| an antipollution device in an automotive exhaust system that contains a catalyst for chemically converting some pollutants in the exhaust gases, as carbon monoxide, unburned hydrocarbons, and oxides of nitrogen, into harmless compounds. |
| catalytic converter n. A reaction chamber typically containing a finely divided platinum-iridium catalyst into which exhaust gases from an automotive engine are passed together with excess air so that carbon monoxide and hydrocarbon pollutants are oxidized to carbon dioxide and water. |