Ceramic Foams as Catalyst Substrates: Pre-catalyst Application Homogenising the Exhaust Flow upstream of Aftertreatment Devices

Non-homogeneities in the exhaust line regarding flow distribution and mixing of exhaust gases upstream of catalytic converters or particulate filters are a major source of conversion efficiency reduction due to partial volume utilization.

Current supports for catalytic converters use a honeycomb monolithic substrate with only a limited potential for increased wall contacts of the gas molecules due to their laminar channel flow profile. Non homogeneities of the flow distribution at the entering cross section of the catalytic converter prevail also inside the converter channels since no momentum exchange is possible perpendicular to the main flow direction. The ceramic based foams developed and patented by Empa are a promising alternative. In the upstream of exhaust aftertreatment devices they ceramic foams redistribute the exhaust gases homogenizing the flow, enhancing turbulence and species mixing, without increasing flow resistance to prohibitive levels. Catalytically coated, they even can initiate, facilitate or even complete oxidation of unburnt HCs and CO and oxidize a substantial fraction of particulates while generating required species for the following aftertreatment step. In this paper we present some material development aspects as well as flow field investigations performed in the up and the downstream of the ceramic foams, demonstrating their potential.