# US 8,539,760 B2 · Catalyst materials for NOx oxidation in an exhaust aftertreatment system that uses passive ammonia SCR > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,539,760 B2 - Document ID: US8539760B2 - Status: Granted - Kind: B2 - Application number: 12/881,233 - Filed: 2010-09-14 - Published: 2012-03-15 - Granted: 2013-09-24 - Earliest claimed: 2010-09-14 - Assignees: GM Global Technology Operations LLC - Applicants: Wei Li; Chang H Kim; Kevin L. Perry; Paul M. Najt; Kushal Narayanaswamy - Inventors: Wei Li; Chang H Kim; Kevin L. Perry; Paul M. Najt; Kushal Narayanaswamy - Web page: https://patentgrep.com/patent/US8539760B2 ## CPC - B01D 53/9445: {Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]} - B01D 53/9422: {for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)} - B01D 53/944: {Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation catalysts (three-way-catalysts [TWC] B01D53/9445)} - B01D 53/9477: {with catalysts positioned on separate bricks, e.g. exhaust systems} - F01N 3/101: {Three-way catalysts} - F01N 3/103: {Oxidation catalysts for HC and CO only} - F01N 3/2066: {Selective catalytic reduction [SCR]} - F01N 3/2073: {Means for generating a reducing substance from the exhaust gases} - F01N 13/009: {having two or more separate purifying devices arranged in series} - B01D 2255/204: Alkaline earth metals - B01D 2255/2063: Lanthanum - B01D 2255/20746: Cobalt - B01D 2255/402: Perovskites - B01D 2255/911: NH3-storage component incorporated in the catalyst - B01D 2258/012: Diesel engines and lean burn gasoline engines - F01N 2370/02: used in catalytic reactors - Y02T 10/12: Improving ICE efficiencies - B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28) - F01N: GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES (arrangements in connection with gas exhaust of propulsion units in vehicles B60K13/00; combustion-air intake silencers specially adapted for, or arranged on, internal-combustion engines F02M35/00; protecting against, or damping, noise in general G10K11/16) - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract An exhaust aftertreatment system that receives an exhaust flow from a lean-burn engine and a method for treating the exhaust flow are described. The exhaust aftertreatment system may include a three-way-catalyst, an oxidation catalyst, and a NH3—SCR catalyst. The three-way-catalyst passively generates NH3 from native NOX contained in the exhaust flow when an A/F mixture supplied to the engine is cycled from lean to rich. The generated NH3 is then stored in the NH3—SCR catalyst to facilitate NOX reduction when the A/F mixture supplied to the engine is cycled back to lean. The oxidation catalyst is located upstream of the NH3—SCR catalyst and operates to lower the NO to NO2 molar ratio of the NOX fed to the NH3—SCR catalyst. The oxidation catalyst comprises perovskite oxide particles. ## Claims ### Claim 1 An exhaust aftertreatment system for removing gaseous emissions contained in an exhaust flow produced by a lean-burn that is supplied with and combusts an A/F mixture, the exhaust aftertreatment system comprising: a three-way-catalyst; an oxidation catalyst positioned downstream of the three-way-catalyst, the oxidation catalyst comprising perovskite oxide particles in an amount that ranges from about 50 g/L to about 200 g/L; and an ammonia-selective catalytic reduction (NH3—SCR) catalyst positioned downstream of the oxidation catalyst, the NH3—SCR catalyst being able to absorb NH3 when the A/F mixture is rich of stoichiometry and reduce NOX to N2 when the A/F mixture is lean of stoichiometry. ### Claim 2 (depends on 1) The exhaust aftertreatment system set forth in claim 1, wherein the oxidation catalyst comprises perovskite oxide particles that comprise at least one of LaCoO3, La0.9Sr0.1CoO3, LaMnO3, La0.9Sr0.1MnO3, LaFeO3, or La0.9Sr0.1FeO3. ### Claim 3 (depends on 1) The exhaust aftertreatment system set forth in claim 1, wherein the amount of perovskite oxide particles ranges from about 100 g/L to about 150 g/L. ### Claim 4 (depends on 1) The exhaust aftertreatment system set forth in claim 1, wherein the oxidation catalyst does not include any platinum group metals. ### Claim 5 (depends on 1) The exhaust aftertreatment system set forth in claim 1, wherein the three-way-catalyst comprises a combination of platinum, palladium, and rhodium. ### Claim 6 (depends on 1) The exhaust aftertreatment system set forth in claim 1, wherein the NH3—SCR catalyst comprises an ion-exchanged base-metal zeolite that is ion-exchanged with at least one of Na, Ba, V, Ti, W, Cu, Fe, or combinations thereof. ### Claim 7 (depends on 1) The exhaust aftertreatment system set forth in claim 1, wherein the oxidation catalyst further comprises a base material on which the perovskite oxide particles are washcoated. ### Claim 8 (depends on 7) The exhaust aftertreatment system set forth in claim 7, wherein the base material comprises at least one of a zeolite, a mixture of cerium oxide and zirconium oxide, or alumina. ### Claim 9 A method comprising: providing a lean-burn spark-ignition engine