Catalyst materials for ammonia oxidation in lean-burn engine exhaust

Abstract

An exhaust aftertreatment system and a method for treating exhaust produced by a lean-burn engine are provided. The exhaust aftertreatment system may include an exhaust gas treatment subsystem and a clean-up oxidation catalyst located downstream of the exhaust gas treatment subsystem. The clean-up oxidation catalyst can selectively oxidize NH 3 to N 2 in the hot, oxygen-abundant exhaust flow emanated from the lean-burn engine and passed through the exhaust gas treatment subsystem to help prevent ammonia slip to the atmosphere. The clean-up oxidation catalyst comprises perovskite oxide particles and/or manganese-containing mixed metal oxide particles dispersed on a selective catalytic reduction (SCR) catalyst.

What is claimed is: 
     
         1 . An exhaust aftertreatment system for removing gaseous emissions and suspended particulate matter, if present, contained in exhaust produced by a lean-burn engine that is combusting a lean mixture of air and fuel, the exhaust aftertreatment system comprising:
 an exhaust gas treatment subsystem that receives an exhaust flow from the lean-burn engine and communicates an intermediate exhaust flow, the exhaust gas treatment subsystem comprising a NO X  abatement component and operating to oxidize carbon monoxide and unburned and/or partially burned hydrocarbons, remove suspended particulate matter if present, and reduce NO X  so that the intermediate exhaust flow comprises a lesser amount of carbon monoxide, unburned and/or partially burned hydrocarbons, suspended particulate matter if present, and NO X  than the exhaust flow; and   a clean-up oxidation catalyst that receives the intermediate exhaust flow from the exhaust gas treatment subsystem and communicates a treated exhaust flow, the treated exhaust flow being communicated to the atmosphere without being exposed to another catalyst material after the clean-up oxidation catalyst, the clean-up oxidation catalyst comprising (1) a selective catalytic reduction catalyst and (2) metal oxide particles dispersed on the selective catalytic reduction catalyst, wherein the metal oxide particles are selected from the group consisting of perovskite oxide particles, manganese-containing mixed metal oxide particles, and mixtures thereof, and wherein the metal oxide particles are present in an amount that ranges from about 0.1 wt. % to about 20 wt. % based on the weight of the clean-up oxidation catalyst.   
     
     
         2 . The exhaust aftertreatment system set forth in  claim 1 , wherein the perovskite oxide particles comprise at least one of LaCoO 3 , La 0.9 Sr 0.1 CoO 3 , LaMnO 3 , La 0.9 Sr 0.1 MnO 3 , LaFeO 3 , or LaSr 0.1 Fe 0.9 O 3 , and wherein the manganese-containing mixed metal oxide particles comprise at least one of Mn X Ce Y O Z , Mn X Zr W O Z , or Mn X Ce Y Zr W O Z  in which X ranges from 0.02 to 0.98, Y ranges from 0.02 to 0.98, W ranges from 0.02 to 0.98, and Z ranges from 1.0 to 3.0. 
     
     
         3 . The exhaust aftertreatment system set forth in  claim 1 , wherein the selective catalytic reduction catalyst comprises silver-supported alumina, an ion-exchanged base-metal zeolite, or a base metal oxide selected from the group consisting of V 2 O 5 -WO 3 /TiO 2 , V 2 O 5 /TiO 2 , and mixtures thereof. 
     
     
         4 . The exhaust aftertreatment system set forth in  claim 3 , wherein the ion-exchanged base-metal zeolite comprises at least one of a β-zeolite that is ion-exchanged with at least one of a Cu or Fe, a MFI-type zeolite that is ion-exchanged with at least one of a Cu or Fe, or a Y-type zeolite that is ion-exchanged with at least one of a Na, Ba, Cu, Co, or CuCo. 
     
     
         5 . The exhaust aftertreatment system set forth in  claim 1 , wherein the amount of metal oxide particles dispersed on the selective catalytic reduction catalyst ranges from about 0.5 wt. % to about 15 wt. % based on the weight of the clean-up oxidation catalyst. 
     
     
         6 . The exhaust aftertreatment system set forth in  claim 1 , wherein the amount of metal oxide particles dispersed on the selective catalytic reduction catalyst ranges from about 1.0 wt. % to about 12 wt. % based on the weight of the clean-up oxidation catalyst. 
     
     
         7 . The exhaust aftertreatment system set forth in  claim 1 , wherein the NO X  abatement component is a lean NO X  trap that comprises a LNT catalyst. 
     
     
         8 . The exhaust aftertreatment system set forth in  claim 7 , wherein the exhaust gas treatment subsystem further comprises at least one of a diesel oxidation converter or a catalytic converter located upstream of the lean-NO X  trap, wherein the diesel oxidation converter comprises a diesel oxidation catalyst and the catalytic converter comprises a three-way-catalyst. 
     
     
         9 . The exhaust aftertreatment system set forth in  claim 1 , wherein the NO X  abatement component is an ammonia-SCR catalytic converter that comprises an ammonia-SCR catalyst. 
     
