Catalytically active particulate filter
The present invention relates to a particulate filter for removing particles, carbon monoxide, hydrocarbons and nitrogen oxides from the exhaust gas from internal combustion engines operated with a stoichiometric air-fuel mixture. Two coatings Y and Z are located in the porous walls and are present from the first end of the wall-flow filter over the entire length L of the particulate filter. Both contain active alumina, at least one cerium-zirconium-rare earth metal mixed oxide and at least one platinum group metal.
1. Particulate filter for removing particles, carbon monoxide, hydrocarbons, and nitrogen oxides out of the exhaust gas of combustion engines operated with a stoichiometric air/fuel mixture, comprising a wall-flow filter of length L and two different coatings Y and 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 are separated by porous walls which form surfaces OE or OA, and wherein the channels E are closed at the second end and the channels A are closed at the first end,
characterized in that
the two coatings Y and Z are located in the porous walls and extend from the first end of the wall-flow filter over the entire length L and both comprise active alumina, at least one oxygen storage material, and at least one platinum group metal, and wherein the at least one oxygen storage material in coating Z comprises two different cerium-zirconium-rare earth metal mixed oxides.
2. Particulate filter according to claim 1 ,
characterized in that
the weight ratio of active alumina to the sum of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z is in the range from 10:90 to 60:40.
3. Particulate filter according to claim 1 ,
wherein the weight ratio of a first cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z to a second cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z is in the range from 4:1 to 1:4.
4. Particulate filter according to claim 1 ,
wherein a first cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z has a higher zirconium oxide content than a second cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z.
5. Particulate filter according to claim 1 ,
wherein a first cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z has a lower cerium oxide content than a second cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z.
6. Particulate filter according to claim 1 , wherein the at least one oxygen storage material in coating Y comprises at least one cerium-zirconium-rare earth metal mixed oxide.
7. Particulate filter according to claim 1 ,
characterized in that
a first cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z has a cerium oxide to zirconium oxide weight ratio of 0.1 to 0.7, which is smaller than that in a second cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z, which has a cerium oxide to zirconium oxide weight ratio of 0.5 to 1.5.
8. Particulate filter according to claim 6 ,
characterized in that
the at least one cerium-zirconium-rare earth metal mixed oxide of coating Y has a cerium oxide to zirconium oxide weight ratio of 0.1 to 0.7.
9. Particulate filter according to claim 6 ,
characterized in that
all cerium-zirconium-rare earth metal mixed oxides in coatings Y and Z are doped with lanthanum oxide.
10. Particulate filter according to claim 1 ,
wherein a first cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z is doped with lanthanum oxide as well as 2% to 25% yttrium oxide based on the weight of the first cerium-zirconium-rare earth metal mixed oxide.
11. Particulate filter according to claim 10 ,
wherein a second cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z is doped with lanthanum oxide as well as 2% to 10% praseodymium oxide based on the weight of the second cerium-zirconium-rare earth metal mixed oxide.
12. Particulate filter according to claim 6 ,
wherein the at least one cerium-zirconium-rare earth metal mixed oxide of coating Y is doped with lanthanum oxide as well as 2% to 25% yttrium oxide based on the weight of the at least one first cerium-zirconium-rare earth metal mixed oxide yttrium oxide of coating Y.
13. Particulate filter according to claim 12 ,
wherein a first cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z comprises yttrium oxide, and
the mass fraction of yttrium oxide is greater in the coating Y than in the coating Z.
14. Particulate filter according to claim 1 ,
wherein each of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z are activated with palladium, platinum, or palladium and platinum.
15. Particulate filter according to claim 6 ,
characterized in that
each cerium-zirconium-rare earth metal mixed oxide of the coatings Y and Z is activated with palladium or rhodium, or palladium and rhodium.
16. Particulate filter according to claim 1 ,
characterized in that the ratio of the applied quantity of coating Z to the applied quantity of coating Y is in the range from 3:1 to 1:3.
17. Method for removing particles, carbon monoxide, hydrocarbons and nitrogen oxides out of the exhaust gas of combustion engines operated with a stoichiometric air/fuel mixture, characterized in that the exhaust gas is passed over a particulate filter according to claim 1 .
18. Particulate filter according to claim 6 ,
characterized in that
the weight ratio of active alumina to the at least one cerium-zirconium-rare earth metal mixed oxide in coating Y is in the range from 25:75 to 75:25.
19. Particulate filter for removing particles, carbon monoxide, hydrocarbons and nitrogen oxides out of the exhaust gas of combustion engines operated with a stoichiometric air-fuel mixture, comprising a wall-flow filter of length L and two different coatings Y and 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 are separated by porous walls which form 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, characterized in that the two coatings Y and Z are located in the porous walls and extend from the first end of the wall-flow filter over the entire length L and both comprise active alumina, at least one cerium-zirconium-rare earth metal mixed oxide and at least one platinum group metal, wherein layer Z is free of rhodium, and that the ratio of the applied quantity of coating Z to the applied quantity of coating Y is in the range from 3:1 to 1:3, and wherein the at least one cerium-zirconium-rare earth metal mixed oxide in coating Z comprises two different cerium-zirconium-rare earth metal mixed oxides.
20. Particulate filter according to claim 19 , wherein,
a first cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z is doped with lanthanum oxide as well as 2% to 25% yttrium oxide based on the weight of the first cerium-zirconium-rare earth metal mixed oxide; and
wherein a second cerium-zirconium-rare earth metal mixed oxide of the two different cerium-zirconium-rare earth metal mixed oxides of coating Z is doped with lanthanum oxide as well as 2% to 10% praseodymium oxide based on the weight of the second cerium-zirconium-rare earth metal mixed oxide.