Treatment Systems and Methods for Internal Combustion Engine Exhaust Streams

Abstract

Emissions treatment systems and methods are disclosed, which reduce the carbon monoxide, unburned hydrocarbons, and nitrogen oxides content in the exhaust stream of an internal combustion engine adjusted to a rich combustion ratio. One embodiment of a system comprises an ammonia oxidation catalyst, a supplemental air supply for providing a lean combustion ratio, and at least one three-way catalyst. Another embodiment further comprises a second three-way catalyst located in the exhaust stream.

1 . An emissions treatment system for reducing carbon monoxide, unburned hydrocarbons, and nitrogen oxides content in an exhaust gas stream of an internal combustion engine adjusted to a rich combustion ratio comprising:
 an ammonia oxidation catalyst;   a supplemental air source for supplying supplemental air upstream of the ammonia oxidation catalyst; and   a first three-way catalyst located to receive and pass the exhaust gas from the engine through the first three-way catalyst, wherein the internal combustion engine is adjusted to the rich combustion ratio.   
   
   
       2 . The emissions treatment system of  claim 1 , wherein the first three-way catalyst is located upstream of the supplemental air source. 
   
   
       3 . The emissions treatment system of  claim 1 , wherein the first three-way catalyst is located downstream from the ammonia oxidation catalyst, and the supplemental air source is upstream of the ammonia oxidation catalyst. 
   
   
       4 . The emissions treatment system of  claim 2  further comprising a second three-way catalyst located downstream from the ammonia oxidation catalyst. 
   
   
       5 . The emissions treatment system of  claim 4  wherein:
 the first three-way catalyst comprises a precious metal component and a rare earth oxide deposited on a substrate;   the ammonia oxide catalyst comprises a precious metal component; a zeolite component containing a base metal oxide selected from the group consisting of oxides of chromium, manganese, iron, cobalt, nickel, copper, vanadium, titanium, zinc, and combinations thereof and a silica component; deposited on a substrate; and   the second three-way catalyst comprises a precious metal component and a rare earth oxide deposited on a substrate.   
   
   
       6 . The emissions treatment system of  claim 1  wherein the first three-way catalyst comprises a precious metal component selected from the group consisting of platinum, palladium, rhodium, and combinations thereof; and a rare earth oxide selected from the group consisting of ceria, lanthana, praseodymia, neodymia, and combinations thereof. 
   
   
       7 . The emissions treatment system of  claim 1  wherein the first three-way catalyst comprises:
 a first catalytic layer deposited on a substrate comprising a platinum component in an amount in the range of about 12.5 to about 100 g/ft 3 , an alumina support in an amount in the range of about 0.2 to about 2.0 g/in 3 , a ceria-zirconia composite in an amount in the range of about 0.2 to about 1.0 g/in 3 , a zirconium component in an amount in the range of about 0.03 to about 0.15 g/in 3 , and a barium component in an amount in the range of about 0.03 to about 0.15 g/in 3 ; and   a second catalytic layer deposited on the first catalytic layer comprising a rhodium component in an amount of about 12.5 to about 100 g/ft 3 , an alumina support in an amount in the range of about 0.2 to about 2.0 g/in 3 , a ceria-zirconia composite in an amount in the range of about 0.2 to about 1.0 g/in 3 , and a zirconium component in an amount in the range of about 0.03 to about 0.15 g/in 3 .   
   
   
       8 . The emissions treatment system of  claim 1  wherein the ammonia oxidation catalyst comprises a layer deposited on a substrate comprising a platinum component in an amount in the range of about 1 to about 25 g/ft 3 , a zeolite component in an amount in the range of about 0.5 to about 2.5 g/in 3 , wherein the zeolite component contains iron, and a silica component in an amount in the range of about 0.1 to about 1.5 g/in 3 . 
   
