DE102010055147A1 - Four-way catalyst for cleaning exhaust gas of temporarily stoichiometric fueled internal combustion engine, particularly petrol engine, of vehicle, has ceramic support body, which is provided with particle filter function - Google Patents

Abstract

The four-way catalyst (10) has a ceramic support body (12), which is provided with a particle filter function for retention of carbonaceous particles. A wash coat coating (18) is arranged on a partial region of the ceramic support body. Two sections (22,24) are provided, which are different from each other in characteristic of the wash coat coating.

Description

The invention relates to a four-way catalyst for at least temporarily stoichiometric (lambda = 1) operated internal combustion engines, in particular gasoline engines, a use of the four-way catalyst and a vehicle having such.

Equipping diesel-fueled vehicles with particulate filters to reduce carbonaceous particulate emissions is today's practice and is required by law in many countries. In addition, there are also approaches in the diesel engine sector to combine the particle retention function and catalytic functions in common components.

EP 1 837 495 A1 describes a combined exhaust aftertreatment system for a lean burn internal combustion engine having an oxidation catalyst for converting carbon monoxide CO and unburned hydrocarbons HC, a NO _x storage catalyst for storing and reducing nitrogen oxides NO _x, and a particulate filter for collecting and burning soot particles. The oxidation catalyst, the NO _x storage catalyst and the particulate filter are connected in series in this order and in particular may be arranged on a common carrier substrate.

Out DE 10 2008 037 156 A1 is a catalyst for lean-running internal combustion engines, in particular diesel engines, known which has a particulate filter function and various catalytically active components, on the one hand convert carbon monoxide CO and HC hydrocarbons in lean operation and on the other hand convert nitrogen oxides NO _x to ammonia NH ₃ in rich operation. The latter is used in a downstream of the four-way catalyst SCR catalyst as a reducing agent for NO _x conversion in lean operation.

Unlike diesel engines, however, only gaseous exhaust components are currently legally limited in gasoline engines. Thus, gasoline engines that are operated continuously or at least temporarily with a stoichiometric air-fuel mixture, usually only equipped with a catalytic converter with a three-way catalytic coating, which on the one hand the exhaust components carbon monoxide (CO) and unburned hydrocarbons (HC) Carbon dioxide (CO ₂ ) and water (H ₂ O) oxidize and on the other hand reduces nitrogen oxides (NO _x ) to nitrogen (N ₂ ).

The desire for a further reduction of emissions as well as future expected exhaust emission limits, for example in Europe and in the USA, lead to the requirement to lower particulate matter (PM) and particulate matter (PA) emissions for gasoline engines as well. All limit values should be adhered to for at least a defined vehicle life. This may require the use of particulate filters for gasoline engines as well.

It would be desirable to have a catalytic converter concept for gasoline engines in which a three-way catalyst with a particle retention function is realized in a single catalyst with a common carrier body (four-way catalyst). As a carrier for catalysts, as well as for particulate filter, ceramic substrates are used. Known catalyst carriers for the Otto engine sector have much higher cell densities and much lower carrier wall thicknesses in comparison to known diesel particle filters due to the strict exhaust gas limit values. However, due to production reasons, the cell density for particle filters can not be increased arbitrarily and due to the strength of the wall thicknesses can not be reduced arbitrarily. Due to the associated comparatively large heat capacity of the carrier takes place after a cold start necessary for the catalytic activity heating only slowly and the critical light-off temperature is reached late, which has a negative effect on the cold-start emissions. To make matters worse by the catalytic coating, in particular the so-called washcoat coating, caused increased wall thickness and heat capacity added. These reasons have hitherto prevented practice-relevant concepts for a so-called four-way catalytic converter for gasoline engines.

The invention is therefore based on the object, a four-way catalyst for at least temporarily stoichiometric combustion engines, in particular for gasoline engines, to propose. Ideally, the four-way catalyst should allow a sufficiently rapid heating and thus a rapid achievement of the light-off temperature.

These objects are achieved by a catalytic converter, its use and a vehicle having the features of the independent claims.

The four-way catalyst according to the present invention comprises a ceramic carrier body having a particulate filter function for retaining carbonaceous particles; at least one arranged on at least a portion of the ceramic support body washcoat coating which at least partially has at least one oxygen-storing component; and at least one catalytically active component supported on at least a portion of the washcoat coating, which is suitable Under an at least approximately stoichiometric exhaust gas atmosphere hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) catalytic convert. According to the invention, the catalyst has at least two sections which differ from each other at least in their washcoat coating.