that is supplied with and combusts a mixture of air and fuel (A/F mixture) to produce an exhaust flow that comprises carbon monoxide (CO), unburned and/or partially burned hydrocarbons (HC's), and nitrogen oxides (NOX), the NOX comprising NO and NO2 in a molar ratio; delivering the exhaust flow to an exhaust aftertreatment system that comprises a three-way-catalyst, an oxidation catalyst positioned downstream of the three-way-catalyst, and a ammonia-selective catalytic reduction (NH3—SCR) catalyst positioned downstream of the oxidation catalyst, the oxidation catalyst comprising perovskite oxide particles in an amount that ranges from about 50 g/L to about 200 g/L, and the NH3—SCR catalyst being able to absorb NH3 when the exhaust flow promotes a reducing environment and reduce NOX to N2 in the presence of NH3 absorbed by the NH3—SCR catalyst when the exhaust flow promotes an oxidizing environment; supplying the A/F mixture to the lean-burn spark-ignition engine lean of stoichiometry to promote the oxidizing environment in the exhaust flow and to oxidize CO and HC's over the three-way-catalyst, oxidize NO to NO2 over the oxidation catalyst, and reduce NOX to N2 over the NH3—SCR catalyst when the NH3—SCR catalyst comprises absorbed NH3; and cycling the A/F mixture from lean to rich to promote the reducing environment in the exhaust flow and to passively generate NH3 over the three-way-catalyst and communicate the NH3 across the oxidation catalyst and to the NH3—SCR catalyst for absorption by the NH3—SCR catalyst. ### Claim 10 (depends on 9) The method set forth in claim 9, wherein the oxidation catalyst comprises perovskite oxides particles that comprise at least one of LaCoO3, La0.9Sr0.1CoO3, LaMnO3, La0.9Sr0.1MnO3, LaFeO3, or La0.9Sr0.1FeO3. ### Claim 11 (depends on 9) The method set forth in claim 9, wherein the amount of perovskite oxide particles ranges from about 100 g/L to about 150 g/L. ### Claim 12 (depends on 9) The method set forth in claim 9, wherein the three-way-catalyst comprises a combination of platinum, palladium, and rhodium, and wherein the NH3—SCR catalyst comprises an ion-exchanged base-metal zeolite that is ion-exchanged with at least one of Na, Ba, V, Ti, W, Cu, Fe, or combinations thereof. ### Claim 13 (depends on 9) The method set forth in claim 9, wherein the oxidation catalyst oxidizes NO to NO2 so that the molar ratio of NO to NO2 in the exhaust flow delivered to the NH3—SCR catalyst is between about 0.33 and 1 when the A/F mixture supplied to the lean-burn spark-ignition engine is lean of stoichiometry. ### Claim 14 (depends on 9) The method set forth in claim 9, wherein the oxidation catalyst further comprises a base material on which the perovskite oxide particles are washcoated, the base material comprising at least one of a zeolite, a mixture of cerium oxide and zirconium oxide, or alumina. ### Claim 15 A method comprising: supplying a mixture of air and fuel (A/F mixture) that is lean of stoichiometry to a lean-burn spark-ignition engine; combusting the A/F mixture that is lean of stoichiometry in the lean-burn spark-ignition engine to produce a first exhaust flow that promotes an oxidizing environment, the first exhaust flow comprising carbon monoxide (CO), unburned and/or partially burned hydrocarbons (HC's), and nitrogen oxides (NOX), the NOX comprising NO and NO2 in a molar ratio greater than about 4; delivering the first exhaust flow to a three-way-catalyst to oxidize CO and HC's; delivering the first exhaust flow to an oxidation catalyst that comprises perovskite oxide particles to oxidize NO to NO2 and decrease the molar ratio of NO to NO2 to a range of about 0.33 to about 1, the oxidation catalyst being positioned downstream of the three-way-catalyst; delivering the first exhaust flow to an ammonia-selective catalytic reduction (NH3—SCR) catalyst to reduce NOX to N2, the NH3—SCR catalyst comprising an amount of absorbed NH3 that reduces NOX to N2 in the oxidizing environment of the first exhaust flow, the NH3—SCR catalyst being positioned downstream of the oxidation catalyst; and replenishing the amount of absorbed NH3 in the NH3—SCR catalyst by cycling the A/F mixture from lean of stoichiometry to rich of stoichiometry to produce a second exhaust flow that promotes a reducing environment and delivering the second exhaust flow to the three-way-catalyst to passively generate NH3 for absorption by the NH3—SCR catalyst. ### Claim 16 (depends on 15) The method set forth in claim 15, wherein the oxidation catalyst comprises perovskites oxides particles that comprise at least one of LaCoO3, La0.9Sr0.1CoO3, LaMnO3, La0.9Sr0.1MnO3, LaFeO3, or La0.9Sr0.1FeO3. ### Claim 17 (depends on 15) The method set forth in claim 15, wherein the amount of perovskite oxide particles in the oxidation catalyst ranges from about 50 g/L to about 200 g/L. ### Claim 18 (depends on 15) The method set forth in claim 15, wherein the three-way-catalyst comprises a combination of platinum, palladium, and rhodium, and wherein the NH3—SCR catalyst comprises an ion-exchanged base-metal zeolite that is ion-exchanged with at