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A comparison of two different types of NOx reducing catalysts will be worked out. The potential of two De-NOx catalysts using engine out hydrocarbon emissions for NOx conversion will be shown by variation of different engine parameters. An analysis of the hydrocarbon species upstream and downstream catalyst will demonstrate, which components are responsible for the NOx reduction in the exhaust gas of a lean burn engine. By variation of different parameters during adsorbtion and regeneration phases of the adsorber catalyst the efficiency in NOx reduction will be optimized. An assessment of the suitability for lean burn engines will consider the emission reduction efficiency as well as the influence on engine fuel consumption.

Most automobile manufacturers are looking for methods to increase fuel economy. It is possible to achieve this by operating under lean conditions. The problem remains, however, that while hydrocarbon and carbon monoxide oxidation is very efficient on a 3-way catalyst in an oxidising atmosphere, reduction of oxides of nitrogen (NOx) is poor. One method to improve the efficiency for NOx reduction under lean conditions is to use a 3-way catalyst in conjunction with a NOx trap. The NOx trap stores NOx under lean conditions which is then released and reduced under rich conditions. Bench evaluations using a lean tune engine have been carried out on a number of 3-way catalysts containing a range of different NOx adsorbent components. Measurements of adsorption capacity, temperature window for lean NOx conversion and thermal durability have been made and a comparison of different adsorption materials determined. The effect of Pt loading on these parameters has also been ascertained.