Multi-component filters for emissions control
Catalytic articles, systems and methods for treating exhaust gas streams are described. A catalytic article comprising a wall flow filter having gas permeable walls, a hydrolysis catalyst, an optional soot oxidation catalyst, a selective catalytic reduction catalyst permeating the walls, an ammonia oxidation catalyst and an oxidation catalyst to oxidize CO and hydrocarbons is described. Methods of treating exhaust gas streams comprising soot, an ammonia precursor such as urea, ammonia, NO x , CO and hydrocarbons are also provided.
1. A catalytic article to remove emissions from a gas stream containing soot, ammonia, an ammonia precursor, NO x , CO and hydrocarbons, the article comprising:
a wall-flow filter for trapping soot in the gas stream, the filter having an inlet end and an outlet end defining an overall length, gas permeable walls having a thickness formed into a plurality of axially extending inlet channels and outlet channels, each inlet channel having inlet walls, an open inlet end and an outlet plug at the outlet end, each outlet channel having outlet walls, inlet plugs at the inlet end and an open outlet end, with each inlet channel having adjacent outlet channels;
a selective catalytic reduction catalyst permeating the gas permeable walls, the selective catalytic reduction catalyst promoting the conversion of NO x in the gas stream to N 2 in the presence of excess oxygen;
an ammonia oxidation catalyst coating a length of the outlet walls of the outlet channels that promotes the selective oxidation of ammonia to N 2 in the gas stream, wherein the ammonia oxidation catalyst extends up to about 50% of the overall length of the catalytic article; and
an oxidation catalyst coated on a portion of the outlet walls of the outlet channels extending from the outlet end toward the inlet end that promotes the oxidation of CO and hydrocarbons to CO 2 , wherein there is substantially no overlap of the oxidation catalyst on the ammonia catalyst.
2. The catalytic article of claim 1 , wherein the oxidation catalyst extends from the outlet end a length of about the same as a length of the outlet plugs.
3. The catalytic article of claim 1 , wherein the oxidation catalyst comprises a platinum group metal on a high surface area support.
4. The catalytic article of claim 1 , further comprising an hydrolysis catalyst that promotes the hydrolysis of the ammonia precursor, the hydrolysis catalyst coated on a portion of the inlet walls of the inlet channels extending from the inlet end.
5. The catalytic article of claim 1 , wherein the selective catalytic reduction catalyst extends along the entire length of the wall flow filter.
6. The catalytic article of claim 1 , wherein the selective catalytic reduction catalyst has a loading in the range of about 0.25 g/in 3 to about 2.5 g/in 3 .
7. The catalytic article of claim 1 , wherein the selective catalytic reduction catalyst comprises a metal promoted molecular sieve.
8. The catalytic article of claim 7 , wherein the molecular sieve comprises a zeolite having a framework selected from the group consisting of CHA, FAU, BEA, MFI, MOR and combinations thereof.
9. The catalytic article of claim 7 , wherein the molecular sieve comprises a zeolite with a CHA framework, an SAR greater than about 15.
10. The catalytic article of claim 9 , wherein the molecular sieve comprises copper in an amount greater than about 0.2 wt %.
11. A catalytic article to remove emissions from a gas stream containing soot, ammonia, an ammonia precursor, NO x , CO and hydrocarbons, the article comprising:
a wall-flow filter for trapping soot in the gas stream, the filter having an inlet end and an outlet end defining an overall length, gas permeable walls having a thickness formed into a plurality of axially extending inlet channels and outlet channels, each inlet channel having inlet walls, an open inlet end and an outlet plug at the outlet end, each outlet channel having outlet walls, inlet plugs at the inlet end and an open outlet end, with each inlet channel having adjacent outlet channels;
a selective catalytic reduction catalyst permeating the gas permeable walls, the selective catalytic reduction catalyst having a loading the range of about 0.25 g/in 3 to about 2.5 g/in 3 and promoting the conversion of NO x in the gas stream to N 2 in the presence of excess oxygen;
an ammonia oxidation catalyst coating a length of the outlet walls of the outlet channels that promotes the selective oxidation of ammonia to N 2 in the gas stream; and
an oxidation catalyst coated on a portion of the outlet walls of the outlet channels extending from the outlet end toward the inlet end that promotes the oxidation of CO and hydrocarbons to CO 2 .
12. The catalytic article of claim 11 , wherein the selective catalytic reduction catalyst comprises a metal promoted molecular sieve.
13. The catalytic article of claim 12 , wherein the molecular sieve comprises a zeolite having a framework selected from the group consisting of CHA, FAU, BEA, MFI, MOR and combinations thereof.
14. The catalytic article of claim 12 , wherein the molecular sieve comprises a zeolite with a CHA framework, an SAR greater than about 15.
