Exhaust system for a lean-burn internal combustion engine including scr catalyst

Abstract

An exhaust system 20 for an internal combustion engine comprises a) a first catalysed substrate monolith 12 comprising a first washcoat coating disposed in a first washcoat zone 16 of the substrate monolith and a second washcoat coating disposed in a second washcoat zone 18 of the substrate monolith, wherein the first washcoat coating comprises a catalyst composition comprising at least one platinum group metal (PGM) and at least one support material, wherein at least one PGM in the first washcoat coating is liable to volatilise when the first washcoat coating is exposed to relatively extreme conditions including relatively high temperatures, wherein the second washcoat coating comprises at least one material supporting copper for trapping volatilised PGM and wherein the second washcoat coating is oriented to contact exhaust gas that has contacted the first washcoat; and b) a second catalysed substrate monolith 14 comprising a catalyst for selectively catalysing the reduction of oxides of nitrogen to dinitrogen with a nitrogenous reductant disposed downstream from the first catalysed substrate monolith.

1 .- 18 . (canceled) 
     
     
         19 . A method of reducing or preventing a selective catalytic reduction (SCR) catalyst in an exhaust system of a lean-burn internal combustion engine from becoming poisoned with platinum group metal (PGM) which may volatilise from a catalyst composition of a first catalysed substrate monolith comprising at least one platinum group metal (PGM) supported on at least one support material and disposed on a substrate monolith upstream of the selective catalytic reduction (SCR) catalyst of a second catalysed substrate monolith when the catalyst composition comprising platinum group metal (PGM) is exposed to relatively extreme conditions including relatively high temperatures, which method comprising trapping volatilised platinum group metal (PGM) in a washcoat coating comprising at least one material supporting copper, which is disposed on the same substrate monolith as the catalyst composition comprising platinum group metal (PGM). 
     
     
         20 . The method according to  claim 19 , wherein the exhaust system comprises an injector for injecting a nitrogenous reductant into exhaust gas between the first catalysed substrate monolith and the second catalysed substrate monolith. 
     
     
         21 . The method according to  claim 19 , wherein the first catalysed substrate monolith comprises a first washcoat coating comprising the at least one platinum group metal (PGM), wherein the at least one platinum group metal (PGM) comprises platinum. 
     
     
         22 . The method according to  claim 19 , wherein the first catalysed substrate monolith comprises a first washcoat coating comprising the at least one platinum group metal (PGM), wherein the at least one platinum group metal (PGM) comprises both platinum and palladium. 
     
     
         23 . The method according to  claim 22 , wherein a weight ratio of Pt: Pd is ≦2. 
     
     
         24 . The method according to  claim 19 , wherein the at least one support material is at least one metal oxide, a molecular sieve or a mixture of any two or more thereof. 
     
     
         25 . The method according to  claim 24 , wherein the or each metal oxide support is selected from the group consisting of optionally stabilised alumina, amorphous silica-alumina, optionally stabilised zirconia, ceria, titania, an optionally stabilised ceria-zirconia mixed oxide and a mixture of any two or more thereof. 
     
     
         26 . The method according to  claim 24 , wherein the molecular sieve is an aluminosilicate zeolite. 
     
     
         27 . The method according to  claim 19 , wherein the first substrate monolith is a flow-through substrate monolith. 
     
     
         28 . The method according to  claim 19 , wherein the first substrate monolith is a filtering substrate monolith having inlet surfaces and outlet surfaces, wherein the inlet surfaces are separated from the outlet surfaces by a porous structure and wherein the first washcoat coating of the first zone is applied to the inlet surfaces and the second washcoat coating of the second zone is applied to the outlet surfaces. 
     
     
         29 . The method according to  claim 28 , wherein the filtering substrate monolith is a wall-flow filter, wherein inlet channels of the wall-flow filter comprise the first zone and wherein outlet channels of the wall-flow filter comprise the second zone. 
     
     
         30 . The method according to  claim 19 , wherein the second substrate monolith is a flow-through substrate monolith. 
     
     
         31 . The method according to  claim 19 , wherein the second substrate monolith is a filtering substrate monolith having inlet surfaces and outlet surfaces, wherein the inlet surfaces are separated from the outlet surfaces by a porous structure. 
     
     
         32 . The method according to  claim 32 , wherein the filtering substrate monolith is a wall-flow filter. 
     
     
         33 . The method according to  claim 19 , wherein the first washcoat comprises an oxidation catalyst or a NO x  adsorber catalyst. 
     
     
         34 . The method according to  claim 19 , comprising a third substrate monolith, wherein the third substrate monolith is a filtering substrate monolith, which third substrate monolith is disposed downstream of the second catalysed substrate monolith. 
     
     
         35 . The method according to  claim 34 , wherein the third substrate monolith comprises an oxidation catalyst.