Lean NO

1. An emission treatment system for NO x abatement in an exhaust stream of a lean burn engine, the emission treatment system comprising:

a lean NO x trap (LNT) comprising an oxygen storage component (OSC) and a first platinum group metal (PGM) component, wherein the LNT is in fluid communication with and downstream from the lean burn engine; and

a low-temperature NO x adsorber (LT-NA) comprising a molecular sieve comprising a second PGM component, wherein the LT-NA is in fluid communication with and downstream of the LNT,

wherein the LNT and LT-NA are disposed on a substrate in a zoned configuration, the substrate having an inlet end and an outlet end defining an overall length;

wherein the LNT is disposed on the substrate extending from the inlet end to a length of from about 20% to about 100% of the overall length; and

wherein the LT-NA is disposed on the substrate extending from the outlet end to a length of from about 20% to about 100% of the overall length.

2. The emission treatment system of claim 1 , wherein the LNT is disposed on a first substrate, and the LT-NA is disposed on a second substrate.

3. The emission treatment system of claim 2 , wherein the first substrate is a honeycomb substrate in the form of a flow-through filter, and the second substrate is a honeycomb substrate in the form of a flow-through filter or a wall-flow filter.

4. The emission treatment system of claim 1 , wherein the LNT is disposed directly on the substrate covering 100% of the overall length; and the LT-NA is disposed on the LNT, covering from about 20% to about 80% of the overall length.

5. The emission treatment system of claim 1 , wherein the LT-NA is disposed directly on the substrate covering 100% of the overall length; and the LNT is disposed on the LT-NA, covering from about 20% to about 80% of the overall length.

6. The emission treatment system of claim 1 , wherein the LNT is disposed directly on the substrate, and the LT-NA is disposed directly on the substrate.

7. The emission treatment system of claim 1 , wherein the substrate is a honeycomb substrate in the form of a flow-through filter.

8. The emission treatment system f claim 1 , wherein the OSC comprises ceria.

9. The emission treatment system of claim 8 , wherein the OSC further comprises one or more chosen from zirconia, alumina, silica, titanic, lanthana, baric, praseodymia, yttria, samaria, gadolinia, and combinations thereof.

10. The emission treatment system of claim 1 , wherein the first PGM component is chosen from platinum, palladium, rhodium, and combinations thereof, and second PGM component is chosen from platinum, palladium, rhodium, and combinations thereof.

11. The emission treatment system of claim 1 , wherein the second PGM component resides in ion-exchanged sites in the molecular sieve.

12. The emission treatment system of claim 1 , wherein the molecular sieve has a framework type chosen from ABW, ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFG, AFR, AFS, AFT, AFX, AFY, AHT, ANA, APC, APD, AST, ASV, ATN, ATO, ATS, ATT, ATV, AVL, AWO, AWW, BCT, BEA, BEC, BIK, BOF, BOG, BOZ, BPH, BRE, BSV, CAN, CAS, CDO, CR, CGF, CGS, CHA, CHI, CLO, CON, CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EEI, EMT, EON, EPI, ERI, ESV, ETR, EUO, EZT, FAU, FER, FRA, GIS, GiU, GME, CON, GOO, HEU, IFR, IFY, IHW, IMF, IRN, ISV, ITE, ITG, ITH, ITW, IWR, IWS, IWV, IWW, JBW, JRY, JSR, JST, KR, LAU, LEV, LIO, LIT, LOS, LOV, LTA, LTF, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS, MON, MOR, MOZ, MRE, MSE, MSO, MTF, MTN, MIT, MVY, MTW, MWF, MWW, NAB, NAT, NES, NON, NPO, NPT, NSI, OBW, OFF, OKO, OSI, OSO, OWE, PAR, PAU, PCR, PHI, PON, PUN, RHO, RON, RRO, RSN, RTE, RTH, RUT, RWR, RWY, SAF, SAO, SAS, SAT, SAV, SBE, SBS, SBT, SCO, SEW, SFE, SFF, SFO, SFH, SFN, SFO, SFS, SFW, SGF, SGT, SIV, SOD, SOF, SOS, SSF, SSY, STF, STI, STO, SIT, STW, SVR, SZR, TER, THO, TON, TSC, TUN, UEI, UR, UOS, UOZ, USI, UTL, UWY, VET, VFI, VNI, VSV, WIE, WEN, YUG, ZON, and mixtures or intergrowths thereof.

13. The emission treatment system of claim 1 , wherein the molecular sieve is an aluminosilicate zeolite.

14. The emission treatment system of claim 1 , wherein the molecular sieve is chosen from Type A, beta zeolite, chabazite, erionite, faujasite, ferrierite, mordenite, silicalite, SSZ-13, stilbite, ZSM-5, ZSM-11, ZSM-23, ZSM-48, zeolite X, and zeolite Y.

15. The emission treatment system of claim 1 , wherein the LNT is configured to remove reducing gases present during a rich condition; and wherein the LNT is configured to prevent the reducing gases from entering the downstream LT-NA.

16. The emission treatment system of claim 1 , further comprising a lambda sensor disposed downstream of the LNT.

17. The emission treatment system of claim 1 , further comprising one or more chosen from a selective catalytic reduction (SCR) catalyst, an ammonia or ammonia precursor injection component, a diesel oxidation catalyst (DOC), a catalyzed soot filter (CSF), an ammonia oxidation (AMOX) catalyst, and combinations thereof.

18. The emission treatment system of claim 17 , wherein the SCR catalyst is downstream of and in fluid communication with the LT-NA.

19. A method for abating NO x in an exhaust stream from a lean burn engine, the method comprising contacting the exhaust gas stream with the emission treatment system of claim 1 .

20. The method of claim 19 , further comprising:

operating the lean burn engine in a rich mode that produces a rich exhaust stream containing reducing gases comprising hydrocarbons (HC) and carbon monoxide (CO);

passing the rich exhaust gas stream through the LNT, thereby creating a reducing atmosphere therein; and

regenerating the LNT in the reducing atmosphere,

wherein the lean burn engine is operated in the rich mode to sufficiently regenerate the LNT without exceeding the adsorption capacity of the LNT for the reducing gases.

21. The method of claim 20 , further comprising:

monitoring the exhaust stream exiting the LNT with a lambda sensor; and

returning the lean burn engine to a lean mode to end operating the lean burn engine in the rich mode according to a monitoring result, thereby preventing exposure of the LT-NA to the reducing atmosphere.