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AssigneeJohnson Matthey Public Limited Company
InventorsAndrew Chiffey, Paul Phillips
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An exhaust system for an internal combustion engine has a catalysed ceramic wall flow particulate filter coated with a washcoat composition. The washcoat composition includes an oxidation catalyst of at least one platinum group metal and a NOx absorbent. The washcoat composition has a D50 of less than or equal to 8 μm. The NOx absorbent absorbs NOx contained in an exhaust gas when the composition of the exhaust gas is lambda >1, and releases the NOx absorbed in the NOx absorbent when the exhaust gas composition is 1≦lambda. The exhaust system has a platinum group metal catalyst upstream of the filter for oxidising NO to NO2 at least when the composition of the exhaust gas is lambda >1. The uncoated portions of the ceramic wall flow particulate filter have a porosity of >40% and a mean pore size of 8-25 μm.
An exhaust system for an internal combustion engine, which system comprising a catalysed ceramic wall flow particulate filter coated with a washcoat composition comprising an oxidation catalyst comprising a platinum group metal selected from the group consisting of platinum, palladium, and a mixture thereof, and a NOx absorbent comprising a metal selected from the group consisting of an alkali metal, an alkaline earth metal, a rare earth metal, and a mixture thereof contained in an exhaust gas when the composition of the exhaust gas is lambda >1, and for releasing the NOx absorbed in the NOx absorbent when the exhaust gas composition is 1>lambda, and a platinum group metal catalyst upstream of the filter for oxidising NO to NO2 at least when the composition of the exhaust gas is lambda >1, wherein the uncoated ceramic wall flow particulate filter has a porosity of >40% and a mean pore size of 8-25 μm and the washcoat composition has a D50 less than or equal to 8 μm.
A method of treating an exhaust gas of an internal combustion engine, which method comprising oxidising NO in the exhaust gas to NO2 at least when the composition of the exhaust gas is lambda >1, trapping particulate on a catalysed ceramic wall flow filter coated with a washcoat including a NOx absorbent, oxidising NO to NO2 on the filter when the composition of the exhaust gas is lambda >1, absorbing the NO2 in the NOx absorbent when the composition of the exhaust gas is lambda >1, releasing the absorbed NOx as NO2 when the exhaust gas composition is 1≧lambda and combusting particulate trapped on the filter in NO2, wherein the step of oxidising NO to NO2 is performed upstream of the filter, the uncoated ceramic wall flow particulate filter has a porosity of >40% and a mean pore size of 8-25 μm, and wherein the washcoat composition has a D50 less than or equal to 8 μm.
Dependencies are inferred from the claim text.