<P> A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine to less toxic pollutants by catalyzing a redox reaction (an oxidation and a reduction reaction). Catalytic converters are used with internal combustion engines fueled by either petrol (gasoline) or diesel--including lean - burn engines as well as kerosene heaters and stoves . </P> <P> The first widespread introduction of catalytic converters was in the United States automobile market . To comply with the U.S. Environmental Protection Agency's stricter regulation of exhaust emissions, most gasoline - powered vehicles starting with the 1975 model year must be equipped with catalytic converters . These "two - way" converters combine oxygen with carbon monoxide (CO) and unburned hydrocarbons (HC) to produce carbon dioxide (CO) and water (H O). In 1981, two - way catalytic converters were rendered obsolete by "three - way" converters that also reduce oxides of nitrogen (NOx); however, two - way converters are still used for lean - burn engines . This is because three - way - converters require either rich or stoichiometric combustion to successfully reduce NOx . </P> <P> 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 and motorcycles . They are also used on some wood stoves to control emissions . This is usually in response to government regulation, either through direct environmental regulation or through health and safety regulations . A catalytic converter has to be changed every 100 000 / 120 000 km in order to be efficient . It is important to recycle this part of the car . </P>

When did catalytic converters become mandatory in us