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Reduction of nitrogen oxides in Diesel exhaust gas is a challenging task. This paper reports results from an extensive study using Pt-based catalysts involving synthetic gas activity testing (SCAT), engine bench testing and tests on passenger cars. Preliminary SCAT work highlighted the importance of Pt-dispersion, and both SCAT and bench engine testing yielded comparable NOx conversions under steady state conditions at high HC:NOx ratios. On passenger cars in the European cycle without secondary fuel injection NOx conversion was lower than obtained in the steady state tests. Better conversion was obtained in the FTP cycle, where secondary injection was employed. Higher HC:NOx, ratios and more favourable temperature conditions which were present in the exhaust contributed to this higher conversion.

The low exhaust gas temperatures experienced on light duty Diesel vehicles present a very challenging environment for the successful operation of catalytic aftertreatment. To meet the future more severe legislation, Diesel engines are being developed with greater combustion efficiencies and advanced fueling control. These engine developments may produce lower particulate matter (PM) and nitrogen oxides (NOx) emissions, but increased hydrocarbon (HC) and carbon monoxide (CO) emissions may occur. As a result of these engine changes exhaust gas temperatures may reduce still further. These factors demand catalysts with high oxidation activity at low temperatures. This paper reviews oxidation catalyst technology developed for light duty Diesel vehicles and the factors affecting their performance. Results obtained on synthetic gas rigs, bench engines and vehicles are presented. A discussion oh the effect of the level of sulfur (S) present in Diesel fuel on aftertreatment is given.

Metal substrates have been available as catalyst supports for the past 10 years but their use has been limited to a few specialised applications, for example as light-off or starter catalysts for large cars. The emergence of Europe as an autocatalyst market with differing requirements has prompted a reassessment of the potential for metal supported catalysts. This paper will review much of the work conducted; in particular washcoat adhesion, hot-shake and high speed durability as well as reporting the results of a volume/cell density parametric study, comparing metal supported catalysts with ceramic supported catalysts on vehicles.

THE DEVELOPMENT of a novel precious metal catalyst system supported on a metal substrate is outlined. The key nature of the metallic species is demonstrated. A high performance alloy, FECRALLOY STEEL®, is identified as a suitable material. Conversion of this alloy into a durable catalyst using a proprietary pre-treatment to render it compatible with existing catalysts and production procedures is discussed. The flexibility in processing with respect to key design features e.g. cell density, is emphasised. The influence of support variables such as volume, cell density etc., on the performance of an oxidation catalyst is reported together with comparable data for ceramic supported catalyst. It is shown that at zero hours, equivalent performance, at no power loss penalty relative to ceramics, can be secured by judicious choice of cell density/volume combinations. Such equivalence can be achieved with significantly lower volumes and significant scope exists for further optimisation.