| abstract |
A coated diesel exhaust filter is provided that applies a relatively low pressure drop across the exhaust system despite the buildup of soot deposits. The filter includes a porous ceramic structure having an inlet end, an outlet end, and a plurality of gas inlet and gas outlet channels disposed between the inlet and outlet ends, the channels being separated by porous ceramic walls. A catalyst is distributed at least partly within the porous ceramic walls of the structure, and is distributed at a higher concentration within portions of the ceramic walls adjacent to the outlet surfaces than within portions of the ceramic walls adjacent the inlet surfaces. Both the inlet and outlet surfaces are substantially free of the catalyst in order to maintain a gas-conducting porosity in these surfaces. The resulting filter effectively treats nitrogen oxides, carbon monoxide and unburned hydrocarbons present in the exhaust gas stream while advantageously imposing a relatively low pressure drop across the exhaust system even when soot deposits accumulate on the inlet surfaces of the ceramic walls. |