Low temperature NOx reduction using H

1. An emission treatment system for selectively reducing NOx compounds, the system comprising:

a hydrogen generator; and

an H 2 -SCR catalytic article comprising a substrate and an H 2 -SCR catalyst composition, the hydrogen generator being in fluid communication with, and upstream of, the H 2 -SCR catalytic article;

wherein the H 2 -SCR catalyst composition comprises a platinum group metal component with a metal loading ranging from 0.1% to 1% by weight of the H 2 -SCR catalyst composition supported on a support consisting of (i) a hydrogen form of zeolite, (ii) a metal oxide selected from the group consisting of zirconia, titania, magnesia, and combinations thereof, or (iii) combinations of (i) and (ii); and

at least one of (a) a diesel oxidation catalyst (DOC) catalyst composition; and (b) a lean NOx trap (LNT) composition,

wherein when the LNT composition is present, the system comprises a lean NOx trap (LNT) catalytic article comprising a substrate and the LNT catalyst composition, the LNT catalytic article in fluid communication with, and downstream of, the H 2 -SCR catalytic article, and

wherein when the DOC catalyst composition is present, the DOC catalyst composition is

present in a zoned catalyst coating on the H 2 -SCR catalytic article with an upstream zone comprising the H 2 -SCR catalyst composition and a downstream zone comprising the DOC catalyst composition.

2. The emission treatment system according to claim 1 , further comprising a low temperature NOx adsorbent (LTNA) catalyst composition present in the zoned catalyst coating.

3. The emission treatment system according to claim 2 , wherein, in the zoned catalyst coating, the LTNA catalyst composition is incorporated into the upstream zone comprising the H 2 -SCR catalyst composition, incorporated into the downstream zone comprising the DOC composition, or positioned in a middle zone between the upstream zone comprising the H 2 -SCR catalyst composition and the downstream zone comprising the DOC composition.

4. The emission treatment system according to claim 1 , further comprising a low temperature NOx adsorbent (LTNA) catalytic article comprising a substrate and a LTNA catalyst composition, the LTNA catalytic article in fluid communication with the H 2 -SCR catalytic article and the hydrogen generator.

5. The emission treatment system according to claim 4 , wherein the LTNA catalytic article is positioned downstream from the H 2 -SCR catalytic article or positioned upstream from the H 2 SCR catalytic article and the hydrogen generator.

6. The emission treatment system according to claim 1 , wherein the LNT catalyst composition comprises a NOx sorbent and a platinum group metal component dispersed on a refractory metal oxide support.

7. The emission treatment system according to claim 1 , wherein the H 2 -SCR catalytic article is close coupled.

8. The emission treatment system according to claim 1 , wherein the platinum group metal component is platinum, palladium, or a combination thereof.

9. A method for treating an exhaust stream containing NOx, comprising passing the exhaust stream through the emission treatment system of claim 1 .

10. The method according to claim 9 , wherein the exhaust stream has a temperature that is about 200° C. or lower, about 175° C. or lower, about 150° C. or lower, about 125° C. or lower, or about 100° C. or lower.

11. The emission treatment system according to claim 1 , further comprising a catalytic soot filter (CSF), a selective catalytic reduction (SCR) catalyst, an ammonia oxidation catalyst (AMOX), or combinations thereof.

12. The emission treatment system according to claim 11 , wherein the SCR catalyst comprises a base metal-containing 8-ring small pore molecular sieve.

13. The emission treatment system according to claim 12 , wherein the SCR catalyst comprises an iron and/or copper-containing 8-ring small pore molecular sieve.

14. The emission treatment system according to claim 13 , wherein the molecular sieve is a zeolite having a structure selected from the group consisting of AEI, AFT, AFX, CHA, EAB, EM, KFI, LEV, SAS, SAT, and SAV.

15. The emission treatment system according to claim 14 , wherein the molecular sieve has a CHA crystal structure.

16. A method for treating an exhaust stream containing NOx, comprising:

introducing hydrogen gas into the exhaust stream to form a hydrogen-treated exhaust stream;

passing the hydrogen-treated exhaust stream through an emission treatment system comprising

an H 2 SCR catalytic article comprising a substrate and an H 2 SCR catalyst composition,

wherein the H 2 SCR catalyst composition comprises a platinum group metal component with a metal loading ranging from 0.1% to 1% by weight of the H 2 -SCR catalyst composition supported on a support consisting of (i) a hydrogen form of zeolite, (ii) a metal oxide selected from the group consisting of zirconia, titania, magnesia, and combinations thereof, or (iii) combinations of (i) and (ii); and

at least one of (a) a diesel oxidation catalyst (DOC) catalyst composition; and (b) a lean NOx trap (LNT) composition,

wherein when the LNT composition is present, the system comprises a lean NOx trap (LNT) catalytic article comprising a substrate and the LNT catalyst composition, the LNT catalytic article in fluid communication with, and downstream of, the H 2 -SCR catalytic article, and

wherein when the DOC catalyst composition is present, the DOC catalyst composition is

present in a zoned catalyst coating on the H 2 -SCR catalytic article with an upstream zone comprising the H 2 -SCR catalyst composition and a downstream zone comprising the DOC catalyst composition.

17. The method according to claim 16 , wherein the platinum group metal component is platinum, palladium, or a combination thereof.

18. The emission treatment system according to claim 1 , wherein the hydrogen generator is selected from the group consisting of on board hydrogen, hydrogen produced from alcohol reforming, hydrogen produced from ammonia decomposition, and combinations thereof.