Method for producing a gasoline particulate filter

Abstract

A method for making a gasoline particulate filter is disclosed. The method includes forming a washcoat slurry, coating a wall-flow filter substrate with the washcoat slurry to form a washcoated substrate, and calcining the washcoated substrate to form a gasoline particulate filter. The washcoat slurry includes a platinum group metal component consisting of Pt and Rh, an oxygen storage capacity material, and a carboxylate ion.

Description

[Technical field]

[0001] The present invention relates to a method for providing a catalyzed wall-flow filter suitable for use in automotive exhaust treatment systems for vehicles, particularly exhaust treatment systems for positive ignition internal combustion engines such as gasoline spark ignition engines. In particular, the present invention provides a method for producing a catalyzed wall-flow filter having improved catalytic activity and reduced backpressure. [Background technology]

[0002] Gasoline particulate filters (GPFs) are an exhaust aftertreatment technology developed to control particulate emissions from gasoline direct injection (GDI) engines.

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

[0004] Most early GPF applications involved an uncoated GPF positioned downstream of a three-way catalyst (TWC). As the technology matured, GPFs have also been coated with a three-way catalyst. This catalyst-coated GPF configuration is sometimes referred to as a four-way catalyst. However, the combination of a TWC coating on the filter body introduces additional issues such as excessive backpressure, and there are requirements for minimal CO, NOx, and HC conversion characteristics. In addition, cost must be considered as it must provide the best possible balance between performance and cost.

[0005] A three-way catalyst 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 gases from an engine operating at or near the stoichiometric point. As is well known in the art, the amount of carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx) emitted when gasoline fuel is burned in a spark-ignited (e.g., spark-ignited) internal combustion engine is primarily affected by the air-fuel ratio in the combustion can. Exhaust gases with a stoichiometrically balanced composition produce a high concentration of oxidizing gases (NO x and O2) and reducing gases (HC and CO) are substantially matched in concentration. The air-fuel ratio that produces this stoichiometrically balanced exhaust gas composition is typically given as 14.7:1.

[0006] The active components in a typical TWC include one or both of platinum and palladium in combination with rhodium supported on a high surface area oxide, or even palladium alone (no rhodium), and an oxygen storage capacity (OSC) material.

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

[0008] A way to define the compositional balance between oxidizing and reducing gases in the 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 >1 represents an excess of O2 and NOx and the composition is described as "lean", and a lambda value <1 represents an excess of HC and CO and the composition is described as "rich". It is also common in the art to refer to air / fuel ratios at which an engine operates as "stoichiometric", "lean" or "rich", depending on the exhaust gas composition it produces.

[0009] NO using TWC x It should be understood that the reduction of CO to N2 is less efficient when the exhaust gas composition is lean or stoichiometric. Similarly, the TWC is less capable of oxidizing CO and HC when the exhaust gas composition is rich. The challenge is therefore to maintain the composition of the exhaust gas entering the TWC as close to stoichiometric as possible. Naturally, it is relatively easy to ensure that the air-fuel ratio is stoichiometric when the engine is in steady state. However, when the engine is used to propel a vehicle, the amount of fuel required varies temporarily depending on the load demand 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 the three-way conversion. In practice, the air-fuel ratio is controlled by an engine control unit that receives information about the exhaust gas composition from an exhaust gas oxygen (EGO) (or lambda) sensor, a so-called closed-loop feedback system. Such systems are characterized by an oscillation (or perturbation) of the air-fuel ratio between a slightly rich stoichiometric (or control set) point and slightly lean due to the time lag associated with adjusting the air-fuel ratio, the perturbation being characterized by the amplitude and response frequency (Hz) of the air-fuel ratio.

[0010] When the exhaust gas composition is slightly richer than the set point, a small amount of oxygen is needed to consume the 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 the development of OSC materials that release or absorb oxygen during perturbation. The most commonly used OSC material in modern TWCs is cerium oxide (CeO2) or mixed oxides containing cerium, e.g., Ce / Zr mixed oxide.

[0011] It is an object of the present invention to provide an improved method for producing GPFs, addressing problems associated with the prior art and / or at least providing a commercially viable alternative. Summary of the Invention

[0012] One aspect of the present disclosure is directed to a method of manufacturing a gasoline particulate filter (GPF), comprising: (i) forming a washcoat slurry; (ii) coating a wall-flow filter substrate with the washcoat slurry to form a washcoated substrate; and (iii) calcining the washcoated substrate to form a GPF, wherein the washcoat slurry comprises: (a) a platinum group metal (PGM) component consisting of Pt and Rh; (b) an oxygen storage capacity (OSC) material; and (c) a carboxylate ion.