The inhomogeneous according to the invention with respect to an inner surface of the carrier body washcoat coating is made possible to select the washcoat properties so that an early light-off of the catalyst is ensured and thus the cold start emissions are reduced. Unlike in the "zone coating" known in the prior art, in which a carrier body has a homogeneous washcoat coating over the entire carrier body, but zones with different noble metals, the zones of the inventive catalyst differ in their washcoat coating, in particular a surface-related washcoat mass (or washcoat thickness), a chemical washcoat composition, a type of oxygen-storing component and / or a mass per unit area of the oxygen-storing component. In other words, the washcoat coating may vary in its chemical composition with respect to the washcoat base substance and / or the oxygen-storing component and / or in the surface-related amounts of the washcoat base substance and / or the oxygen-storing component.

In a preferred embodiment, it is provided that a first, upstream portion of the catalyst has a lower area-related washcoat mass than a second portion of the catalyst that is downstream relative to the first portion with respect to a flow path of the exhaust gas within the catalyst. Due to the relatively low mass of the washcoat in the first, upstream section, a comparatively low heat capacity is achieved in this area, which after a cold start leads to a rapid heating of the section and thus to a rapid start-up of the upstream section. Once the first section has been heated, due to the exothermic nature of the catalytic reactions of the gaseous exhaust gas components, rapid further heating in this section and the high exhaust gas temperatures also occur in the subsequent section (s).

In a further advantageous embodiment, a first, upstream section of the catalyst has a lower surface-related mass of the oxygen-storing component and / or an oxygen-storing component of lower oxygen storage capability than a second, downstream section of the catalyst. In this way, the first portion has a comparatively low or even no oxygen storage capacity (OSC), so that the oxygen contained in the exhaust gas is not stored and flows into further separated regions of the catalyst, where it is available for the oxidation of deposited particles. In oxygen-rich operating points of the engine, a regeneration of the catalyst thus takes place without separate fuel-consuming engine measures for particle regeneration having to be taken. With a suitable design of the coatings, a continuously regenerating catalyst is made possible.

On the one hand, the four-way catalyst according to the invention permits the reduction of carbonaceous particles, in particular of soot particles, and on the other hand has the function of a three-way catalyst by oxidizing carbon monoxide and hydrocarbons to carbon dioxide and water and reducing nitrogen oxides to nitrogen. For this purpose, the catalytically active component may comprise the noble metals platinum, palladium and / or rhodium, with the combination of platinum and rhodium or the combination of palladium and rhodium in particular being preferred.

In addition to the zone-by-zone variation of the washcoat coating, the at least two sections may also differ in their composition of the catalytically active component and / or in a surface-related mass of the catalytically active component. For example, a higher mass (loading) with the catalytically active component can be provided in a downstream section in order to generate high temperatures in these areas and to assist the (continuous) particle burnup.

According to a further preferred embodiment, the ceramic carrier body has a so-called wall-flow filter structure. In such a particle filter architecture, part of the flow channels present in the substrate are closed on the inlet side (outlet channels) and the other part open on the inlet side (inlet channels). In this way, the exhaust gas flowing into an inlet channel is forced to flow from an inflow surface of the inlet channel through the ceramic wall, in order to pass via an outflow surface of the wall into an outlet channel. By passing a wall at least once a very high filter efficiency is achieved.

In particular, in the above-described wall-flow filter structure, it is possible that the differently coated portions are arranged not only in the axial direction to each other, that is in the main flow direction of the exhaust gas, but also in the radial direction, that is transverse to Main flow direction. For example, the inlet channels, that is to say the inflow surfaces, may have a different washcoat than the outlet channels, that is to say the outflow surfaces. In other words, the catalyst can have varying coatings along its longitudinal section and / or along its cross section, whereby a large number of options for adapting the coating characteristics to the local requirements exists and the catalyst can be optimally designed.

Another aspect of the present invention relates to the use of the four-way catalyst described above for purifying an exhaust gas of an at least temporarily stoichiometric combustion engine, in particular a gasoline engine.