   
       9 . The emissions treatment system of  claim 4  wherein the second three-way catalyst comprises a precious metal component selected from the group consisting of platinum, palladium, rhodium, and combinations thereof; and a rare earth oxide selected from the group consisting of ceria, lanthana, praseodymia, neodymia, and combinations thereof. 
   
   
       10 . The emissions treatment system of  claim 4  wherein a monolithic substrate comprises a first discrete portion including a coating of the ammonia oxidation catalyst, and a second discrete portion including a coating of the second three-way catalyst. 
   
   
       11 . The emissions treatment system of  claim 10  wherein the monolithic substrate selected from the group consisting of a ceramic material with a multiplicity of passageways therethrough, a metallic material being in the form of an expanded matrix, and a metallic material being in the form of a flat or corrugated metal foil configured in a multiplicity of layers. 
   
   
       12 . The emissions treatment system of  claim 3  wherein:
 the ammonia oxidation catalyst comprises a platinum component in an amount in the range of about 1 to about 25 g/ft 3 , and is effective to selectively oxidize at least about 99% of ammonia formed in the first three-way catalyst to nitrogen and water, and to selectively reduce the nitrogen oxides to nitrogen; and   the first three-way catalyst comprises a precious metal component, a base metal oxide selected from the group consisting of oxides of chromium, manganese, iron, cobalt, nickel, copper, vanadium, titanium, zinc, and combinations thereof, and a rare earth oxide deposited on a substrate, and is effective to oxidize at least about 99% of the unburned hydrocarbon to carbon dioxide and water, oxidize at least about 99% of the carbon monoxide to carbon dioxide.   
   
   
       13 . The emissions treatment system of  claim 12  wherein the ammonia oxidation catalyst comprises a zeolite component in an amount in the range of about 0.5 to about 2.5 g/in 3 , wherein the zeolite of contains iron or a copper-oxide copper-nitrate composite in an amount in the range of about 0.1 to about 0.5 g/in 3  and a silica component in an amount in the range of about 0.1 to about 1.5 g/in 3 . 
   
   
       14 . The emissions treatment system of  claim 12  wherein the first three-way catalyst comprises a first catalytic layer deposited on the substrate comprising a platinum component in an amount in the range of about 12.5 to about 100 g/ft 3 , an alumina support in an amount in the range of about 0.2 to about 2.0 g/in 3 , a ceria-zirconia composite in an amount in the range of about 0.2 to about 1.0 g/in 3 , a zirconium component in the range of about 0.03 to about 0.15 g/in 3 , and a barium component in an amount in the range of about 0.03 to about 0.15 g/in 3 ; and
 a second catalytic layer deposited on the first catalytic layer, the second catalytic layer comprising a rhodium component in the range of about 12.5 to about 100 g/ft 3 , an alumina support in an amount in the range of about 0.2 to about 2.0 g/in 3 , a ceria-zirconia composite in the range of about 0.2 to about 1.0 g/in 3 , and a zirconium component in the range of about 0.03 to about 0.15 g/in 3 .   
   
   
       15 . A method for reducing carbon monoxide, unburned hydrocarbons, and nitrogen oxides in an exhaust stream of an internal combustion engine comprising:
 providing the internal combustion engine adjusted to a rich combustion ratio;   passing the exhaust stream through a first three-way catalyst;   adding sufficient air to the exhaust stream, upstream of an ammonia oxidation catalyst, to provide a lean combustion ratio; and   passing the exhaust stream through the ammonia oxidation catalyst.   
   
   
       16 . The method of  claim 15 , wherein passing the exhaust stream through the ammonia oxidation catalyst occurs after passing the exhaust stream through the first three-way catalyst. 
   
   
       17 . The method of  claim 16 , further comprising passing the exhaust stream exiting the ammonia oxidation catalyst through a second three-way catalyst. 
   
