Advanced Studies on Diesel Aftertreatment Catalysts for Passenger Cars

The trend towards lower exhaust gas temperatures related to the introduction of modern, highly efficient diesel engines for passenger cars in conjunction with new legislative emission regulations will require the development of amended catalyst formulations. Not only excellent performance for carbon monoxide(CO), gaseous hydrocarbons (HC) and diesel particulates is desired but also the capability to additionally reduce nitrogen oxide (NOx) under lean conditions. Generally, as for the latter a passive system, i.e. without addition of secondary fuel, is most wanted but also an active system, i.e. with hydrocarbon enrichment before catalyst, could be successful provided the penalties in fuel consumption can be kept low.

The present paper illustrates further progress in the area of diesel catalysts for passenger cars and introduces a novel washcoat formulation comprising zeolites as hydrocarbon adsorption components. By means of model gas experiments, stationary engine and chassis dynamometer tests it could be demonstrated that the utilization of zeolites boosts the removal of all major pollutants without any kind of disadvantages. The activity tests were accompanied by physical and chemical characterization methods such as specific surface area measurements (BET), transmission electron microscopy (TEM) and ion coupled plasma (ICP) analysis in order to monitor structural and chemical changes of the catalyst during aging.