Yet another aspect of the present invention relates to a vehicle having an at least temporarily stoichiometric combustion engine and an exhaust system connected thereto, which contains a four-way catalyst according to the invention. Here, on the one hand, a single-catalyst concept can be realized, in which the four-way catalyst is contained as a single catalyst, preferably at a mounting position close to the engine. In an alternative embodiment, the four-way catalyst is part of a Mehrkatalysatorkonzepts, in which the four-way catalyst according to the present invention is preceded by a precatalyst, which may be configured in particular as a three-way catalyst. In this concept is the. Four-way catalyst preferably provided on an underbody mounting position. In a further embodiment of a multi-catalyst concept, the four-way catalyst according to the invention is arranged at a position close to the engine and thus fulfills the function of a fast-starting precatalyst and a conventional three-way catalyst is in an underfloor installation position.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

1 schematically a four-way catalyst according to the present invention in a longitudinal sectional view;

2 an internal combustion engine with exhaust system with a single catalytic converter concept,

3 an internal combustion engine with exhaust system with a dual catalytic converter according to a first embodiment and

4 an internal combustion engine with exhaust system with a dual catalytic converter according to a second embodiment.

1 shows a section of a total with 10 designated four-way catalyst according to the present invention in a greatly enlarged view in longitudinal section of the catalyst. In the upper part of the figure, a further enlargement of a detail is shown.

The catalyst 10 has a ceramic porous carrier body 12 on, for example, made of the material cordierite, silicon carbide, aluminum titanate or the like is preferably made in one piece. The carrier body is preferably designed as a so-called wall-flow filter. This means that part of the parallel flow channels, namely the inlet channels 14 , opened on the input side and closed on the output side. The other part of the flow channels, the outlet channels 16 on the other hand, the input side is closed and the output side is open. In a preferred embodiment, the inlet channels change 14 and exit channels 16 from. One in the entrance channels 14 the exhaust gas flowing in from the catalytic converter (see horizontal arrows) is thus forced to flow through the lateral walls in order to enter the outlet channels 16 to get to and from there the catalyst 10 to leave. When passing through the ceramic walls particulate constituents of the exhaust gas, in particular carbonaceous particles are retained and deposited on the surface but also in deeper layers of the ceramic material. The carrier body 12 typically has a cell density in the range of 150 to 500 cpsi (cells per square inch), especially in the range of 200 to 400 cpsi, with a wall thickness in the range of 5 to 12 mils (equivalent to 1/1000 inch (= 25.4 μm)), in particular from 8 to 10 mil.

An inner surface of the carrier body 12 that is the flow channels 14 . 16 , Has at least partially a washcoat coating 18 on. This is a porous, surface-increasing material, typically a metal oxide, such as alumina Al ₂ O ₃ . In addition, an oxygen-storing material that reversibly binds the molecular oxygen in an oxygen-containing exhaust gas atmosphere may be added to this base material. For example, metal oxides such as cerium (IV) oxide CeO ₂ and / or zirconium (IV) oxide ZrO ₂ can be used as oxygen-storing materials.

On an outer and partially inner surface of the washcoat coating 18 there is at least one catalytically active component 20 , which is suitable, the exhaust components unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) at least under an at least approximately stoichiometric exhaust gas atmosphere to convert catalytically into carbon dioxide (CO ₂ ), water (H ₂ O) and molecular nitrogen (N ₂ ). For this purpose, in particular noble metals are used, wherein platinum (Pt) and / or palladium (Pd) catalyze the reaction of HC and CO and rhodium (Rh) the reaction of NO _x . For example, a combination of Pt and Rh or of Pd and Rh can be used.

The catalytically active component 20 is supported in the finest possible particulate distribution on the washcoat in order to provide the largest possible catalytic surface.

Due to the catalytic coating, the catalyst 10 on the one hand, a three-way catalytic function on and by the particle retention function, in particular in the form of the wall-flow filter structure, a particle filter function, so that the catalyst 10 can be referred to as a four-way catalyst.

The four-way catalyst according to the invention 10 now has at least two or more sections, resulting in at least one property of the washcoat coating 18 differ from each other. In particular, the sections may be in the washcoat mass or the layer thickness of the washcoat coating 18 differ based on the carrier body surface and / or in the chemical washcoat composition, that is, the washcoat base material. Furthermore, the sections may differ in the nature of the oxygen storage component and / or a mass per unit area of the oxygen storage component. The properties of the washcoat in the various sections are preferably selected on the one hand such that the catalyst 10 achieved its light-off temperature as quickly as possible after a cold engine start, and on the other hand, that the four-way catalyst 10 Regarding the deposited particles as far as possible continuously regenerated.