[0013] Another aspect of the present disclosure is directed to a pre-calcined GPF precursor comprising a washcoated wall-flow filter substrate comprising a washcoat, the washcoat comprising: (a) a platinum group metal (PGM) component consisting of Pt and Rh; (b) an oxygen storage capacity (OSC) material; and (c) a carboxylate ion.

[0014] Another aspect of the present disclosure is directed to a method of manufacturing a gasoline combustion and exhaust gas treatment system, the method including: (a) providing a gasoline engine having an exhaust manifold; (b) manufacturing a GPF according to the methods described herein; and (c) forming an exhaust gas treatment system including the GPF and connecting the exhaust gas treatment system to the exhaust manifold of the gasoline engine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present disclosure will now be further described. In the following sections, different aspects / embodiments of the present disclosure are defined in more detail. Each aspect / embodiment so defined may be combined with any other aspect / embodiment or aspect / embodiment, unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0016] One aspect of the present disclosure is directed to a method of manufacturing a gasoline particulate filter (GPF) comprising: (i) forming a washcoat slurry; (ii) coating a wall-flow filter substrate with the washcoat slurry to form a washcoated substrate; and (iii) calcining the washcoated substrate to form a GPF, wherein the washcoat slurry comprises: (a) a platinum group metal (PGM) component consisting of Pt and Rh; (b) an oxygen storage capacity (OSC) material; and (c) a carboxylate ion.

[0017] The method includes forming a washcoat slurry, the washcoat slurry including platinum group metal (PGM) components consisting of Pt and Rh. Suitable precursors of Pt and Rh include salts containing these metals, such as platinum nitrate and rhodium nitrate.

[0018] The amount of PGM (ie, the sum of Pt and Rh) in the washcoat slurry can be 0.005 to 10 wt %, preferably 0.001 to 5 wt %, and more preferably 0.05 to 3.0 wt %, based on the total weight of the washcoat slurry.

[0019] The weight ratio of Pt to Rh may be from 1:10 to 10:1, preferably from 1:2 to 2:1.

[0020] The washcoat slurry does not contain any other PGMs, in particular the washcoat slurry does not contain any Pd.

[0021] The washcoat slurry includes an oxygen storage capacity (OSC) material. "Oxygen storage capacity" refers to the ability of a material used as an oxygen storage capacity material in a catalyst to store oxygen under lean conditions and release oxygen under rich conditions.

[0022] The OSC material may be ceria or a mixed oxide including ceria. Preferably, the OSC material comprises a mixed oxide of cerium, 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. The term "mixed oxide" as used herein generally refers to a mixture of oxides in a single phase, as is conventionally known in the art.

[0023] The amount of OSC material in the washcoat slurry can be from 5 to 50 wt %, preferably from 10 to 30 wt %, based on the total weight of the washcoat slurry.

[0024] The washcoat slurry comprises carboxylate ions. Preferably, the carboxylate ions are selected from the group consisting of citrate, malate, malonate, succinate, tartrate, glutarate, tartronate, oxalate, lactate, and glycolate ions, and mixtures thereof, more preferably citrate, malate, malonate, succinate, tartrate, glutarate, tartronate, and oxalate ions, and mixtures thereof, even more preferably citrate and / or malonate ions. Citrate ions are most preferred.

[0025] Preferably, the molar ratio of carboxylate ions to Pt ions in the washcoat slurry is from 1:1 to 100:1, more preferably from 5:1 to 50:1, and most preferably from 10:1 to 25:1.

[0026] Preferably, the washcoat slurry is substantially free of Ba. The present inventors have found that unlike GPFs containing Pd and Rh, the inclusion of Ba ions adversely affects the performance of GPFs containing Pt and Rh. That is, surprisingly, removing Ba improves the TWC effect of GPFs.

[0027] The washcoat slurry may further comprise an inorganic oxide support. The inorganic oxide support may be an oxide of an element of Groups 2, 3, 4, 5, 13, and 14. The inorganic oxide support is preferably a refractory oxide that exhibits chemical and physical stability at elevated temperatures, such as those associated with the exhaust of a gasoline engine. The inorganic oxide support may be selected from the group consisting of alumina, silica, titania, and mixed or composite oxides thereof. More preferably, the inorganic oxide support is alumina.

