Reduction of NOx emissions using a staged silver/alumina catalyst system
AssigneeGM Global Technology Operations LLC
InventorJong-Hwan Lee
Life of this patent
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Abstract
The hydrocarbon-assisted, selective catalytic reduction of NOx constituents in lean-bum engine exhaust is benefited by passage of the exhaust over a staged catalyst bed comprising a first stage of an alumina-supported silver catalyst for oxidation of NO to NO2 and partial oxidation of added hydrocarbon to an aldehyde. Downstream of the silver catalyst is a second catalyst selected for the reaction of hydrocarbon and aldehyde species with NO2 to reduce it to nitrogen. Gamma-alumina and BaY zeolite are examples of suitable second stage catalysts.
Claims16
A method of converting NOx content of the exhaust gas of a lean-burn engine to nitrogen where the exhaust gas comprises NO and NO2, the method comprising:
- adding a fuel-component hydrocarbon and/or a C1 to C3 alcohol to the exhaust gas;
- and
- passing the exhaust through a catalytic reactor comprising an upstream stage of a catalyst consisting essentially of silver supported on alumina and an adjacent, but separate, downstream stage of a catalyst for reduction of NO2 to nitrogen, the silver supported on alumina promoting the oxidation of NO to NO2 and the oxidation of hydrocarbon or alcohol to partially oxidized species.
A method of converting NOx content of the exhaust gas of a lean-burn engine to nitrogen where the exhaust gas comprises NO and NO2, the method comprising:
- adding a fuel-component hydrocarbon and/or a C1 to C3 alcohol to the exhaust gas;
- passing the exhaust into contact with an upstream stage of a catalyst consisting essentially of silver supported on alumina to oxidize NO to NO2 and to oxidize the hydrocarbon or alcohol to partially oxidized species comprising aldehyde species;
- and then
- passing the exhaust into contact with an adjacent, but separate, downstream stage of a catalyst for the reaction of the partially oxidized species with NO2 to reduce the NO2 to nitrogen.
A method of converting NOx content of the exhaust gas of a lean-burn engine to nitrogen where the exhaust gas comprises NO and NO2, the method comprising:
- adding a fuel-component hydrocarbon and/or a C1 to C3 alcohol to the exhaust gas;
- passing the exhaust into contact with a first catalyst consisting essentially of silver supported on alumina to oxidize NO to NO2 and to oxidize the hydrocarbon or alcohol to partially oxidized species comprising aldehyde species;
- and
- passing the exhaust into contact with a second catalyst for the reaction of the partially oxidized species with NO2 to reduce the NO2 to nitrogen, wherein the second catalyst is in a first washcoat layer applied to the cell walls of a ceramic monolith and the first catalyst is in an upper washcoat layer applied to the first washcoat layer.
Dependencies are inferred from the claim text.