Catalytic article and the use thereof for the treatment of an exhaust gas

Abstract

A close-coupled catalytic article, and its use in an exhaust system for internal combustion engines, is disclosed. The close-coupled catalytic article for the treatment of an exhaust gas comprising: an upstream substrate and a downstream substrate, wherein the upstream substrate is spaced apart from the downstream substrate, wherein the upstream substrate comprises a first three-way catalyst (TWC) composition and the downstream substrate comprises a second TWC composition, the first and second TWC compositions each comprising an oxygen storage component (OSC), wherein a loading of the OSC in the downstream substrate is greater than a loading of the OSC in the upstream substrate and is at least 2.2 g/in.sup.3.

Claims

1. A close-coupled catalytic article for the treatment of an exhaust gas, the article comprising an upstream substrate and a downstream substrate, wherein the upstream substrate is spaced apart from the downstream substrate, wherein the upstream substrate comprises a first three-way catalyst (TWC) composition and the downstream substrate comprises a second TWC composition, the first and second TWC compositions each comprising an oxygen storage component (OSC), wherein a loading of the OSC in the downstream substrate is greater than a loading of the OSC in the upstream substrate and is at least 2.2 g/in.sup.3.

2. The close-coupled catalytic article according to claim 1, wherein the loading of the OSC in the downstream substrate is from 2.2 to 4 g/in.sup.3, preferably from 2.4 to 2.6 g/in.sup.3 and most preferably about 2.5 g/in.sup.3.

3. The close-coupled catalytic article according to claim 1, wherein the loading of the OSC in the upstream substrate is from 0.5 to 2 g/in.sup.3, preferably from 1 to 1.5 g/in.sup.3 and most preferably about 1.3 g/in.sup.3.

4. The close-coupled catalytic article according to claim 1, wherein the loading of the OSC in the upstream substrate is at least 0.4 g/in.sup.3 lower than the loading in the downstream substrate.

5. The close-coupled catalytic article according to claim 1, wherein the upstream substrate is spaced apart from the downstream substrate by from 1 to 5 cm, preferably from 2 to 3 cm.

6. The close-coupled catalytic article according to claim 1, wherein a ratio of a volume of the upstream substrate to a volume of the downstream substrate is from 2:1 to 1:2, preferably 1.5:1 to 1:1.5, more preferably about 1:1.

7. The close-coupled catalytic article according to claim 1 wherein the total content of OSC in the downstream substrate is greater than the total content of OSC in the upstream substrate.

8. The close-coupled catalytic article according to claim 1, wherein the first and/or the second TWC compositions each comprise one or more platinum group metals selected from Pd, Pt and Rh on a support, preferably wherein the first and/or second TWC compositions comprise Pd and Rh provided in separate layers.

9. The close-coupled catalytic article according to claim 8, wherein the support for the platinum group metals is independently selected from the group consisting of alumina, silica-alumina, alumino-silicates, alumina-zirconia, alumina-ceria and alumina-lanthanum.

10. The close-coupled catalytic article according to claim 1, wherein the OSC of the first and second TWCs each independently comprise ceria or a cerium-containing mixed oxide.

11. The close-coupled catalytic article according to claim 1, wherein the OSC of the first and second TWCs each independently are selected from the group consisting of cerium oxide, a ceria-zirconia mixed oxide, and an alumina-ceria-zirconia mixed oxide.

12. The close-coupled catalytic article according to claim 10 wherein the total cerium content in the downstream substrate is greater than the total cerium content in the upstream substrate.

13. The close-coupled catalytic article according to claim 12 wherein the total cerium content in the downstream substrate is at least 35% greater than the total cerium content in the upstream substrate, preferably at least 40% greater, more preferably at least 45% greater.

14. The close-coupled catalytic article according to claim 1, wherein first and or second substrates are each a flow-through monolith, preferably comprising cordierite, cordierite- alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, -alumina, or an aluminosilicate.

15. The close-coupled catalytic article according to claim 1, provided in a single can or housing.

16. An exhaust gas treatment system comprising the close-coupled catalytic article according to claim 1.

17. The exhaust gas treatment system according to claim 16 and further comprising first and second oxygen sensors arranged to monitor oxygen levels across the upstream substrate.