[0028] The inorganic oxide support may be doped with a dopant. The dopant may 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 1-30% by weight, preferably 2-25% by weight, more preferably 3-20% by weight.

[0029] The OSC material and the inorganic oxide support in the washcoat slurry 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.

[0030] The washcoat slurry typically contains water as the solvent. Other solvents or mixtures of water with other solvents such as alcohols may be used.

[0031] The washcoat slurry typically has a solids content of 15-40% by weight, more preferably 20-35% by weight.

[0032] The method further includes coating a wall-flow filter substrate with the washcoat slurry to form a washcoated substrate.

[0033] Wall-flow filter substrates are well known in the art. Wall-flow filter substrates have a first face and a second face defining a longitudinal direction therebetween, and a first and a second plurality of channels extending longitudinally. The first plurality of channels are open at the first face and closed at the second face, the channels of the first plurality of channels being defined in part by a channel wall. The second plurality of channels are open at the second face and closed at the first face, the channels of the second plurality of channels being defined in part by a channel wall. The channel walls between the channel walls of the first plurality of channels and the channel walls of the second plurality of channels are porous.

[0034] The wall-flow filter substrate may be a ceramic, such as silicon carbide, cordierite, aluminum nitride, silicon nitride, aluminum titanate, alumina, mullite, pollucite, or a composite material comprising segments of any two or more of these, with cordierite, magnesium aluminosilicate, and silicon carbide being particularly preferred.

[0035] Wall-flow filter substrates suitable for use in the present invention typically have an average pore size of 8 to 45 μm, for example 8 to 25 μm, 10 to 20 μm, or 10 to 15 μm. Pore sizes are well known to those skilled in the art and suitable 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% or 50 to 65%. The average pore size may be determined using mercury porosimetry and X-ray tomography according to conventional methods.

[0036] The coating may be performed by spraying and / or dipping the wall-flow filter substrate. Preferably, the coating is applied to at least one of the inlet and outlet channels of the wall-flow filter substrate. More preferably, the coating is applied to both the inlet and outlet channels. One suitable coating procedure is described in WO1999047260.

[0037] The method further includes calcining the washcoated substrate to form a GPF. Calcination may be preceded by a drying step at a lower temperature (such as 100-200° C.). Calcination is routine in the art and may be carried out under conventional conditions.

[0038] After calcination, the Pt loading in the GPF is generally 1 g / ft 3 ~50g / ft 3 , more preferably 2 g / ft 3 ~20g / ft 3 The Rh loading in the GPF is generally 1 g / ft 3 ~50g / ft 3 , more preferably 2 g / ft3 ~20g / ft 3 The washcoat loading of the calcined GPF is typically 0.2 g / in 3 ~5g / in 3 , more preferably 0.5 g / in 3 ~3g / in 3 It is.

[0039] Both Pt and Pd are known to have catalytic activity for purifying components in exhaust gas. Moreover, in fact, Pd has become much more expensive than Pt in recent years. In fact, at the time of drafting this application, the price of Pd is generally two to three times the price of Pt. Therefore, there is a movement to reduce the amount of Pd used in catalytic devices.

[0040] The use of Pt is generally considered to be less effective. In fact, Pt has less activity when exchanged for Pd because it has fewer active sites. The Pt atomic weight is nearly twice that of Pd, so in a given weight of PGM, the molar amount of Pt is only about half that of Pd. Pt is also known to have weaker thermal stability due to its higher volatility pressure compared to Pd at high temperatures. This is particularly important for GPFs compared to components used in diesel engine exhaust systems, since the temperatures encountered are generally higher. This is also important in filters compared to flow-through substrates, since there are intermittent high temperature regeneration steps used to burn off accumulated particulate matter.

[0041] The inventors have found that, if certain additional steps are taken, these shortcomings can be overcome and a Pt and Rh-containing GPF can be produced that can perform even better than a Pd and Rh-containing GPF. In particular, the inventors have found that the inclusion of carboxylate ions, for example, added as carboxylic acid or suitable alkali metal salt or alkaline earth metal salt in the washcoat slurry, provides a GPF with improved catalytic performance and reduced back pressure. Without wishing to be bound by theory, it is believed that the enhanced Pt performance may be the result of the carboxylate generating more porosity in the coated filter. Note that the improvement in OSC performance also increases.

