Catalytic Converter

Catalytic Converter, device incorporated in the exhaust system of motor cars and other vehicles that reduces emissions of certain pollutants. Exhaust gases are passed through chambers coated in such rare metals as palladium and platinum; these metals act as catalysts, encouraging chemical reactions that change such pollutants as carbon monoxide, nitrogen oxides, and certain hydrocarbons into carbon dioxide and water. Emission standards made catalytic converters mandatory for new petrol-engine cars sold in the United States since 1983 and in the EU since 1993. Recently, catalytic converters for diesel engines have also been developed.

In practice catalytic converters reduce emissions less than in test conditions. They can take an 8-km (5-mi) drive to become effective and require the vehicle to use unleaded petrol, since lead causes them to cease functioning. They increase fuel consumption, and there is concern regarding the environmental impact of obtaining and disposing of the rare metals they contain.