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Catalysts aged under different on-road conditions were analysed with respect to their conversion of CO and HC at step changes of the synthetic exhaust gas composition. Time resolved diode laser spectroscopy and fast response FID analysis were used to characterise the catalyst response to transient changes of CO and hydrocarbons in the exhaust gas. The oxygen storage capacity was monitored at various conditions; flow rate, catalyst temperature, previous exposure to oxidizing or reducing atmosphere and amplitude of the perturbation. The technique appeared to provide a sensitive probe for analysis of the dynamic oxygen storage capacity of new and aged catalysts at exhaust like conditions. The results correlate well with the transient emission performance during vehicle tests. Further, surface characterization using SEM/EDS and XPS techniques indicated that phosphate formation was the most probable cause of deactivation.

The catalytic converter on a European diesel car must operate under extremely variable conditions, ranging from very low temperature during city-driving to high temperature during Autobahn-driving. Therefore, the development of new catalyst technology for European applications requires simultaneous achievement of properties that have long been considered incompatible. In this paper, it is shown how extremely good low temperature activity for CO and hydrocarbons (and VOF), negligible storage of sulfates, and very good thermal durability were obtained simultaneously with an appreciable reduction of NOx. Through the systematic analysis of basic catalytic phenomena, under conditions of relevance to the real-world application, it was possible to control the interaction between support, stabilizers and promoters with the precious metal package in an efficient way. The large-scale manufacturing aspects formed an important part of the development program.