Catalytic converter

A catalytic converter is an exhaust emission control device which converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually used with internal combustion engines fueled by gasoline (petrol) or diesel, including lean-burn engines, and sometimes on kerosene heaters and stoves.

The first widespread introduction of catalytic converters was in the United States automobile market. To comply with the US Environmental Protection Agency's stricter regulation of exhaust emissions, most gasoline-powered vehicles starting with the 1975 model year are equipped with catalytic converters. These "two-way" oxidation converters combine oxygen with carbon monoxide (CO) and unburned hydrocarbons (HC) to produce carbon dioxide (CO2) and water (H2O).

"Three-way" converters, which also reduce oxides of nitrogen (NOx), were first commercialized by Volvo on the California-specification 1977 240 cars. When U.S. federal emission control regulations began requiring tight control of NOx for the 1981 model year, almost all automakers met the tighter standards with three-way catalytic converters and associated engine control systems. Oxidation-only two-way converters are still used on lean-burn engines to oxidize particulate matter and hydrocarbon emissions (including diesel engines, which typically use lean combustion), as three-way-converters require fuel-rich or stoichiometric combustion to successfully reduce NOx.

Although catalytic converters are most commonly applied to exhaust systems in automobiles, they are also used on electrical generators, forklifts, mining equipment, trucks, buses, locomotives, motorcycles, and on ships. Rarely, devices similar to catalytic converters are used in appliances such as wood stoves to control emissions.