In the in 1 illustrated embodiment, the catalyst 10 a first section 22 in particular arranged upstream (input side) with respect to an in-catalyst flow. In particular, the first section is located in the illustrated example 22 in an inflow-side region of the inlet channels 14 , A second section 24 is in a respect to the first section 22 downstream region of the catalyst 10 , Especially in areas of the inlet channels 14 downstream of the first section 22 as well as in the outlet channels 16 ,

In an advantageous embodiment, the first, upstream section 22 a lower area-based washcoat mass than the second, downstream section 24 , This can be achieved by a smaller layer thickness of the washcoat coating 18 of the first section 24 be achieved. In this way, a lower heat capacity of the first section 22 achieved. At the same time it is envisaged that the first section 22 over a sufficient concentration of the catalytically active component (s) 20 features. Due to the low heat capacity is a rapid warming of the front section after a cold start by the hot exhaust gas 22 achieved. Once the catalytically active component 20 makes a certain conversion conversion, the further heating of the front section is due to the exothermic nature of the catalyzed reactions 22 accelerated and also the one or more subsequent sections 24 heated. Thus, the starting emissions and thus the total emissions of gaseous pollutants of a driving cycle are reduced. The first paragraph 22 can be functionally understood as a conventional precatalyst (starting catalyst).

In addition, the first, upstream section 22 have a lower mass per unit area of the oxygen storage component and / or an oxygen storage component of lower oxygen storage capacity than the second, downstream portion 24 , A lower area-related mass of the oxygen storage component can in a simple embodiment already by the lower washcoat mass in the front section 22 be realized or by a deliberately low admixture of the oxygen storage component in the washcoat base material. As a result of the measures mentioned, a comparatively low oxygen storage capacity (OSC) is provided in the first section 22 reached. This causes the exhaust with the inlet channels 14 inflowing oxygen not or only slightly in the front section 22 but directly into downstream areas of the catalyst 10 , in particular the second section 24 , flows. There he comes with deposited particles, in particular carbonaceous particles in contact and ensures sufficient exhaust gas or catalyst temperatures for a spontaneous and continuous burning of the particles.

In the second section 24 is a conventional washcoat coating 18 before, as is common in conventional three-way catalysts. In particular, the washcoat coating exhibits 18 a comparatively high OSC and a three-way functionality, which should be adapted to the entire driving cycle.

The two sections 22 and 24 Accordingly, they differ in the washcoat composition, their OSC and their ability to regenerate, and they may also have differences in their precious metals. Thus, different precious metals on the upstream side of the inlet channels 14 and the downstream side of the outlet channels may be provided, for example, only Pt and / or Pd on the downstream side and only Rh on the downstream side.

The length and distribution of the sections 22 . 24 may vary by concept. The Washcaot coating of the first section described above 22 as dargstellt only in the front region of the inlet channels 14 be provided or in addition in the front region of the discharge channels 16 (in 1 on the left side, not shown).

The 2 . 3 and 4 show three preferred uses of a four-way catalyst 10 of the present invention in a vehicle, not shown per se, by an at least temporarily stoichiometric, that is, with an air-fuel mixture with lambda = 1 operated internal combustion engine 26 is driven, in particular by a spark ignited gasoline engine. One of the internal combustion engine 26 produced exhaust gas is in an exhaust system 28 passed, in which at a position close to the engine, a lambda probe 30 is arranged, which measures the oxygen content of the exhaust gas and a, the lambda value corresponding signal λ transmitted to an unillustrated engine control unit, which in a known manner the lambda control of the engine 26 performs.

In 2 is a one-catalyst concept realized in which the inventive four-way catalyst 10 is provided as the sole catalyst. In this case, it is preferably arranged at a position close to the engine, in order to ensure particularly quick starting after a cold start. Its catalytic coating should be designed so that a sufficient conversion of the gaseous exhaust gas components HC, CO and NO _x over the entire driving cycle is ensured.

3 shows a two-catalyst concept in which the four-way catalyst 10 of the present invention is arranged at a position remote from the engine, in particular at an underfloor position of the vehicle. In this case, the four-way catalyst 10 a comparatively small volume precatalyst 32 upstream of a mounting position close to the engine, which is preferably designed as a three-way catalyst and is responsible for the conversion of the starting emissions. As the precatalyst 32 already takes over part of the pollutant conversion, the four-way catalyst 10 have a demand-adapted catalytic coating. For example, it may predominantly have rhodium for conversion of NO _x and comparatively small amounts of palladium or platinum. Moreover, in this concept, the four-way catalyst 10 , especially the first section 22 , have an adsorber component for HC and / or NO _x .

