PASSIVE NOx ADSORBER

Abstract

A NO x absorber catalyst for treating an exhaust gas from a diesel engine. The NO x absorber catalyst comprises a first NO x absorber material comprising a molecular sieve catalyst, wherein the molecular sieve catalyst comprises a noble metal and a molecular sieve, and wherein the molecular sieve contains the noble metal; a second NO x absorber material comprising palladium (Pd) supported on an oxide of cerium; and a substrate having an inlet end and an outlet end.

1 . A NO x  absorber catalyst for treating an exhaust gas from a diesel engine comprising:
 a first NO x  absorber material comprising a molecular sieve catalyst, wherein the molecular sieve catalyst comprises a noble metal and a molecular sieve, and wherein the molecular sieve contains the noble metal;   a second NO x  absorber material comprising palladium (Pd) supported on an oxide of cerium; and   a substrate having an inlet end and an outlet end.   
     
     
         2 . A NO x  absorber catalyst according to  claim 1 , wherein the noble metal comprises palladium. 
     
     
         3 . A NO x  absorber catalyst according to  claim 1 , wherein the molecular sieve has an aluminosilicate framework, an aluminophosphate framework or a silico-aluminophosphate framework. 
     
     
         3 . A NO x  absorber catalyst according to  claim 1 , wherein the molecular sieve is selected from a small pore molecular sieve, a medium pore molecular sieve and a large pore molecular sieve. 
     
     
         4 . A NO x  absorber catalyst according to  claim 1 , wherein the molecular sieve is a small pore molecular sieve having a Framework Type selected from the group consisting of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON and a mixture or intergrowth of any two or more thereof. 
     
     
         5 . A NO x  absorber catalyst according to  claim 4 , wherein the small pore molecular sieve has a Framework Type that is AEI or CHA. 
     
     
         6 . A NO x  absorber catalyst according to  claim 1 , wherein the molecular sieve has an aluminosilicate framework and a silica to alumina molar ratio of 10 to 200. 
     
     
         7 . A NO x  absorber catalyst according to  claim 1 , wherein the oxide of cerium is ceria (CeO 2 ) or a mixed or composite oxide of ceria and a second oxide selected from alumina and zirconia. 
     
     
         8 . A NO x  absorber catalyst according to  claim 1 , wherein the oxide of cerium is doped with a dopant, wherein the dopant is an element selected from the group consisting of tungsten (W), silicon (Si), titanium (Ti), lanthanum (La), praseodymium (Pr), hafnium (Hf), yttrium (Y), ytterbium (Yb), samarium (Sm), neodymium (Nd) and a combination of two or more thereof, or an oxide thereof. 
     
     
         9 . A NO x  absorber catalyst according to  claim 1 , wherein the concentration of palladium (Pd) is ≦2% by weight of the concentration of the oxide of cerium. 
     
     
         10 . A NO x  absorber catalyst according to  claim 1 , which comprises a mixture of the first NO x  absorber material and the second NO x  absorber material. 
     
     
         11 . A NO x  absorber catalyst according to  claim 1 , wherein the NO x  absorber catalyst comprises a first zone and a second zone, wherein the first zone comprises the first NO x  absorber material, and the second zone comprises the second NO x  absorber material. 
     
     
         12 . A NO x  absorber catalyst according to  claim 11 , wherein the first zone is disposed upstream of the second zone or the first zone is disposed downstream of the second zone. 
     
     
         13 . A NO x  absorber catalyst according to  claim 1 , which comprises a first region and a second region, wherein the first region comprises the first NO x  absorber material, and the second region comprises the second NO x  absorber material, and wherein either the first region overlaps the second region or the second region overlaps the first region. 
     
     
         14 . A NO x  absorber catalyst according to  claim 1 , which comprises a first layer and a second layer, wherein the first layer comprises the first NO x  absorber material, and the second layer comprises the second NO x  absorber material, and wherein either the first layer is disposed on the second layer or the second layer is disposed on the first layer. 
     
     
         15 . A NO x  absorber catalyst according to any  claim 1  further comprising a diesel oxidation catalyst (DOC) region. 
     
     
         16 . A NO x  absorber catalyst according to  claim 1 , wherein the substrate is a flow-through monolith or a filtering monolith. 
     
     
         17 . An exhaust system comprising a NO x  absorber catalyst as defined in any one of  claim 1  and an emissions control device. 
     
     
         18 . An exhaust system according to  claim 17 , wherein the emissions control device is selected from the group consisting of emissions control device selected from the group consisting of a diesel particulate filter (DPF), a lean NO x  trap (LNT), a lean NO x  catalyst (LNC), a selective catalytic reduction (SCR) catalyst, a diesel oxidation catalyst (DOC), a catalysed soot filter (CSF), a selective catalytic reduction filter (SCRF™) catalyst, an ammonia slip catalyst (ASC) and combinations of two or more thereof. 
     
     
         19 . A vehicle comprising a lean burn engine and an exhaust system as defined in  claim 17 . 
     
     
         20 . A vehicle according to  claim 19 , wherein the lean burn engine is configured to run on diesel fuel comprising ≦50 ppm of sulfur.