Catalyst materials for NOx oxidation in an exhaust aftertreatment system that uses passive ammonia SCR

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.

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.

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.

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.

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.