Exhaust line for an internal combustion engine

Abstract

An exhaust system for an internal combustion engine comprises a catalysed particulate filter comprising a NOx absorbent capable of absorbing NOx contained in an exhaust gas when the composition of the exhaust gas is lambda >1, and capable of releasing the NOx absorbed in the NOx component when the exhaust gas composition is 1≧lambda, characterised in that the exhaust system further comprises a catalyst capable of oxidising NO to NO 2 at least when the air-fuel ration of the exhaust gas is lean.

1 . An exhaust system for an internal combustion engine, which system comprising a catalysed particulate filter comprising an oxidation catalyst comprising at least one platinum group metal selected from the group consisting of platinum and palladium and a NO x  absorbent comprising at least one metal selected from the group consisting of alkali metals, alkaline earth metals and a rare earth metals for absorbing NO x  contained in an exhaust gas when the composition of the exhaust gas is lambda >1, and for releasing the NO x  absorbed in the NO x  absorbent when the exhaust gas composition is 1≧lambda, and a platinum group metal catalyst upstream of the filter for oxidising NO to NO 2  at least when the composition of the exhaust gas is lambda >1.  
     
     
         2 . An exhaust system according to  claim 1 , wherein the particulate filter is a ceramic wall flow filter.  
     
     
         3 . An exhaust system according to  claim 1 , wherein the filter comprises rhodium.  
     
     
         4 . An exhaust system according to  claim 1 , wherein the platinum group metal in the platinum group metal catalyst comprises platinum and palladium.  
     
     
         5 . An internal combustion engine including an exhaust system according to  claim 1 .  
     
     
         6 . An engine according to  claim 5 , wherein it is a diesel engine.  
     
     
         7 . An engine according to  claim 6 , wherein the diesel engine is a heavy duty diesel engine.  
     
     
         8 . A method of treating an exhaust gas of an internal combustion engine, which method comprising oxidising NO in the exhaust gas to NO 2  at least when the composition of the exhaust gas is lambda >1, trapping particulate on a catalysed filter also including a NOx absorbent, oxidising NO to NO 2  on the filter when the composition of the exhaust gas is lambda >1, absorbing the NO 2  in the NO x  absorbent when the composition of the exhaust gas is lambda >1, releasing the absorbed NO x  as NO 2  when the exhaust gas composition is 1≧lambda and combusting particulate trapped on the filter in NO 27 , wherein the step of oxidising NO to NO 2  is performed upstream of the filter.  
     
     
         9 . A vehicle including an internal combustion engine according to  claim 5 .  
     
     
         10 . A method according to  claim 8 , wherein the step of combusting particulate is done at exhaust gas temperatures of up to 400° C.  
     
     
         11 . A method according to  claim 8 , wherein the particulate filter is a ceramic wall flow filter.  
     
     
         12 . A method according to  claim 8 , wherein the filter comprises rhodium.  
     
     
         13 . A method according to  claim 8 , wherein the filter comprises an oxidation catalyst comprising at least one platinum group metal selected from the group consisting of platinum and palladium and the NO x  absorbent  
     
     
         14 . A method according to  claim 13 , wherein the platinum group metal in the platinum group metal catalyst comprises platinum and palladium.