15. The catalytic article of claim 11 , wherein the ammonia oxidation catalyst extends from the oxidation catalyst up to about 50% of the overall length of the catalytic article.
16. A catalytic article to remove emissions from a gas stream containing soot, ammonia, an ammonia precursor, NO x , CO and hydrocarbons, the article comprising:
a wall-flow filter for trapping soot in the gas stream, the filter having an inlet end and an outlet end defining an overall length, gas permeable walls having a thickness formed into a plurality of axially extending inlet channels and outlet channels, each inlet channel having inlet walls, an open inlet end and an outlet plug at the outlet end, each outlet channel having outlet walls, inlet plugs at the inlet end and an open outlet end, with each inlet channel having adjacent outlet channels;
a selective catalytic reduction catalyst permeating the gas permeable walls, the selective catalytic reduction catalyst promoting the conversion of NO x in the gas stream to N 2 in the presence of excess oxygen;
a soot oxidation catalyst upstream of the selective catalytic reduction catalyst;
an ammonia oxidation catalyst coating a length of the outlet walls of the outlet channels that promotes the selective oxidation of ammonia to N 2 in the gas stream; and
an oxidation catalyst coated on a portion of the outlet walls of the outlet channels extending from the outlet end toward the inlet end that promotes the oxidation of CO and hydrocarbons to CO 2 .
17. The catalytic article of claim 16 , wherein the soot oxidation catalyst permeates the gas permeable walls.
18. The catalytic article of claim 17 , wherein the soot oxidation catalyst comprises a layer permeating an inlet side of the gas permeable walls.
19. The catalytic article of claim 18 , wherein the layer permeates the gas permeable walls to a depth up to about 50% of the wall thickness.
20. The catalytic article of claim 16 , wherein the soot oxidation catalyst comprises a layer on the inlet walls.
21. The catalytic article of claim 16 , wherein the soot oxidation catalyst comprises zirconia stabilized cerium oxide.
22. A catalytic article to remove emissions from a gas stream containing soot, ammonia, an ammonia precursor, NO x , CO and hydrocarbons, the article comprising:
a wall-flow filter for trapping soot in the gas stream, the filter having an inlet end and an outlet end defining an overall length, gas permeable walls having a thickness formed into a plurality of axially extending inlet channels and outlet channels, each inlet channel having inlet walls, an open inlet end and an outlet plug at the outlet end, each outlet channel having outlet walls, inlet plugs at the inlet end and an open outlet end, with each inlet channel having adjacent outlet channels;
a selective catalytic reduction catalyst permeating the gas permeable walls, the selective catalytic reduction catalyst promoting the conversion of NO in the gas stream to N 2 in the presence of excess oxygen;
an ammonia oxidation catalyst coating a length of the outlet walls of the outlet channels that promotes the selective oxidation of ammonia to N 2 in the gas stream; and
an oxidation catalyst coated on a portion of the outlet walls of the outlet channels extending from the outlet end up to about 2 inches toward the inlet end, the oxidation catalyst promoting the oxidation of CO and hydrocarbons to CO 2 .
23. A catalytic article to remove emissions from a gas stream containing soot, ammonia, an ammonia precursor, NO x , CO and hydrocarbons, the article comprising:
a wall-flow filter for trapping soot in the gas stream, the filter having an inlet end and an outlet end defining an overall length, gas permeable walls having a thickness formed into a plurality of axially extending inlet channels and outlet channels, each inlet channel having inlet walls, an open inlet end and an outlet plug at the outlet end, each outlet channel having outlet walls, inlet plugs at the inlet end and an open outlet end, with each inlet channel having adjacent outlet channels;
a selective catalytic reduction catalyst permeating the gas permeable walls, the selective catalytic reduction catalyst promoting the conversion of NO x in the gas stream to N 2 in the presence of excess oxygen;
an ammonia oxidation catalyst coating a length of the outlet walls of the outlet channels that promotes the selective oxidation of ammonia to N 2 in the gas stream; and
an oxidation catalyst coated on a portion of the outlet walls of the outlet channels extending from the outlet end toward the inlet end that promotes the oxidation of CO and hydrocarbons to CO 2 , wherein there is substantially no overlap of the oxidation catalyst on the ammonia catalyst, and wherein the ammonia oxidation catalyst extends from the oxidation catalyst up to about 50% of the overall length of the catalytic article.
24. The catalytic article of claim 23 , further comprising a hydrolysis catalyst that promotes the hydrolysis of the ammonia precursor, the hydrolysis catalyst coated on a portion of the inlet walls of the inlet channels extending from the inlet end.
25. The catalytic article of claim 24 , wherein the selective catalytic reduction catalyst has a loading in the range of about 0.25 g/in 3 to about 2.5 g/in 3 .