[0042] Another aspect of the present disclosure is directed to a pre-calcined GPF precursor comprising a washcoated wall-flow filter substrate comprising a washcoat, the washcoat comprising: (a) a platinum group metal (PGM) component consisting of Pt and Rh; (b) an oxygen storage capacity (OSC) material; and (c) a carboxylate ion.

[0043] The pre-calcined precursor may be obtained by the method described herein without calcination. Thus, all aspects of the method described herein apply. The pre-calcined precursor, of course, contains carboxylate ions that would otherwise be burned in the calcination process. Preferably, the molar ratio of carboxylate ions to Pt ions in the washcoat of the pre-calcined GPF precursor is 1:1 to 100:1, more preferably 5:1 to 50:1, and most preferably 10:1 to 25:1.

[0044] According to a further aspect, there is provided a method of manufacturing a gasoline combustion and exhaust gas treatment system, the method including: (a) providing a gasoline engine having an exhaust manifold; (b) manufacturing a GPF according to the methods described herein; and (c) manufacturing an exhaust gas treatment system including the GPF and connecting the exhaust gas treatment system to the exhaust manifold. EXAMPLES

[0045] Cold Flow Back Pressure Test Comparative catalyst A A washcoat slurry was prepared containing Pd and Rh supported on cerium-zirconium mixed oxide and La-stabilized alumina, Ba promoter, and water. The washcoat slurry was coated from both the inlet and outlet faces of a cordierite wall-flow honeycomb filter substrate (132.1 mm x 127 mm; 300 cells / sq. in; 12,000ths of an inch wall thickness; 19 μm average pore size; 63% porosity) using the coating procedure described in WO1999047260A1. The coating length on both the inlet and outlet channels is about 55% of the substrate length. The coated substrate was dried at 90°C and calcined at 500°C for 45 minutes to produce a GPF. The GPF thus produced had a mass of 1.6 g / in 3 Washcoat loading, 4g / ft 3 The Pd loading is 4g / ft 3 , and 133g / ft 3 The Ba loading amount was .

[0046] Catalyst B Catalyst B is prepared following a procedure similar to that for preparing Comparative Catalyst A, except that the washcoat slurry does not contain the Ba promoter. In addition, the washcoat contains Pt instead of Pd. Furthermore, the washcoat slurry contains citric acid. The coated substrate is coated with 100 g / ft 2 of 100% ethanol after the coated substrate is dried but not calcined. 3 After calcination, the GPF produced contained 1.6 g / in 3 Washcoat loading, 4g / ft 3 Pt loading of 4g / ft 3 The Rh loading is

[0047] The cold flow back pressure (BP) of fresh Catalyst B and fresh Comparative Catalyst A is shown in Table 1. The data shows that Catalyst B has a better cold flow back pressure at 600 m compared to Comparative Catalyst A. 3 / h. The BP contribution compared to the bare filter substrate is calculated as (BP of coated area - BP of bare substrate) / (BP of bare substrate). The BP contribution of Catalyst B was 16% lower than the BP contribution of Comparative Catalyst A.

[0048] [Table 1] EXAMPLES

[0049] Light-off performance and OSC test in engine bench test Catalyst B as GPF brick and comparative catalyst A were bench aged under a 6.1L engine in a 4-mode aging cycle, with the peak bed temperature of the front TWC brick being about 980° C., and then the maximum bed temperature in the GPF of the rear GPF brick during aging being about 960° C. The aging period was 200 hours, which simulates a durability test of 200,000 km in practical use.

[0050] Bench aged catalyst B and comparative catalyst A were tested separately on a gasoline engine. The light-off performance was at typical conditions with an exhaust gas flow rate of 80 kg / h. The temperature ramp rate was 30°C / min. The lambda of the Air and Fuel Ratio (AFR) was 14.45. THC, CO, NO x The conversion was calculated by comparing the feed and outlet gas compositions.

[0051] HC, CO, and NOx T for Catalyst B and Comparative Catalyst A 50 Light-off performance (T 50 The conversion rates of Catalyst B and Catalyst C are shown in Table 2. xThe results show that catalyst B gave improved light-off performance of 100%. The T50 for HC, CO, and NOx for catalyst B are 29, 39, and 33°C lower, respectively, compared to those for comparative catalyst A. Oxygen storage capacity (OSC) tests were performed on the engine bench for the bench-aged parts at test conditions of 125 kg / h flow rate and 550°C catalyst inlet temperature, lambda amplitude 6.8% with 15 seconds switching. Catalyst B exhibits slightly higher OSC compared to comparative catalyst A, as shown in Table 2.