   
       18 . The method of  claim 15  further comprising providing a sufficient amount of the first three-way catalyst to oxidize at least about 50% of the carbon monoxide to carbon dioxide, and to oxidize at least about 50% of the unburned hydrocarbons to carbon dioxide and water, and providing a sufficient amount of the ammonia oxidation catalyst to selectively oxidize at least about 99% of ammonia formed in the first three-way catalyst to nitrogen and water. 
   
   
       19 . The method of  claim 17  further comprising providing a sufficient amount of the second three-way catalyst to oxidize at least about 99% of the unburned hydrocarbons entering the second three-way catalyst to carbon dioxide and water, and about 99% of the carbon monoxide entering the second three-way catalyst to carbon dioxide. 
   
   
       20 . An exhaust system for reducing the carbon monoxide, unburned hydrocarbons, and nitrogen oxides content in an exhaust stream of an internal combustion engine adjusted to a rich stoichiometric ratio comprising:
 an exhaust conduit located to receive exhaust from the engine;   a first three-way catalyst located to receive and pass the exhaust gas through the first three-way catalyst, the first three-way catalyst comprising a first catalytic layer deposited on a first substrate comprising a platinum component in an amount in the range of about 12.5 to about 100 g/ft 3 , an alumina support in an amount in the range of about 0.2 to about 2.0 g/in 3 , a ceria-zirconia composite in an amount in the range of about 0.2 to about 1.0 g/in 3 , a zirconium component in the range of about 0.03 to about 0.15 g/in 3 , and a barium component in an amount in the range of about 0.03 to about 0.15 g/in 3 ; and   a second catalytic layer deposited on the first catalytic layer, the second catalytic layer comprising a rhodium component in the range of about 12.5 to about 100 g/ft 3 , an alumina support in an amount in the range of about 0.2 to about 2.0 g/in 3 , a ceria-zirconia composite in the range of about 0.2 to about 1.0 g/in 3 , and a zirconium component in the range of about 0.03 to about 0.15 g/in 3 , wherein the first substrate comprises a metallic foil substrate comprising a multiplicity of layers, each having the first three-way catalyst deposited thereon;   an air source having an inlet to the exhaust downstream from the first three-way catalyst for introducing sufficient air into the exhaust stream to provide a lean combustion ratio;   an ammonia oxidation catalyst downstream from the air source comprising a layer deposited on a second substrate comprising a platinum component in an amount in the range of about 1 to about 25 g/ft 3 , a zeolite component in an amount in the range of about 0.5 to about 2.5 g/in 3 , wherein the zeolite of contains iron or a copper-oxide copper-nitrate composite in an amount in the range of about 0.1 to about 0.5 g/in 3  and a silica component in an amount in the range of about 0.1 to about 1.5 g/in 3 , wherein the second substrate comprises a metallic foil substrate comprising a multiplicity of layers, each having the ammonia oxidation catalyst deposited thereon; and   a second three-way catalyst downstream from the ammonia oxidation catalyst comprising a comprising a first catalytic layer deposited on a third substrate comprising a platinum component in an amount in the range of about 12.5 to about 100 g/ft 3 , an alumina support in an amount in the range of about 0.2 to about 2.0 g/in 3 , a ceria-zirconia composite in an amount in the range of about 0.2 to about 1.0 g/in 3 , a zirconium component in an amount in the range of about 0.03 to about 0.15 g/in 3 , and a barium component in an amount in the range of about 0.03 to about 0.15 g/in 3 ; and a second catalytic layer deposited on the first catalytic layer comprising a rhodium component in an amount of about 12.5 to about 100 g/ft 3 , an alumina support in an amount in the range of about 0.2 to about 2.0 g/in 3 , a ceria-zirconia composite in an amount in the range of about 0.2 to about 1.0 g/in 3 , and a zirconium component in an amount in the range of about 0.03 to about 0.15 g/in 3 , wherein the third substrate comprises a metallic foil substrate comprising a multiplicity of layers, each having the second three-way catalyst deposited thereon.