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EP-4365421-B1 - CATALYTICALLY ACTIVE PARTICULATE FILTER

EP4365421B1EP 4365421 B1EP4365421 B1EP 4365421B1EP-4365421-B1

Inventors

  • SCHOENHABER, JAN
  • DEIBEL, Naina
  • ROESCH, MARTIN
  • SPIESS, Stephanie
  • GOTTHARDT, Meike Antonia
  • SCHICHTEL, Nicole

Dates

Publication Date
20260513
Application Date
20181214

Claims (15)

  1. Particulate filter for removing particulates, carbon monoxide, hydrocarbons and nitrogen oxides from the exhaust gas of internal combustion engines operated with a stoichiometric air/fuel mixture, comprising a wall-flow filter of length L and a coating Z, wherein the wall-flow filter comprises channels E and A which extend in parallel between a first and a second end of the wall-flow filter and which are separated by porous walls forming surfaces OE and OA, and wherein the channels E are closed at the second end and the channels A are closed at the first end, wherein coating Z is located within the porous walls and extends over the length L from the first end of the wall-flow filter and comprises active aluminium oxide, at least two different cerium/zirconium/rare-earth metal mixed oxides and at least one platinum group metal, characterised in that the second cerium/zirconium/rare-earth metal mixed oxide comprises two rare-earth metals and the content of the second rare-earth metal is 2% to 15% by weight of the second cerium/zirconium/rare-earth metal mixed oxide, and both cerium/zirconium/rare-earth metal mixed oxides are activated with palladium and rhodium, platinum and rhodium or platinum, palladium and rhodium.
  2. Particulate filter according to claim 1, characterised in that the weight ratio of aluminium oxide to the sum of the two cerium/zirconium/rare earth metal mixed oxides lies in the range from 10:90 to 60:40.
  3. Particulate filter according to claim 1 and/or 2, characterised in that the weight ratio of the first cerium/zirconium/rare earth metal mixed oxide to the second cerium/zirconium/rare earth metal mixed oxide lies in the range from 4:1 to 1:4.
  4. A particulate filter according to one of the preceding claims, characterised in that the first cerium/zirconium/rare earth metal mixed oxide has a higher zirconium oxide content than the second cerium/zirconium/rare earth metal mixed oxide.
  5. A particulate filter according to one of the preceding claims, characterised in that the first cerium/zirconium/rare-earth metal mixed oxide has a weight ratio of cerium oxide to zirconium oxide of 0.7 to 0.1, which is lower than in the second cerium/zirconium/rare-earth metal mixed oxide, which has a weight ratio of cerium oxide to zirconium oxide of 0.5 to 1.5.
  6. A particulate filter according to any one of the preceding claims, characterised in that the first cerium/zirconium/rare earth metal mixed oxide has a cerium oxide content of 10% to 40% by weight of the first cerium/zirconium/rare earth metal mixed oxide.
  7. A particulate filter according to one of the preceding claims, characterised in that the first cerium/zirconium/rare earth metal mixed oxide has a zirconium oxide content of 40% to 90% by weight of the first cerium/zirconium/rare earth metal mixed oxide.
  8. A particulate filter according to one of the preceding claims, characterised in that the second cerium/zirconium/rare earth metal mixed oxide has a cerium oxide content of 25% to 60% by weight of the second cerium/zirconium/rare earth metal mixed oxide.
  9. A particulate filter according to one of the preceding claims, characterised in that the second cerium/zirconium/rare earth metal mixed oxide has a zirconium oxide content of 20% to 70% by weight of the second cerium/zirconium/rare earth metal mixed oxide.
  10. A particulate filter according to one of the preceding claims, characterised in that both cerium/zirconium/rare earth metal mixed oxides are doped with lanthanum oxide.
  11. A particulate filter according to one of the preceding claims, characterised in that the content of lanthanum oxide is >0% to 10% by weight of the respective cerium/zirconium/rare earth metal mixed oxide.
  12. A particulate filter according to one of the preceding claims, characterised in that the first cerium/zirconium/rare earth metal mixed oxide is doped with yttrium oxide in addition to lanthanum oxide.
  13. A particulate filter according to one of the preceding claims, characterised in that the yttrium oxide content of the first cerium/zirconium/rare earth metal mixed oxide is 2% to 25% by weight of the first cerium/zirconium/rare earth metal mixed oxide.
  14. A particulate filter according to any one of the preceding claims, characterised in that the second cerium/zirconium/rare earth metal mixed oxide is doped with praseodymium in addition to lanthanum oxide.
  15. A method for removing particulates, carbon monoxide, hydrocarbons and nitrogen oxides from the exhaust gas of internal combustion engines operated with a stoichiometric air/fuel mixture, characterised in that the exhaust gas is passed through a particulate filter according to claims 1-14.