[0052] [Table 2] EXAMPLES

[0053] Vehicle Testing Bench-aged samples of Catalyst B and Comparative Catalyst A as GPF components were each tested on a 1.5-liter engine vehicle using the Worldwide Light Duty Testing Procedure (WLTP), with the same aged TWC samples placed in a close-coupled position and the GPF components placed in an underfloor position in the aftertreatment system. The results of vehicle exhaust diluted bag data for the bench-aged components are shown in Table 3. The vehicle test results showed that compared to Comparative Catalyst A, Catalyst B reduced the emissions of THC, CO, and NO. x It gave comparable activity to the emission control catalyst.

[0054] [Table 3] EXAMPLES

[0055] Bench Lambda Sweep Test Comparative catalyst C Comparative Catalyst C was prepared in a similar manner to Comparative Catalyst A, except that the washcoat slurry contained Pt instead of Pd. The resulting GPF after calcination was 1.6 g / in3 Washcoat loading, 6g / ft 3 Pt loading: 4g / ft 3 and 133 g / ft 3 The Ba loading amount is .

[0056] Catalyst D Catalyst D was prepared following a similar procedure to Catalyst B, except that the washcoat slurry contained a different amount of Pt. The resulting GPF after calcination was 1.6 g / in 3 Washcoat loading, 6g / ft 3 Pt loading of 4g / ft 3 The Rh loading is

[0057] Catalyst D and Comparative Catalyst C were bench aged in the same 6.1 L engine for 200 hours operation in a four mode aging cycle with a peak bed temperature in the catalyst of about 960°C.

[0058] Lambda sweep tests were performed on an engine bench by adjusting the fuel / air ratio at 400° C. and a flow rate of 80 kg / h. The THC, CO and NOx conversions of bench aged Catalyst D and Comparative Catalyst C are shown in Tables 4, 5 and 6. The data show that Catalyst D gave higher conversions of THC, CO and NOx at rich conditions with lambda less than 1.

[0059] [Table 4]

[0060] [Table 5]

[0061] [Table 6] EXAMPLES

[0062] Cold Flow Back Pressure Test Comparative catalyst E Comparative Catalyst E was prepared following a procedure similar to that for preparing Comparative Catalyst A, except that the washcoat slurry contained Pt instead of Pd and the washcoat slurry did not contain the Ba promoter. The GPF produced after calcination was 1.6 g / in 3 Washcoat loading, 4g / ft 3 Pt loading of 4g / ft 3 The Rh loading is

[0063] Catalyst F Catalyst F was prepared following a similar procedure to Comparative Catalyst E, except that the washcoat slurry contained citric acid. The resulting pre-calcined GPF precursor had a 50 g / ft 3 After calcination, the GPF produced had a citric acid loading of 1.6 g / in 3 Washcoat loading, 4g / ft 3 Pt loading of 4g / ft 3 The Rh loading is

[0064] Catalyst G Catalyst G was prepared following a similar procedure to Comparative Catalyst E, except that the washcoat slurry contained citric acid. The resulting pre-calcined GPF precursor had a yield of 75 g / ft 3 After calcination, the GPF produced had a citric acid loading of 1.6 g / in 3 Washcoat loading, 4g / ft 3 Pt loading of 4g / ft 3 The Rh loading is

[0065] Catalyst H: Catalyst H was prepared following a similar procedure to Comparative Catalyst E, except that the washcoat slurry contained citric acid. The resulting pre-calcined GPF precursor had a 100 g / ft 3 After calcination, the GPF produced had a citric acid loading of 1.6 g / in 3 Washcoat loading, 4g / ft 3 Pt loading of 4g / ft3 The Rh loading is

[0066] The cold flow backpressures of calcined Catalyst H, Catalyst G, Catalyst F, and Comparative Catalyst E are shown in Table 7. The data show that Catalyst H exhibits superior cold flow backpressures at 200, 300, 400, and 600 m compared to Catalyst G, Catalyst F, and Comparative Catalyst E, respectively. 3 / h flow rate gave the lowest backpressure results. Table 7 shows that as the amount of citric acid in the washcoat slurry increases, the BP decreases.

