catalytic converter

Device attached to the exhaust system of an auto or other engine to eliminate or substantially reduce polluting emissions. It converts three harmful substances into harmless ones: carbon monoxide (a poisonous gas) into carbon dioxide, nitrogen oxides (cause acid rain and smog) into nitrogen and oxygen, and hydrocarbons (cause smog and respiratory problems) into carbon dioxide and water. Catalytic converters consist of a stainless steel box attached to the muffler and containing ceramic beads or honeycomb coated with catalysts (usually alumina, ceria, and other compounds combined with palladium, platinum, and rhodium) and various sensors that regulate the fuel and air passing through the engine.