Method for manufacturing a gasoline particulate filter

Abstract

A method for the manufacture of a gasoline particulate filter (GPF) for the treatment of exhaust gases is disclosed. The method includes (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 gasoline particulate filter. The washcoat slurry includes (a) a platinum group metal selected from the group consisting of Pt, Pd, Rh, and mixtures thereof, (b) an oxygen storage capacity (OSC) material, and (c) a C2-C6 aliphatic amino acid.

Description

[Technical Field]

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

[0002] Gasoline particulate filters (GPFs) are an emissions aftertreatment technology based on diesel particulate filters (DPFs) that were developed to control particulate emissions from gasoline direct injection (GDI) engines.

[0003] Most early GPF applications involved uncoated GPFs positioned downstream of a three-way catalyst (TWC). As the technology matured, GPFs were also 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 catalyst coating on the filter body introduced additional problems, such as excessive backpressure and the need for minimal CO, NO, and CO2 emissions. x , and there are requirements for HC conversion characteristics.

[0004] WO2017056067A1 discloses a catalytic wall-flow monolith filter with three-way catalytic activity for use in the emission treatment system of a positive-ignition internal combustion engine, characterized by having the amount by weight of platinum group metal per unit volume of the on-wall coating present on the channel wall surface varying continuously along its length, or by varying wall thickness.

[0005] WO 2020201953(A1) discloses a catalytic article for treating exhaust gas emissions from gasoline engines, particularly a wall-flow filter suitable for treating particulate emissions having a size of less than 23 nm, which is achieved by the use of specific particulate oxygen storage components having controlled particle sizes.

[0006] US Patent No. 10,570,063 (B1) discloses the use of beta-alanine as a dispersant in the production of nano-suspension mixed oxides. There is no suggestion in US Patent No. 10,570,063 (B1) that these may be desirably used in exhaust gas treatment applications.

[0007] WO2017178801A1 discloses a method for coating a substrate with a foam, the method comprising: (a) introducing foam into a substrate including a plurality of channels through open ends of the channels at a first end of the substrate; and (b) optionally applying (i) a vacuum to the open ends of the channels at a second end of the substrate and / or (ii) pressure to the open ends of the channels at the first end of the substrate, wherein the foam comprises a particulate material, and the foam is particle-stabilized.

[0008] It is an object of the present invention to provide an improved method for producing GPFs to address the problems associated with the prior art. Summary of the Invention

[0009] The present invention relates to a method for the manufacture of a gasoline particulate filter (GPF) for the treatment of exhaust gases, the method 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; The washcoat slurry includes (a) a platinum group metal selected from the group consisting of Pt, Pd, Rh, and mixtures thereof, (b) an oxygen storage capacity (OSC) material, and (c) a C2-C6 aliphatic amino acid. [Brief explanation of the drawings]

[0010] [Figure 1] SEM images of the anterior central portion of GPF-A (top) and GPF-B (bottom) are shown. [Figure 2] Figure 1 shows cumulative NOx during a JLR RDE drive cycle for hydrothermally aged GPF-A compared to that of hydrothermally aged GPF-C. The solid line correlates to GPF-A. The dashed line correlates to GPF-C. The grey line correlates to vehicle speed. [Figure 3] T50 light-off temperatures for CO, THC (total hydrocarbons), and NOx are shown. Solid bars correlate to GPF-A. Dashed bars correlate to GPF-C. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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 aspects / embodiments, 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.

[0012] The present invention relates to a method for the manufacture of a gasoline particulate filter (GPF) for the treatment of exhaust gases, the method 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 gasoline particulate filter; The washcoat slurry includes (a) a platinum group metal selected from the group consisting of Pt, Pd, Rh, and mixtures thereof, (b) an oxygen storage capacity (OSC) material, and (c) a C2-C6 aliphatic amino acid.

[0013] Therefore, within the scope of the present invention, a gasoline particulate filter refers to a catalyst coated wall-flow filter substrate.

[0014] A wall-flow filter substrate typically has a first face and a second face defining a longitudinal direction therebetween, and first and second pluralities of channels extending longitudinally, the first plurality of channels being open at the first face and closed at the second face, the channels of the first plurality of channels being partially defined by channel walls, the second plurality of channels being open at the second face and closed at the first face, the channels of the second plurality of channels being partially defined by channel walls, and the channel walls between the channel walls of the first and second plurality of channels being porous.

[0015] The wall-flow filter substrate can be a ceramic porous substrate such as cordierite, aluminum titanate, silicon carbide, and the like. The filter substrate can have a porosity of 40-75%, such as 45-70% or 50-60%.

[0016] The method includes forming a washcoat slurry. The washcoat slurry includes a solvent. Water is a preferred solvent for the washcoat slurry.

