Catalyzed Particulate Filters for Mobile Diesel Applications

Catalyst coated silicon carbide filters were developed and applied for light-duty and heavy-duty diesel applications. This catalyst coating is suitable also for industrial applications and to be used on cordierite or sintered metal filters. Development activities yield solgel type coating for particulate filters with properties allowing very thin coating, containing metal oxides interacting with active sites, e.g. precious metals (Pt, Pd). A tailored catalyst composition was developed for the catalytic activity and durability in oxidation and soot regeneration reactions. The combination of thermal and catalytic particulate oxidation by oxygen and NO₂ was investigated using different regeneration strategies in engine exhaust and laboratory conditions. The passive regeneration by NO₂ initiated around 310°C with CPF only. One of the main targets was to lengthen the intervals between active regeneration phases by catalyzed particulate filters which enhance passive regeneration properties. The catalytic coating is a way to promote the active regeneration by oxidizing HC and CO emissions caused by fuel injection. The possibility to adjust filtration and pressure drop properties by coating was shown in engine bench experiments. The combination of DOC and CPF with a low Pt loading is a solution to meet future Euro 5 emission limits with NO_x calibrated engine. The replacement of platinum partly with palladium was seen as a future application to oxidize HC and CO efficiently with low NO₂ emissions.