-flow filter of claim 1, wherein the second TWC coating covers 40% to 60% of the length of the second plurality of channels.

11. An emission treatment system for treating combustion exhaust gas from a gasoline direct injection engine, the system comprising a catalytic wall-flow filter according to claim 1.

12. The emission treatment system of claim 11, further comprising a TWC catalyst containing a TWC composition applied to a honeycomb through-type substrate.

13. The emission treatment system of claim 12, wherein the TWC catalyst is disposed upstream of the catalytic wall flow filter.

14. A method for treating combustion exhaust gas from a forced-ignition internal combustion engine, the combustion exhaust gas containing nitrogen oxides, carbon monoxide, hydrocarbons, and particulate matter, the method comprising contacting the exhaust gas with a catalytic wall-flow filter according to claim 1.