[0017] The washcoat slurry contains platinum group metals (PGMs) selected from the group consisting of Pt, Pd, Rh, and mixtures thereof. Preferably, the washcoat slurry contains Pt and Rh, or Pd and Rh. For example, the washcoat slurry may contain Pt and Rh. Alternatively, the washcoat slurry may contain Pd and Rh. The amount of total PGMs in the washcoat slurry may 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.

[0018] 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.

[0019] The OSC material can be ceria or a mixed oxide containing ceria. Preferably, the OSC material comprises 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. The term "mixed oxide," as used herein, generally refers to a mixture of oxides in a single phase, as conventionally known in the art. In one embodiment, the OSC material comprises a cerium-zirconium mixed oxide nanosol having an average particle size of less than 1 μm. In another embodiment, the OSC material comprises a cerium-zirconium mixed oxide having an average particle size of 1 to 20 μm, preferably 2 to 15 μm, and more preferably 5 to 10 μm.

[0020] The amount of OSC material in the washcoat slurry can be 5 to 50 wt %, preferably 10 to 30 wt %, based on the total weight of the washcoat slurry.

[0021] The washcoat slurry includes a C2-C6 aliphatic amino acid. Suitable C2-C6 aliphatic amino acids include 3-amino-propionic acid, L-alanine, glycine, serine, L-valine, and the like. Preferably, the C2-C6 aliphatic amino acid has the formula HO2C-(CH2) n An amino acid having -NH2, where n is 1 to 5, preferably 1 to 3. One preferred amino acid is 3-amino-propionic acid (n=2).

[0022] The amount of C2-C6 aliphatic amino acid in the washcoat slurry can be 1-50% by weight, preferably 2-40% by weight, more preferably 5-30% by weight, based on the crucible solid in the washcoat slurry.

[0023] The washcoat slurry may further comprise an inorganic oxide support. The inorganic oxide support may be an oxide of an element from Groups 2, 3, 4, 5, 13, or 14. The inorganic oxide support is preferably a refractory oxide that exhibits chemical and physical stability at high temperatures, such as temperatures 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. In one embodiment, the inorganic oxide support is gamma-alumina. The gamma-alumina used as the inorganic oxide support preferably has an average particle size of 1 to 10 μm, more preferably 2 to 8 μm. In another embodiment, the inorganic oxide support is nano-alumina. The nano-alumina used as the inorganic oxide support preferably has an average particle size of less than 1 μm.

[0024] The inorganic oxide support can be doped with a dopant. The dopant 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 can be 1 to 30% by weight, preferably 2 to 25% by weight, and more preferably 3 to 20% by weight.

[0025] The amount of the inorganic oxide support in the washcoat slurry can be 2 to 30% by weight, preferably 5 to 20% by weight, based on the total weight of the washcoat slurry.

[0026] The washcoat slurry typically has a solids content of 15 to 40% by weight, more preferably 20 to 35% by weight.

[0027] The method includes coating a wall-flow filter substrate with a washcoat slurry to form a washcoated substrate. The coating may be applied 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 GB Patent No. 2524662(A).

[0028] The method further includes calcining the washcoated substrate to form a GPF. Calcination can be preceded by a drying step at a lower temperature (e.g., 80-200°C). Calcination is routine in the art and can be carried out under conventional conditions.

[0029] After calcination, the PGM loading in the GPF is typically 1 g / ft 3 ~50g / ft 3 , more preferably 5 g / ft 3 ~40g / ft 3The washcoat loading on the calcined GPF is typically 0.2 g / in 3 ~5g / in 3 , more preferably 0.5 g / in 3 ~3g / in 3 is.

[0030] The inventors have found that the inclusion of C2-C6 aliphatic amino acids reduces the viscosity of the washcoat slurry. As a result, the washcoat slurry can penetrate deeper into the pores of the substrate, which has been found to reduce backpressure. In addition, the inclusion of C2-C6 aliphatic amino acids improves the catalytic performance of GPFs. [Example]

[0031] Example 1 GPF preparation Wash Coat Slurry A-1 Washcoat slurry A-1 was prepared containing Pd nitrate, Rh nitrate, cerium-zirconium mixed oxide nanosol (average particle size 390 nm), gamma-phase alumina (average particle size 5 μm), and water. The slurry had a solids content of 25% and a viscosity of >500 cP as measured at 20° C. with a Brookfield™ RV DVII+Extra Pro viscometer using an SC4-27 spindle at a spindle speed of 50 rpm.