In 4 is the four-way catalyst according to the invention 10 arranged at a position close to the engine and has a comparatively small volume. By quickly reaching its operating temperature, it acts as a starting catalyst and reduces primarily the starting emissions after a cold start. Downstream of the four-way catalyst 10 is a conventional three-way catalyst 34 arranged, which takes over the main conversion performance of the gaseous exhaust gas components.

LIST OF REFERENCE NUMBERS

10

Four-way catalyst

12

ceramic carrier body

14

inlet channel

16

outlet channel

18

Washcoat

20

catalytically active component

22

upstream section

24

downstream section

26

internal combustion engine

28

exhaust system

30

lambda probe

32

precatalyzer

34

Three-way catalytic converter

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1837495 A1 [0003]
• DE 102008037156 A1 [0004]

Claims (13)

Four-way catalyst ( 10 ) comprising a ceramic carrier body ( 12 ) having a particulate filter function for retaining carbonaceous particles; at least one on at least a portion of the ceramic carrier body ( 12 ) Washcoat coating ( 14 ), which at least partially has at least one oxygen storage component; and at least one on at least a portion of the washcoat coating ( 18 ) supported catalytically active component ( 20 ) for the catalytic conversion of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) under an at least approximately stoichiometric exhaust gas atmosphere, characterized in that the catalyst ( 10 ) at least two sections ( 22 . 24 ), which in at least one property of the washcoat coating ( 18 ) differ from each other. Four-way catalyst according to claim 1, characterized in that the at least two sections ( 22 . 24 ) in a surface-based washcoat composition, a washcoat composition, a type of oxygen storage component, and / or a basis weight of the oxygen storage component. Four-way catalytic converter according to claim 2, characterized in that a first, upstream portion ( 22 ) of the catalyst ( 10 ) has a lower area-related washcoat mass than a second, downstream portion ( 24 ) of the catalyst ( 10 ). Four-way catalyst according to claim 2 or 3, characterized in that a first, upstream section ( 22 ) of the catalyst ( 10 ) has a lower mass per unit area of the oxygen storage component and / or an oxygen storage component of lower oxygen storage capacity than a second, downstream portion (FIG. 24 ) of the catalyst ( 10 ). Four-way catalyst according to one of the preceding claims, characterized in that the at least two sections ( 22 . 24 ) additionally in their composition of the catalytically active component ( 20 ) and / or in a basis-weighted mass of the catalytically active component ( 20 ) differ from each other. Four-way catalyst according to one of the preceding claims, characterized in that the at least one catalytically active component ( 20 ) the noble metals platinum, palladium and / or rhodium, in particular platinum and rhodium or palladium and rhodium. Four-way catalyst according to one of the preceding claims, characterized in that the ceramic carrier body ( 12 ) has a wall-flow filter structure. Four-way catalyst according to one of the preceding claims, characterized in that the at least two sections ( 22 . 24 ) different washcoat coating ( 18 ) are arranged to each other in the radial direction and / or in the axial direction with respect to a main flow direction. Four-way catalyst according to one of the preceding claims, characterized in that the ceramic carrier body ( 12 ) has a cell density in the range of 150 to 500 cpsi, in particular in the range of 200 to 400 cpsi. Use of a four-way catalyst ( 10 ) according to one of claims 1 to 9 for the purification of an exhaust gas of an at least temporarily stoichiometrically operated internal combustion engine ( 26 ), in particular a gasoline engine. Vehicle with an at least temporarily stoichiometric combustion engine ( 26 ) and a connected exhaust system ( 28 ), which is a four-way catalyst ( 10 ) according to one of claims 1 to 9. Vehicle according to claim 11, characterized in that the exhaust system ( 28 ) the four-way catalyst ( 10 ) contains as a single catalyst, in particular at a mounting position close to the engine. Vehicle according to claim 11, characterized in that the exhaust system ( 28 ) a precatalyst ( 32 ), in particular a three-way catalyst, as well as the pre-catalyst ( 32 ) downstream four-way catalyst ( 10 ), in particular on a subfloor installation position.

Images