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The paper describes research and development work concerning the investigation and optimization of lean NOx catalysts for gasoline and diesel engine applications. The investigations carried out in the laboratory, the engine bench and the chassis dynamometer demonstrate the influence of a number of important catalyst design parameters on the catalyst activity for nitrogen oxide reduction as well as for the conversion of carbon monoxide, gaseous hydrocarbons and in the case of diesel engine exhaust for particulates. In the first part of the paper significant improvements in catalyst activity and durability compared to the first catalyst generation are outlined. A major part of the paper deals with the influence of operation parameters such as space velocity and linear velocity of the reactants in the catalyst. Other aspects discussed are the influence of exhaust gas hydrocarbon component, active site distribution and poisoning elements affecting catalyst activity and durability.

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.