Utilization of Advanced Three-Way Catalyst Formulations on Ceramic Ultra Thin Wall Substrates for Future Legislation

The LEV II and SULEV/PZEV emission standards legislated by the US EPA and the Californian ARB will require continuous reduction in the vehicles' emission over the next several years. Similar requirements are under discussion in the European Union (EU) in the EU Stage V program. These future emission standards will require a more efficient after treatment device that exhibits high activity and excellent durabilty over an extended lifetime. The present study summarizes the findings of a joint development program targeting such demanding future emission challenges, which can only be met by a close and intensive co-operation of the individual expert teams. The use of active systems, e.g. HC-adsorber or electrically heated light-off catalysts, was not considered in this study. The following parameters were investigated in detail:

• The development of a high-tech three-way catalyst technology is described being tailored for applications on ultra thin wall ceramic substrates (UTWS).
• The influence of UTWS type and precious metal loading are tested in model gas atmosphere, on an engine, and on three different vehicles with US as well as EU calibrations.
• Pressure drop controlled canning technologies were investigated to ensure the canning of UTWS like 900 cpsi/2.5 mil or 1200 cpsi/2.5 mil.

The test data indicates that improvements can be made by switching from a 600 cpsi substrate to a 900 cpsi substrate, but further only small advantages can be realized for aged systems by changing from 900 cpsi to 1200 cpsi substrates. From the performance point of view, 900 cpsi substrates seem to be the optimum. For the studies described in this paper the influence of the precious metal (PGM) loading is different for the individual applications and generally more pronounced as compared to the effect of an increased cell density - in most cases a PGM increase beyond 200 g/ft³ does not lead to major changes in the test results.