Engine exhaust consists mainly of Nitrogen (N 2 ), however, it also contains Carbon Monoxide (CO), Carbon Dioxide (CO 2 ), Water Vapor (H 2 O), Oxygen (O 2 ), Nitrogen Oxides (NOx) and Hydrogen, as well as various, unburned Hydrocarbons (HC). Three of these exhaust components, CO, NOx and HC, are major air pollutants, so their emission to the atmosphere has to be controlled.
The catalytic converter, mounted in the engine exhaust stream, plays a major role in the emission control system. The converter works as a gas reactor and it's catalytic function is to speed up the heat producing chemical reaction between the exhaust gas components in order to reduce the air pollutants in the engine exhaust. The catalyst material, contained inside the converter, is made of a ceramic substrate that is coated with a high surface area alumina and impregnated with catalytically active, precious metals.