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Catalyzed diesel particulate filter systems have now been successfully introduced and implemented in Europe. In the meantime, automotive manufacturers are working on the second generation of catalytic filters with the aim of reducing the overall system costs. In particular savings in precious metal costs are focussed by the use of highly-active catalysts which are stable at high temperatures. A possible approach here is the implementation of oxidation catalysts and catalytically coated filters based on platinum and palladium. In this context, the functio-nality of platinum/palladium-based, catalyzed filters was investigated by numerous measurements on a synthetic gas and an engine bench as well as by vehicle tests on a roller dynamometer. The HC/CO oxidation activity, the poisoning resistance towards sulfur and the desulfurization capability, the exothermic behaviour due to the conversion of subsequently injected hydrocarbons and the NO2 formation potential were examined in detail.

This paper describes the function and application of the preoxidation, hydrolysis and SCR catalysts individually and as a combined system for urea SCR both in model gas and engine bench tests. Using the basic system and a non-optimized urea injection strategy 45% NOx conversion was achieved in the ESC engine test. Adding a preoxidation catalyst significantly improved the NOx conversion in the low temperature region of the engine mapping. NOx conversions over 75% can be achieved in the ESC test using this improved system. With a 50% reduced SCR catalyst volume still a NOx conversion of over 65% could be achieved. Tests after 200 hours engine aging show that the activity of the system is stable.

Several diesel passenger car manufacturers in the European Union recently announced the future use of catalyzed diesel particulate filter systems on their vehicles. The major technical challenge is the periodical regeneration of the filters loaded with the retained diesel particulates. In order to promote filter regeneration, catalytic activation of the accumulated soot is advantageous. Therefore, the first serial application of diesel particulate filter systems uses catalytically active fuel additives. These systems were introduced about four years ago. Since that time, other systems, using a dedicated catalytically activated diesel particulate filter combined with an upstream diesel oxidation catalyst, have been introduced as well. This allows filter regeneration without extra fuel additives. In the past, adding catalytic coating to a filter substrate has often resulted in increasing the pressure drop over the filter to an unacceptable level.