Partial filter substrates containing SCR catalysts and methods and emissions treatment systems
Catalytic articles, methods and emissions treatment systems for treating an engine exhaust gas stream containing NO x and particulate matter are disclosed and include a particulate filter comprising a first SCR catalyst for NO x conversion disposed downstream of the injector. The particulate filter is a partial filter with a particle filtration efficiency between about 30% and 60% and an SCR catalyst loading in the range of 0.1 g/in 3 -3.5 g/in 3 .
1. A catalytic article for use in a system for treating an engine exhaust gas stream containing an initial NO x concentration and particulate matter, the gas stream producing a system back pressure and a system NO x conversion, the catalytic article comprising:
a particulate filter comprising a first SCR catalyst effective for NO x conversion, the particulate filter having a particle filtration efficiency in the range of about 30% to 60% by mass and having a catalyst loading in the range of about 0.5 g/in 3 and 3.5 g/in 3 , wherein the particulate filter comprises a foam having an open or reticulated structure comprising cells and struts forming cellular walls, the foam defining a tortuous flow path for the engine exhaust gas stream and having a porosity between 50% and 95%.
2. The catalytic article of claim 1 , wherein the particulate filter has an axial length and the SCR catalyst is disposed on a zone extending less than the full axial length of the filter.
3. The catalytic article of claim 1 , wherein the SCR catalyst comprises a zeolite having a CHA structure.
4. The catalytic article of claim 1 , wherein the SCR catalyst comprises a molecular sieve containing at least one of Cu, Fe, Mn, Co, Ag and combinations thereof.
5. The catalytic article of claim 1 , wherein the particulate filter comprises a metal foam.
6. The catalytic article of claim 1 , wherein the SCR catalyst loading is in the range of about 0.5 g/in 3 to 2.0 g/in 3 .
7. A diesel engine emissions treatment system comprising the catalytic article of claim 1 downstream from an engine, and further comprising an oxidation catalyst disposed upstream of the particulate filter.
8. The emissions treatment system of claim 7 , wherein there is no intervening SCR catalyst disposed between the engine and the particulate filter.
9. The emissions treatment system of claim 7 , wherein the first SCR catalyst provides a NO x conversion of at least about 10% at 250° C. and a space velocity of about 40,000 h −1 when tested in a gas stream that comprises about 500 ppm NO, about 500 ppm NH 3 and about 5% water in air.
10. An emissions treatment system comprising the catalytic article of claim 1 , and a flow through substrate loaded with a second SCR catalyst effective for NO x conversion disposed downstream of the particulate filter, wherein conversion of NO x by the particulate filter is in the range of about 10% to 100% of the system total NO x conversion.
11. The emissions treatment system of claim 10 , further comprising an oxidation catalyst disposed upstream of the particulate filter.
12. The emissions treatment system of claim 10 , wherein the first SCR catalyst provides a NO conversion of at least about 10% at 250° C. and a space velocity of about 40,000 h −1 when tested in a gas stream that comprises about 500 ppm NO, about 500 ppm NH 3 and about 5% water in air.
13. The catalytic article of claim 1 , wherein the foam has a porosity between 60% and 95%.
14. The catalytic article of claim 1 , wherein the cells have a mean cell diameter in the range of 0.5 to 5 mm.
15. The catalytic article of claim 1 , wherein the foam has a pores per inch ranging from 3 to 100.
16. The catalytic article of claim 1 , wherein the foam has a pores per inch ranging from 30 to 90.
17. The catalytic article of claim 1 , wherein the foam has a pores per inch ranging from 40 to 70.
18. The catalytic article of claim 5 , wherein the metal foam comprises a metal selected from the group consisting of iron, titanium, tantalum, tungsten, noble metals, copper, nickel, bronze, aluminum, zirconium, and combinations and alloys thereof.
19. A method of treating an engine exhaust gas stream containing an initial NO x concentration and effective for conversion of NO x , the gas stream having a system back pressure and a system NO x conversion, the method comprising:
passing the engine exhaust gas stream produced by an engine through the catalytic article of claim 1 .
20. The method of treating an engine exhaust gas stream of claim 19 , wherein there is no intervening SCR catalyst disposed between the engine and the catalytic article.
21. The method of treating an engine exhaust gas stream of claim 19 , wherein a gas stream having an intermediate NO x concentration is produced by the catalyst article, the method further comprising:
injecting ammonia or an ammonia precursor into the exhaust gas system upstream of the catalyst article; and
passing the gas stream having the intermediate NO x concentration through a second substrate loaded with a second SCR catalyst disposed downstream of the catalyst article.
22. The method of treating an engine exhaust gas stream of claim 21 , wherein there is no intervening SCR catalyst disposed between the engine and the particulate filter.