An Optimal Usage of Nox in a Combined Pt/Ceramic Foam and a Wall-Flow Monolith Filter for an Effective Nox-Assisted Diesel Soot Oxidation

For the NO_x-assisted diesel soot abatement, the trend of decreasing engine-out NO_x emission will become a serious threat unless NO_x can effectively be utilised. A filter candidate consisting of Pt-containing ceramic foam and a wall-flow monolith configuration (an optimised catalytic filter) is proposed to employ an optimal usage of NO_x. By design this configuration is capable to employ two stages of filtration, namely: deep bed filtration on the foam and surface filtration on the wall-flow monolith. At the same time, two modes of soot oxidation reactions will operate. In Pt/ceramic foam multiple NO oxidation to NO₂ and trapped diesel soot oxidation by NO₂ take place, while part of NO₂ is released as NO₂-slip and this NO₂-slip is subsequently utilised to oxidise trapped soot on a wall-flow monolith. In laboratory tests, this concept is clearly demonstrated that it outperforms the activity of conventional regenerating trap, based on upstream NO-NO₂ conversion.