Development of Close-Coupled Catalyst Systems for European Driving Conditions

The present paper describes the results of a joint development program focussing on a system approach to meet the proposed EURO III and IV emission standards for a passenger car equipped with a 3.2 liter, 18 valve gasoline engine. Starting with the in-production configuration of a EURO II certified vehicle (model year 1997) the following improvement points were investigated in detail.

By the introduction of a close-coupled catalyst in combination with engine measures to improve the catalyst light-off the proposed EURO III limits were met. The proposed EURO IV hurdle could be overcome by further using secondary air injection during cold-start in combination with an increased precious metal loading for the close-coupled catalyst.

In order to take care of the precious metal resources and to become more independant of precious metal price fluctuations, a new developed catalyst coating with an improved activity characteristic after high temperature aging on an engine and on a vehicle was introduced. Furthermore, the application of engine and catalyst measures are described to obtain a better catalyst durability by reducing the catalyst bed temperature during full load engine operation.

Future development work will mainly focus on the optimization of the precious metal content including an OBD-control function to monitor the catalyst activity.