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The second stage of the PROCONVE emission legislation, which is effective since model year 1992, was met by various of the Brazilian carmakers through the application of open loop three-way catalysts. As a result of intensive test and development programs, different open loop three-way catalyst designs were selected for ethanol and gasohol fueled vehicles, so as to reach the required emission reduction performance at optimized costs. For the ethanol fueled vehicles, the new washcoats developed allowed precious metal formulations without rhodium. The durability of these systems is supported by the properties of the fuel, since ethanol is basically free of sulphur and lead. For the gasohol fueled vehicles, a Pd/Rh formulation is applied, along with washcoats which guarantee an emission reduction performance in a broad range of A/F engine operation conditions.

The recent decision taken in the USA to further reduce the exhaust emissions from vehicles means a technological challenge for both the designers of engines as well as for the developers of catalytic exhaust aftertreatment systems. A powerful approach is the simultaneous optimization of the engine raw emissions, of the exhaust pipe and catalytic converter design and of the catalyst formulation. The paper aims at demonstrating this by means of two examples. New washcoat formulations for Platinum/Rhodium and for Palladium/Rhodium based monolithic catalysts were developed to reach both an improved conversion performance and a better durability. These catalysts were first evaluated in a model gas reactor using different hydrocarbon species, which were defined by detailed analysis of the vehicle raw emissions during the FTP-75 test cycle. The catalysts were then evaluated on an engine dynamometer, in the fresh and the engine aged state.

Two-stroke engines, which are widely used in small motorcycles, contribute considerably to the overall air pollution, especially regarding hydrocarbons (HC) and carbon monoxide (CO). Therefore countries like Switzerland, Austria and Taiwan R.O.C. have issued regulations for the control of emissions from small two-stroke engines. First, this paper surveys the emission control standards and the driving cycles for emission determination. Catalytic systems, composed of small metallic substrates and a precious metal containing three-way catalyst coating, were selected for dynamometer evaluation. Parameters influencing catalyst applications and high catalyst durability are discussed. Furthermore, an example of a catalytic reactor system already used in series production for small motorcycles to be sold in some European countries and the latest development stage for a 125 cm3 motorcycle are presented.

Fundamental research work was undertaken to elucidate the mechanism of hydrogen sulfide formation on three-way automotive exhaust catalysts during the lean to rich engine operation sequence and to identify the role of the different catalyst components in this phenomenon. Based upon this knowledge, new catalysts were developed with reduced ability to form hydrogen sulfide by minimizing the storage of sulfur oxides. Engine dynamometer tests confirmed that the suppression of the hydrogen sulfide formation was obtained without loss of catalyst activity or aging stability. The role of the catalyst's age in the hydrogen sulfide formation is discussed. The development presented shows that it is possible to avoid “scavengers” to minimize the emission of hydrogen sulfide from three-way emission control catalysts.