18. A gasoline engine comprising the exhaust gas treatment system according to claim 16.

19. A method of treating an exhaust gas from an internal combustion engine comprising the exhaust gas treatment system according to claim 17 and further comprising means to adjust an air-to-fuel ratio within the engine, the method comprising: monitoring oxygen levels across the upstream substrate and adjusting the air-to-fuel ratio in response to changes in the monitored oxygen levels.

Description

[0046] The invention will now be described in relation to the following non-limiting figures, in which:

[0047] FIG. 1 shows a catalytic article as described herein.

[0048] FIG. 2 shows an exhaust treatment system comprising the catalytic article described herein and an engine.

[0049] FIG. 1 shows a catalyst article 1 comprising a housing 5 which forms part of an exhaust gas treatment system. The housing 5 contains an upstream brick 10 and a downstream brick 15 (also referred to as upstream and downstream substrates herein). The housing 5 is generally cylindrical and the upstream and downstream bricks 10, 15 are correspondingly shaped so as to fill the housing 5. The housing 5 has an inlet 6 for receiving an exhaust gas from a combustion engine (not shown in FIG. 1). The housing 5 has an outlet 7 for the treated exhaust gas passing onwards in the exhaust gas treatment system (such as to a hydrocarbon trap).

[0050] The upstream and downstream bricks 10, 15 are monolithic honeycomb flow-through substrates made of cordierite. The upstream brick 10 has a generally flat circular upstream-facing face 20 and a generally flat circular downstream-facing face 25. The downstream brick 15 has a generally flat circular upstream-facing face 30 and a generally flat circular downstream-facing face 35. The downstream-facing face 25 of the upstream brick 10 is spaced from the upstream-facing face 35 of the downstream brick by a spacing X.

[0051] The upstream brick 10 comprises a TWC composition. For example, the composition comprises Pd, Rh, alumina and an SC component. The downstream brick 15 also comprises a TWC composition. For example, the composition comprises Pd, Rh, alumina and an OSC component. The loading of the OSC component in the upstream brick 10 is less than the loading in the downstream brick 15.

[0052] The spacing X is about 2-3 cm. Since the downstream-facing face 25 of the upstream brick 10 and the upstream-facing face 30 are substantially parallel, the spacing X is substantially constant.

[0053] The catalyst article 1 comprises a first oxygen sensor 40 and a second oxygen sensor 45. The first oxygen sensor 40 is located upstream of the upstream brick 10. Although the first oxygen sensor 40 has been shown as part of the housing 5, it could also be provided separately upstream. The second oxygen sensor 45 is located upstream of the downstream brick 15 and downstream of the upstream brick 10.

[0054] The oxygen sensors 40, 45 are standard devices and work to determine the level of oxygen is present in the gas presented to the sensor. Therefore the sensors 40, 45 require access to the gases flowing through the housing 5. The sensor may be remote from the housing 5, provided they can be used to measure the associated gases. The spacing X serves to provide a region of the exhaust gases between the upstream brick 10 and the downstream brick 15 on which the oxygen measurement can be performed.

[0055] FIG. 2 shows an internal combustion engine 50 in gaseous communication with the catalyst article 1. The catalyst article 1 is further in gaseous communication with the remainder 55 of the exhaust gas treatment system 8, which comprises at least an outlet to the environment, but can also comprise other catalyst articles (such as gasoline particulate filter, a hydrocarbon trap and/or an SCR catalyst).

[0056] In use, an exhaust gas from a combustion engine 50 exits the engine 50 and flows to the catalyst article 1, passing the first oxygen sensor 40 on the way. The first oxygen sensor 40 monitors the level of oxygen and relays this information to a controller of the air/fuel ratio in the engine 50.

[0057] The exhaust gas then contacts the upstream brick 10 where the TWC catalyst treats at least a portion of the exhaust gas. The exhaust gas then leaves the upstream brick 10 and enters the spacing X between the upstream and downstream bricks 10, 15. The second oxygen sensor 45 monitors the level of oxygen and passes this information to a controller of the air/fuel ratio in the engine 50.

