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An overview is given on the state of the art of a new catalytic exhaust gas aftertreatment device for diesel engines. The function of a precious metal based, flow-through type diesel oxidation catalyst is explained. Much attention is paid to the durability of the diesel oxidation catalyst and especially to the influence of poisoning elements on the catalytic activity. Detailed data on the interaction of poisoning elements such as sulfur, zinc and phosphorus with the catalytic active sites are given. Finally it is demonstrated that it is possible to meet the stringent emission standards for diesel passenger cars in Europe with a new catalyst generation over 80.000 km AMA aging.

Stringent standards for the emission of particulate matter by heavy duty diesel engines will come into effect in the nineties in the US and are anticipated to come into effect in the same period in W-Europe and in Japan. This has lead most of the manufacturers to intensify the evaluation of exhaust aftertreatment devices. Although particulate filtering systems proved to be valuable in limited fleet applications, the general introduction did not take place because of complicated and limited durability regeneration. Flow-through catalysts which were introduced for passenger cars in 1989 drew a lot of attention for potential heavy duty diesel applications. In this paper the major parameters affecting the performance of these flow-through catalysts and the particularities related to heavy duty diesel application are outlined. The parameters deal with the fuel sulfur content, the test cycles applied, the catalyst formulation and washcoat composition.

Future emission standards for passenger cars are mainly aiming at a stringent reduction of their hydrocarbon (HC) emissions. A key factor to meet these requirements for passenger cars with otto engines and closed-loop three-way catalyst is the improvement of the cold-start behavior of the aftertreatment device. Amongst other concepts HC-adsorber systems have been proposed to cope with this problem. In the present paper, results of a fundamental research program on these molecular sieve adsorber systems are discussed. Model gas reactor experiments were used to select raw materials for hydrocarbon-adsorption capacity. The materials of choice were used either alone or in combination with state-of-the-art three-way catalysts; the performance of these systems was evaluated on two different vehicles according to the FTP 75 cycle. To get quantitative information about the nature of the stored HC, all investigations were supported by a detailed gas chromatographic HC-analysis.