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To date, several non-SCR catalysts and catalytic systems have been suggested for NOX reduction under oxygen rich (lean) conditions, such as those which exist in diesel engine exhaust gas. However, the performance of such catalysts and catalyst systems is not clear when used on actual diesel engines. This paper reports on experimental results obtained when lean NOx catalysts are applied to diesel engine exhaust. Particularly, the catalysts' NOx performance is examined when secondary hydrocarbons are added as reducing agents directly in the exhaust gas stream. In addition, the effect of different catalyst formulations and secondary hydrocarbon addition on particulate emissions is monitored. Finally, partial system optimization is performed and the applicability of such catalysts and systems to engines operating under the US Heavy Duty Transient Cycle is examined.

The use of Pd together with Pt/Rh in automotive emission control catalytic converters is discussed. The drawbacks and advantages of Pd are explained for the conversion of CO, HC and NOx. The performance of high loaded Pd-only catalysts is demonstrated in vehicle tests according to the FTP75, ECE and Japan-10-mode procedures. It is shown that the advantageous lean HC-light-off temperature observed with high loaded Pd-only catalyst can also be reached with similar loaded Pt-only catalysts. Various alternative ways to incorporate Pd in multi-brick converters are evaluated in vehicle tests. It is shown that single brick three metal converters with high Pd-content can have advantages over conventional Pt/Rh-three way catalysts. However, the extent of the improvement depends strongly upon the particular application, and with the present trend of increasing Pd-prices these three metal converters might lead to increased precious metal costs over conventional Pt/Rh-catalysts.