Exhaust System

Abstract

An exhaust system for an internal combustion engine, the exhaust system comprising, a lean NO x trap, and a wall flow monolithic substrate having a pre-coated porosity of 40% or greater, and comprising an oxidation catalytic zone, the oxidation catalytic zone comprising a platinum group metal loaded on a first support, the first support comprising at least one inorganic oxide and a zinc compound.

1 . An exhaust system for an internal combustion engine, the exhaust system comprising,
 a. a lean NO x  trap, and   b. a wall flow monolithic substrate having a pre-coated porosity of 40% or greater, and comprising an oxidation catalytic zone, the oxidation catalytic zone comprising a platinum group metal loaded on a first support, the first support comprising at least one inorganic oxide and a zinc compound.   
     
     
         2 . The exhaust system according to  claim 1 , wherein the zinc compound is selected from zinc oxide, zinc nitrate, zinc carbonate, zinc hydroxide or a mixture of two or more thereof. 
     
     
         3 . The exhaust system according to  claim 1 , wherein the inorganic oxide comprises cerium oxide. 
     
     
         4 . The exhaust system according to  claim 1 , wherein the first support further comprises alumina and/or an aluminate. 
     
     
         5 . The exhaust system as claimed in  claim 1 , wherein the first support comprises alumina and ceria-zirconia mixed oxide. 
     
     
         6 . The exhaust system according to  claim 1 , wherein the zinc compound has a particle size according to d 90  in the range 1 to 25 μm. 
     
     
         7 . (canceled) 
     
     
         8 . The exhaust system according to  claim 1 , wherein the platinum group metal is selected from the group consisting of platinum, palladium, rhodium, and a mixtures of any two or more thereof. 
     
     
         9 . The exhaust system according to  claim 8 , wherein the platinum group metal comprises a mixture of platinum and palladium in a Pt:Pd weight ratio in the range 0.5:1 to 7:1. 
     
     
         10 . (canceled) 
     
     
         11 . The exhaust system according to  claim 1 , wherein the pre-coated porosity of the wall flow monolithic substrate is 41% or greater. 
     
     
         12 . (canceled) 
     
     
         13 . (canceled) 
     
     
         14 . (canceled) 
     
     
         15 . The exhaust system according to  claim 1 , wherein the oxidation catalyst zone is applied to be in a single layer. 
     
     
         16 . (canceled) 
     
     
         17 . The exhaust system according to  claim 1 , further comprising a selective catalytic reduction zone on a monolithic substrate, the selective catalytic reduction zone comprising copper or iron loaded on a second support, the second support comprising a molecular sieve. 
     
     
         18 . The exhaust system according to  claim 17 , wherein the molecular sieve is selected from the group consisting of a beta zeolite (BEA), a faujasite (FAU), an L-zeolite, a chabazite, a ZSM zeolite, a small pore molecular sieve having a maximum pore opening of eight tetrahedral atoms, an SSZ-zeolite, a ferrierite (FER), a mordenite (MOR), an offretite (OFF), a clinoptilolite (HEU), a silicalite, an aluminophosphate molecular sieve, a mesoporous zeolite, and/or mixtures of any two or more thereof. 
     
     
         19 . (canceled) 
     
     
         20 . The exhaust system according to  claim 17 , wherein the oxidation catalyst zone is on a first wall flow monolithic substrate and the selective catalytic reduction zone is on a second monolithic substrate. 
     
     
         21 . The exhaust system according to  claim 17 , wherein the oxidation catalyst zone and the selective catalytic reduction zone are each on portions of the same wall flow monolithic substrate. 
     
     
         22 . The exhaust system according to  claim 21 , wherein the oxidation catalyst zone is disposed in channels of the wall flow monolithic substrate from one end thereof and the selective catalytic reduction zone is disposed in channels of the wall flow monolithic substrate from the other end thereof. 
     
     
         23 . The exhaust system according to  claim 22 , wherein the oxidation catalyst zone extends over between 10% and 90% of the axial length of the monolithic substrate and the selective catalytic reduction zone extends over between 90% and 10% of the axial length of the monolithic substrate. 
     
     
         24 . (canceled) 
     
     
         25 . The exhaust system according to  claim 1 , wherein the wall flow monolithic substrate comprises pores having a diameter, the pores of the wall flow monolithic substrate have a diameter in the range 9 μm to 25 μm. 
     
     
         26 . The exhaust system according to  claim 1 , wherein the wall flow monolithic substrate comprises an inlet end having inlet channels and an outlet end having outlet channels and the oxidation catalyst zone is on and/or within the walls of the inlet channels of the inlet end of the monolithic substrate and/or within the walls of the outlet channels of the outlet end of the monolithic substrate. 
     
     
         27 . A catalytic wall flow monolithic substrate, the wall flow monolithic substrate having a oxidation catalyst zone thereon, the wall flow monolithic substrate having a pre-coated porosity of 40% or greater, the oxidation catalyst zone comprising a platinum group metal loaded on a first support, the first support comprising at least one inorganic oxide, and a zinc compound. 
     
     
         28 . (canceled) 
     
     
         29 . A method of making a catalysed monolithic substrate, the method comprising:
 a. providing a wall flow monolithic substrate, the wall flow monolithic substrate having a pre-coated porosity of 40% or greater,   b. preparing a oxidation catalyst zone washcoat comprising a source of a platinum group metal, a first support comprising at least one inorganic oxide and a source of a zinc compound, and   c. applying the oxidation catalyst zone washcoat to a first portion of the monolithic substrate.   
     
     
         30 . (canceled) 
     
     
         31 . A method of treating exhaust gases from an internal combustion engine, the method comprising flowing the exhaust gas through an exhaust system according to  claim 1 , wherein the exhaust gas comprises a lean exhaust gas intermittently becoming rich. 
     
     
         32 . A compression ignition engine fitted with an exhaust system according to  claim 1 . 
     
     
         33 . A vehicle comprising a compression ignition engine fitted with an exhaust system according to  claim 32 .