least one of Na, Ba, V, Ti, W, Cu, Fe, or combinations thereof. ### Claim 19 (depends on 15) The method set forth in claim 15, wherein the oxidation catalyst further comprises a base material on which the perovskite oxide particles are washcoated, the base material comprising at least one of a zeolite, a mixture of cerium oxide and zirconium oxide, or alumina. ### Claim 20 (depends on 15) The method set forth in claim 15, wherein the oxidation catalyst does not include any platinum group metals. ### Claim 21 An exhaust aftertreatment system for removing gaseous emissions contained in an exhaust flow produced by a lean-burn that is supplied with and combusts an A/F mixture, the exhaust aftertreatment system comprising: a three-way-catalyst; an oxidation catalyst positioned downstream of the three-way-catalyst, the oxidation catalyst comprising perovskite oxide particles in an amount that ranges from about 50 g/L to about 200 g/L with the proviso that the oxidation catalyst does not include aluminium; and an ammonia-selective catalytic reduction (NH3—SCR) catalyst positioned downstream of the oxidation catalyst, the NH3—SCR catalyst being able to absorb NH3 when the A/F mixture is rich of stoichiometry and reduce NOX to N2 when the A/F mixture is lean of stoichiometry. ### Claim 22 A method comprising: providing a lean-burn spark-ignition engine that is supplied with and combusts a mixture of aft and fuel (A/F mixture) to produce an exhaust flow that comprises carbon monoxide (CO), unburned and/or partially burned hydrocarbons (HC's), and nitrogen oxides (NOX), the NOX comprising NO and NO2 in a molar ratio; delivering the exhaust flow to an exhaust aftertreatment system that comprises a three-way-catalyst, an oxidation catalyst positioned downstream of the three-way-catalyst, and a ammonia-selective catalytic reduction (NH3—SCR) catalyst positioned downstream of the oxidation catalyst, the oxidation catalyst comprising perovskite oxide particles in an amount that ranges from about 50 gl to about 200 g/L with the proviso that the oxidation catalyst does not include aluminium, and the NH3—SCR catalyst being able to absorb NH3 when the exhaust flow promotes a reducing environment and reduce NOX to N2 in the presence of NH3 absorbed by the NH3—SCR catalyst when the exhaust flow promotes an oxidizing environment; supplying the ALF mixture to the lean-burn spark-ignition engine lean of stoichiometry to promote the oxidizing environment in the exhaust flow and to oxidize CO and HC's over the three-way-catalyst, oxidize NO to NO2 over the oxidation catalyst, and reduce NOX to N2 over the NH3—SCR catalyst when the NH3—SCR catalyst comprises absorbed NH3; and cycling the A/F mixture from lean to rich to promote the reducing environment in the exhaust flow and to passively generate NH3 over the three-way-catalyst and communicate the NH3 across the oxidation catalyst and to the NH3—SCR catalyst for absorption by the NH3—SCR catalyst. ### Claim 23 A method comprising: supplying a mixture of air and fuel (A/F mixture) that is lean of stoichiometry to a lean-burn spark-ignition engine; combusting the A/F mixture that is lean of stoichiometry in the lean-burn spark-ignition engine to produce a first exhaust flow that promotes an oxidizing environment, the first exhaust flow comprising carbon monoxide (CO), unburned and/or partially burned hydrocarbons (HC's), and nitrogen oxides (NOX), the NOX comprising NO and NO2 in a molar ratio greater than about 4; delivering the first exhaust flow to a three-way-catalyst to oxidize CO and HC's; delivering the first exhaust flow to an oxidation catalyst that comprises perovskite oxide particles to oxidize NO to NO2 and decrease the molar ratio of NO to NO2 to a range of about 0.33 to about 1, the oxidation catalyst being positioned downstream of the three-way-catalyst with the proviso that the oxidation catalyst does not include aluminium; delivering the first exhaust flow to an ammonia-selective catalytic reduction (NH3—SCR) catalyst to reduce NOX to N2, the NH3—SCR catalyst comprising an amount of absorbed NH3 that reduces NOX to N2 in the oxidizing environment of the first exhaust flow, the NH3—SCR catalyst being positioned downstream of the oxidation catalyst; and replenishing the amount of absorbed NH3 in the NH3—SCR catalyst by cycling the A/F mixture from lean of stoichiometry to rich of stoichiometry to produce a second exhaust flow that promotes a reducing environment and delivering the second exhaust flow to the three-way-catalyst to passively generate NH3 for absorption by the NH3—SCR catalyst. ### Claim 24 (depends on 1) The exhaust aftertreatment system set forth in claim 1, wherein the three-way-catalyst is washcoated onto a substrate with a monolithic honeycomb structure. ### Claim 25 (depends on 24) The exhaust aftertreatment system set forth in claim 24, wherein the substrate comprises at least one of extruded cordierite, α-alumina, silicon carbide, silicon nitride, zirconia, muilite, spodumene, alumina-silica-magnesia, zirconium silicate, sillimanite, petalite, titanium, or stainless steel.