Description

The present invention relates to a catalytically active particulate filter, which is particularly suitable for the removal of particles, carbon monoxide, hydrocarbons and nitrogen oxides from the exhaust gas of internal combustion engines operated with stoichiometric air/fuel mixture. Exhaust gases from combustion engines running on a stoichiometric air/fuel mixture, such as gasoline or natural gas-powered spark-ignition engines, are cleaned using conventional methods with the aid of three-way catalytic converters. These are capable of simultaneously converting the three main gaseous pollutants of the engine—hydrocarbons, carbon monoxide, and nitrogen oxides—into harmless components. Stoichiometric means that, on average, exactly as much air is available for the combustion of the fuel present in the cylinder as is required for complete combustion. The air-fuel ratio λ (air/fuel ratio) relates the actual mass of air available for combustion, m<sub> L,tats </sub>, to the stoichiometric mass of air, m <sub>L,st</sub> . λ=mL,tatsmL,st If λ < 1 (e.g., 0.9), this means "lack of air," and the exhaust mixture is described as rich. If λ > 1 (e.g., 1.1), this means "excess air," and the exhaust mixture is described as lean. The statement λ = 1.1 means that there is 10% more air present than would be necessary for a stoichiometric reaction. In addition to gaseous pollutants, the exhaust gas from combustion engines also contains very fine particles (PM), which result from the incomplete combustion of the fuel and consist primarily of soot. Unlike the particulate emissions from diesel engines, the particles in the exhaust gas of stoichiometrically operated combustion engines, such as gasoline engines, are very small and exhibit a The average particle size is less than 1 µm. Typical particle sizes range from 10 nm to 200 nm. Furthermore, the amount of particles emitted is very low, ranging from 2 mg/km to 4 mg/km. The European emissions standard Euro 6c involves a change in the limit value for such particles from a particle mass limit to a more critical particle number limit of 6 x 10¹¹ /km (in the Worldwide Harmonised Light Vehicles Test Cycle - WLTP). This creates a need for exhaust aftertreatment concepts for stoichiometric combustion engines that include effective particle removal systems. In the field of exhaust gas cleaning from lean-burn engines, particularly diesel engines, wall-flow filters made of ceramic materials such as silicon carbide, aluminum titanate, and cordierite have proven effective. These filters consist of numerous parallel channels formed by porous walls. The channels are alternately closed at one end of the filter, creating channels A, which are open on one side and closed on the other, and channels B, which are closed on the first and open on the other. Exhaust gas flowing into channels A, for example, can only exit the filter via channels B and must therefore pass through the porous walls between channels A and B. As the exhaust gas passes through the wall, the particles are retained, and the exhaust gas is cleaned. The particles thus retained must subsequently be burned off or oxidized to prevent the filter from clogging or an unacceptable increase in the exhaust system's back pressure. For this purpose, the wall-mounted flow filter, for example, is coated with catalytically active coatings that lower the ignition temperature of soot. It is already known to apply such coatings to the porous walls between the channels (so-called on-wall coating) or to introduce them into the porous walls (so-called in-wall coating). EP 1657410 A2 This also describes a combination of both coating types, i.e., part of the catalytically active material is located in the porous walls and another part is located on the porous walls. The concept of removing particles from exhaust gas using wall flow filters has already been applied to the cleaning of exhaust gas from combustion engines operating with stoichiometric air/fuel mixtures; see, for example, the EP 2042226 A2 According to their theory, a wall flow filter has two layers arranged one above the other, one of which can be located in the porous wall and the other on the porous wall. A similar concept is pursued by the DE 102011050788 A1 . There, the porous filter walls contain a catalyst material of a three-way catalyst, while additionally a catalyst material of a three-way catalyst is applied to parts of the filter walls. FR 3020091 A1 The diagram reveals a particle filter that features a coating in its porous walls, as well as coatings on the surfaces of the inlet and outlet channels. The latter extend over a portion of the filter's length, specifically on both the inlet and outlet surfaces on the side of the filter where the exhaust gas enters. Other documents describing filter substrates with catalytically active coatings are: EP 3205388 A1 , EP 3207977 A1 , EP 3207978 A1 , EP 3207987 A1 , EP 3207989 A1 , EP 3207990 A1 , EP 3162428 A1 , EP 2650042 A1 , EP