[0058] The exhaust gas then passes to the downstream brick 15 where the TWC catalyst treats at least a portion of the exhaust gas. The exhaust gas then leaves the downstream brick 15, out of the outlet 7 and enters the remainder of the exhaust gas treatment system 55

[0059] The controller manipulates the air/fuel ratio based on the oxygen level data obtained from the oxygen sensors 40, 45. Based on the information provided, the air/fuel ratio can be dynamically controlled in the engine to address undesirably lean or rich conditions. The presence of the downstream brick 15 after the second oxygen sensor 45 allows catalyst article 1 to smooth out any rich or lean peaks while the air/fuel ratio is being adjusted.

[0060] The fuel injection control required to operate positive ignition engines is obtained through highly pressurised common rail fuel injections systems and the engines are referred to as gasoline Direct Injection (GDI) engines, alternatively spark ignition direct injection (SIDI) or Fuel Stratified Injection (FSI).

EXAMPLES

[0061] The invention will now be described in relation to the following non-limiting examples.

[0062] Three catalyst articles (Examples 1 to 3) were tested for their performance in treating an exhaust gas from a gasoline engine. The articles each were provided with two catalytic bricks washcoated with TWC catalysts. The bricks were made of cordierite and had the same size and porosity. In each catalyst article, the space between the two bricks was 1 inch (25.4 mm).

[0063] The upstream catalytic bricks were identical in each of the three catalyst articles. In each example, the upstream brick was washcoated with a three-way (PdRh) catalyst with CeZr mixed oxide as the OSC, wherein Pd and Rh were provided in separate layers. Each upstream brick had a total washcoat loading, total OSC loading and total cerium loading of 2.75 g/in.sup.3, 1.3 g/in.sup.3 and 750 g/ft.sup.3 respectively and the PGM ratio (Pt:Pd:Rh) was 0:63:6.5 g/ft.sup.3.

[0064] The downstream bricks were each washcoated with a three-way (PdRh) catalyst with CeZr mixed oxide as the OSC, wherein Pd and Rh were provided in separate layers, with a PGM ratio (Pt:Pd:Rh) of 0:27:6.5 g/ft.sup.3. However, the OSC loading in the downstream brick was changed in each example.

[0065] In Example 1 (comparative), the downstream brick had a total washcoat loading, a total OSC loading and a total cerium loading of 2.75 g/in.sup.3, 1.3 g/in.sup.3 and 750 g/ft.sup.3 respectively.

[0066] In Example 2 (comparative), the downstream brick had a total washcoat loading, a total OSC loading and a total cerium loading of 3.23 g/in.sup.3, 1.8 g/in.sup.3 and 1100 g/ft.sup.3 respectively.

[0067] In Example 3 (inventive), the downstream brick had a total washcoat loading, a total OSC loading and a total cerium loading of 3.93 g/in.sup.3, 2.5g/in.sup.3 and 1400 g/ft.sup.3 respectively.

[0068] The catalyst articles (Examples 1 to 3) underwent an accelerated aging to an equivalent of 150000 miles. Once aged, the catalyst articles were tested using a 2018 1.5L GTDI SULEV30 compliant passenger car under the Federal Test Procedure (FTP).

[0069] The oxygen levels were measured across the upstream brick in each case and used to control the air to fuel ratio. The levels of NOx, non-methane hydrocarbons (NMHC) and CO leaving the downstream brick were measured during the treatment process.

Analysis

[0070]

TABLE-US-00001 FTP testing NMHC NOx NMHC & NOx CO Example (g/mile) (g/mile) (g/mile) (g/mile) 1 (comparative) 0.017 0.006 0.023 0.57 2 (comparative) 0.013 0.011 0.024 0.53 3 (inventive) 0.012 0.006 0.018 0.42

[0071] As shown in the above results, NMHC+NOx and CO emissions can be reduced by more than 20% with a rear catalyst having high OSC levels. This serves to address a slow NF ratio feedback loop which would otherwise result in lean/rich spikes passing into the rear brick with excess NOx or HC/CO.

[0072] Unless otherwise stated, all percentages herein are by weight.

[0073] Although preferred embodiments of the invention have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the scope of the invention or of the appended claims.