[0032] GPF-A (comparison example) The washcoat slurry A-1 prepared above was coated from both the inlet and outlet faces of a cordierite wall-flow honeycomb filter substrate (300 cells per square inch, average pore size of 17 μm, porosity of 66%) using the coating procedure described in British Patent No. 2524662. A predetermined amount of the slurry was deposited on the top end of the filter substrate using a slurry dosing head. The dosing head had multiple openings arranged to dispense the slurry onto the top face of the filter substrate. A vacuum was applied to the bottom end of the filter substrate to draw the slurry along the channels, thereby coating the open-ended channels at the top end of the filter substrate with a predetermined amount of slurry. The coating length on the inlet channel was approximately 30% of the substrate length. The coating length on the outlet channel was approximately 70% of the substrate length. The coated substrate was dried at 110°C and calcined at 500°C to produce a GPF. The resulting GPF had a density of 1.64 g / in. 3 Washcoat loading of 35g / ft 3 Pd loading of 10g / ft 3 The Rh loading is

[0033] The SEM image of the front center section of GPF-A shows that a significant amount of washcoat is present on the wall, as shown in Figure 1(a).

[0034] Wash Coat Slurry B-1 Washcoat slurry B-1 was prepared containing Pd nitrate, Rh nitrate, a mixed ceria-zirconia mixed oxide (average particle size 7 μm), nanoalumina boehmite (average particle size 70-120 nm), and water. The washcoat slurry had a solids content of 30%. The slurry had a viscosity of >3000 cP as measured at 20°C with a Brookfield™ RV DVII+Extra Pro viscometer using an SC4-27 spindle at a spindle speed of 50 rpm.

[0035] Wash Coat Slurry B-2 Washcoat Slurry B-2 was prepared containing Pd nitrate, Rh nitrate, a mixed ceria-zirconia mixed oxide composite (average particle size 7 μm), nano-alumina boehmite (average particle size 70-120 nm), 3-aminopropanoic acid, and water. The amount of 3-aminopropanoic acid was 40 wt % based on the crucible solids in the washcoat slurry. Washcoat Slurry B-2 had a solids content of 30%. The slurry had a viscosity of <50 cP as measured at 20°C with a Brookfield™ RV DVII+Extra Pro viscometer using an SC4-27 spindle at a spindle speed of 50 rpm. The inclusion of 3-aminopropanoic acid significantly reduced the viscosity of the slurry.

[0036] GPF-B GPF-B was prepared according to the same procedure as for the preparation of GPF-A, except that washcoat slurry B-2 was used. The resulting GPF-B had a viscosity of 1.64 g / in 3 Washcoat loading of 35g / ft 3 Pd loading of 10g / ft 3 The Rh loading is

[0037] SEM images of the anterior central section of GPF-B showed that the washcoat was mainly intramural, as shown in Figure 1(b).

[0038] GPF-C GPF-C was prepared in a manner similar to GPF B, except that the amount of 3-aminopropanoic acid was 6 wt. % relative to the crucible solids in the washcoat slurry. The washcoat slurry had a viscosity of <100 cP as measured at 20°C with a Brookfield™ RV DVII+Extra Pro viscometer using an SC4-27 spindle at a spindle speed of 50 rpm. The resulting GPF-C had a viscosity of 1.64 g / in. 3 Washcoat loading of 35g / ft 3 Pd loading of 10g / ft 3 The Rh loading was .

[0039] Example 2 Cold Flow Back Pressure Test The cold flow back pressure (BP) of fresh GPF-C and fresh GPF-A (comparative example) is shown in Table 1. The data show that when the amount of 3-aminopropanoic acid used is 6 wt% of the crucible solids in the washcoat slurry, the cold flow back pressure is reduced.

[0040] [Table 1]

[0041] Example 3. Performance test GPF-C and GPF-A were hydrothermally aged under lean conditions. They were then evaluated on an engine for three-way performance via a JLR RDE drive cycle evaluation. As shown in Figure 2, a 53% reduction in total NOx over GPF-C was measured compared to a 34% reduction in total NOx over GPF-A. Furthermore, as shown in Figure 3, GPF-C provided a 40-50°C light-off benefit in NOx, CO, and THC T50 when compared to GPF-A.

Claims

1. 1. A method for the manufacture of a gasoline particulate filter (GPF) for the treatment of exhaust gases, said method 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 gasoline particulate filter; The washcoat slurry comprises: (a) a platinum group metal selected from the group consisting of Pt, Pd, Rh, and mixtures thereof; (b) an oxygen storage capacity (OSC) material; and (c) C ２ ~C ６ an aliphatic amino acid, Said C ２ ~C ６ The aliphatic amino acid is of the formula HO ２ C-(CH ２ ) ｎ -NH ２ wherein n is 1 to 5.

2. 2. The method of claim 1, wherein n is 1 to 3.

3. 2. The method of claim 1, wherein n is 2.

4. The method of claim 1 , wherein the washcoat slurry comprises Pt and Rh.

5. The method of claim 1 , wherein the washcoat slurry comprises Pd and Rh.

6. 10. The method of claim 1, wherein the OSC material comprises 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.

7. 10. The method of claim 1, wherein the OSC material comprises a cerium-zirconium mixed oxide nanosol having an average particle size of less than 1 μm.

8. The method of claim 1 , wherein the washcoat slurry further comprises an inorganic oxide support.

Images