An air pollution control device using the exhaust system of cars. The converter helps complete combustion of any fuel that was not burned in the engine and reduce the presence of other harmful emission concentrations. The converter changes the unburned hydrocarbons and carbon monoxide in the exhaust into carbon dioxide and water vapor. The converter use chemical catalysis to create this change.
[Fleisher, Paul. Ecology A to Z. Dillon Press, New York. 1994. p. 38.]
Source: Atmospheric Chemistry Glossary