| abstract |
A NOx trapping filter is provided for use in emission control systems, for example, on the exhaust gas from an internal combustion engine. The NOx trapping filter has a substrate constructed using bonded fiber structures, which cooperate to form a highly uniform open cell network, as well as to provide a uniform arrangement of pores. The substrate typically is provided as a wall-flow honeycomb structure, and in one example, is manufactured using an extrusion process. In this way, the substrate has many channel walls, each having an inlet surface and an outlet surface. The inlet surface has a uniform arrangement of pores that form a soot capture zone, where soot and other particulate matter is captured from an exhaust gas. A NOx adsorber material is disposed in the filter to trap NOx during lean operation of the engine. A NOx conversion catalyst is also disposed inside the channel wall, where NOx and excess hydrocarbons in the exhaust gas are reacted to less harmful substances when the engine system is operated in a rich condition. Because of the uniform pore structure and open cell arrangement inside the channel wall, the filter is capable of being heavily loaded with catalyst, adsorber, while avoiding undue increase in backpressure to the internal combustion engine. |