     
         10 . The exhaust aftertreatment system set forth in  claim 9 , wherein the exhaust gas treatment subsystem further comprises at least one of a diesel oxidation converter or a catalytic converter located upstream of the ammonia-SCR catalytic converter, wherein the diesel oxidation converter comprises a diesel oxidation catalyst and the catalytic converter comprises a three-way-catalyst. 
     
     
         11 . The exhaust aftertreatment system set forth in  claim 9 , wherein the exhaust gas treatment subsystem further comprises a urea-metering device that introduces urea into the exhaust flow to form an exhaust mixture that comprises ammonia and the exhaust flow, and wherein the ammonia-SCR catalytic converter receives the exhaust mixture. 
     
     
         12 . The exhaust aftertreatment system set forth in  claim 1 , wherein the clean-up oxidation catalyst is carried on a support body and housed in a canister that is fluidly connected to the exhaust gas treatment subsystem. 
     
     
         13 . A method for removing gaseous emissions and suspended particulate matter, if present, contained in exhaust produced by a lean-burn engine that is combusting a lean mixture of air and fuel, the method comprising:
 supplying a lean-burn engine with a lean mixture of air and fuel;   combusting the lean mixture of air and fuel in the lean-burn engine to produce an exhaust flow;   delivering the exhaust flow to an exhaust gas treatment subsystem that comprises a NO X  abatement component that can catalytically reduce NO X  to N 2 ;   operating the exhaust gas treatment subsystem to produce an intermediate exhaust flow that comprises a lesser amount of carbon monoxide, unburned and/or partially burned hydrocarbons, suspended particulate matter if present, and NO X  than the exhaust flow; and   delivering the intermediate exhaust flow to a clean-up oxidation catalyst to oxidize ammonia, if present, and produce a treated exhaust flow, the clean-up oxidation catalyst comprising (1) a selective catalytic reduction catalyst and (2) metal oxide particles dispersed on the selective catalystic reduction catalyst, wherein the metal oxide particles are selected from the group consisting of perovskite oxide particles, manganese-containing mixed metal oxide particles, and mixtures thereof.   
     
     
         14 . The method set forth in  claim 13 , further comprising communicating the treated exhaust flow to the atmosphere without exposing the treated exhaust flow to another catalyst material after the clean-up oxidation catalyst. 
     
     
         15 . The method set forth in  claim 13 , wherein operating the exhaust gas treatment subsystem comprises:
 delivering the exhaust flow to a diesel oxidation converter or a catalytic converter, the diesel oxidation converter comprising a diesel oxidation catalyst and the catalytic converter comprising a three-way-catalyst; and   delivering the exhaust flow to a lean-NO X  trap that includes a LNT catalyst that includes an oxidation catalyst, a NO X  storage catalyst, and a NO X  reduction catalyst.   
     
     
         16 . The method set forth in  claim 13 , wherein operating the exhaust gas treatment subsystem comprises:
 delivering the exhaust flow to a diesel oxidation converter or a catalytic converter, the diesel oxidation converter comprising a diesel oxidation catalyst and the catalytic converter comprising a three-way-catalyst;   introducing ammonia into the exhaust flow to form an exhaust mixture; and   delivering the exhaust mixture to an ammonia-SCR catalytic converter that comprises an ammonia-SCR catalyst.   
     
     
         17 . The method set forth in  claim 13 , wherein the metal oxide particles comprise at least one of LaCoO 3 , La 0.9 Sr 0.1 CoO 3 , LaMnO 3 , La 0.9 Sr 0.1 MnO 3 , LaFeO 3 , LaSr 0.1 Fe 0.9 O 3 , Mn X Ce Y O Z , Mn X Zr W O Z , or Mn X Ce Y Zr W O Z  in which X ranges from 0.02 to 0.98 Y ranges from 0.02 to 0.98, W ranges from 0.02 to 0.98, and Z ranges from 1.0 to 3.0. 
     
     
         18 . The method set forth in  claim 13 , wherein the selective catalytic reduction catalyst comprises at least one of silver-supported alumina, an ion-exchanged base-metal zeolite, or a base metal oxide selected from the group consisting of V 2 O 5 -WO 3 /TiO 2 , V 2 O 5 /TiO 2 , and mixtures thereof. 
     
     
         19 . The method set forth in  claim 18 , wherein the ion-exchanged base-metal zeolite comprises at least one of a β-zeolite that is ion-exchanged with at least one of a Cu or Fe, a MFI-type zeolite that is ion-exchanged with at least one of a Cu or Fe, or a Y-type zeolite that is ion-exchanged with at least one of a Na, Ba, Cu, Co, or CuCo. 
     
     
         20 . The method set forth in  claim 13 , wherein the metal oxide particles are dispersed on the selective catalytic reduction catalyst in an amount that ranges from about 0.1 wt. % to about 20 wt. % based on the weight of the clean-up oxidation catalyst.