[0067] [Table 7]

[0068] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0069] Use of the term "comprising" is intended to be interpreted as including such features but not excluding other features, and is intended to include options of features that are necessarily limited to those recited. In other words, this term also includes the limitations "consisting essentially of" (intended to mean that certain additional components may be present provided they do not materially affect the essential properties of the recited feature) and "consisting of" (intended to mean that when components are expressed as percentages by their proportions, they add up to 100%, while accounting for any unavoidable impurities, but that other features may not be included), unless the context clearly indicates otherwise.

[0070] The foregoing detailed description has been provided for purposes of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments illustrated herein will be apparent to those of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. A method for manufacturing a gasoline particulate filter (GPF), comprising: (i) forming a washcoat slurry; (ii) coating a wall flow filter substrate with the washcoat slurry to form a washcoated substrate; (iii) firing the washcoated substrate to form a GPF, wherein the washcoat slurry contains: (a) a platinum group metal (PGM) component consisting of Pt and Rh; (b) an oxygen storage capacity (OSC) material; (c) carboxylate ions, and the OSC material is ceria or a mixed oxide containing ceria.

2. The method according to claim 1, wherein the carboxylate ions are selected from the group consisting of citrate ions, malate ions, malonic acid ions, succinic acid ions, tartaric acid ions, glutaric acid ions, tartronic acid ions, oxalic acid ions, lactic acid ions, glycolic acid ions, and mixtures thereof.

3. The method according to claim 1, wherein the carboxylate ions are selected from the group consisting of citrate ions, malonic acid ions, and mixtures thereof.

4. The method according to claim 1, wherein the carboxylate ions are citrate ions.

5. The method according to claim 1, wherein the washcoat slurry contains carboxylate ions and Pt in a molar ratio of 1:1 to 100:

1.

6. The method according to claim 1, wherein the washcoat slurry contains carboxylate ions and Pt in a molar ratio of 5:1 to 50:

1.

7. The method according to claim 1, wherein the washcoat slurry contains carboxylate ions and Pt in a molar ratio of 10:1 to 25:

1.

8. The method according to claim 1, wherein the washcoat slurry is substantially free of Ba.

9. The method according to claim 1, wherein the washcoat slurry further contains an inorganic oxide carrier containing alumina.

10. The method according to claim 1, wherein the washcoat slurry is coated on the inlet channels and outlet channels of the wall flow filter substrate.

11. A pre-fired gasoline particulate filter precursor comprising a washcoated wall flow filter substrate including a washcoat, wherein the washcoat contains: (a) a platinum group metal (PGM) component consisting of Pt and Rh; (b) an oxygen storage capacity (OSC) material; (c) including carboxylic acid ions, The pre-fired gasoline particulate filter precursor, wherein the OSC material is ceria or a mixed oxide containing ceria. **Claim 12**: The pre-fired gasoline particulate filter precursor according to claim 11, wherein the carboxylic acid ions are selected from the group consisting of citrate ions, malate ions, malonic acid ions, succinic acid ions, tartaric acid ions, glutaric acid ions, tartronic acid ions, oxalic acid ions, lactic acid ions, glycolic acid ions, and mixtures thereof. **Claim 13**: The pre-fired gasoline particulate filter precursor according to claim 11, wherein the carboxylic acid ions are selected from the group consisting of citrate ions, malonic acid ions, and mixtures thereof. **Claim 14**: The pre-fired gasoline particulate filter precursor according to claim 11, wherein the carboxylic acid ions are citrate ions. **Claim 15** The pre-fired gasoline particulate filter precursor according to claim 11, wherein the washcoat contains carboxylic acid ions and Pt in a molar ratio of 1:1 to 100:

1. **Claim 16** The pre-fired gasoline particulate filter precursor according to claim 11, wherein the washcoat contains carboxylic acid ions and Pt in a molar ratio of 5:1 to 50:

1. **Claim 17** The pre-fired gasoline particulate filter precursor according to claim 11, wherein the washcoat substantially does not contain Ba. **Claim 18** The pre-fired gasoline particulate filter precursor according to claim 11, wherein the washcoat further contains an inorganic oxide carrier containing alumina. **Claim 19** A method for manufacturing a gasoline combustion and exhaust gas treatment system, comprising: (a) providing a gasoline engine having an exhaust manifold; (b) manufacturing a gasoline particulate filter according to the method described in claim 1; (c) forming an exhaust gas treatment system including the gasoline particulate filter and connecting the exhaust gas treatment system to the exhaust manifold of the gasoline engine.