The three-way catalytic converter currently permits the most efficient, safest and most reliable form of emission control in petrol engines. As the name implies, the three-way catalytic converter converts three pollutants: hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) into less harmful gases.
The catalyst consists of a metallic or ceramic support material with a coating of noble metal (platinum, rhodium, iridium). The catalyst converts about 90% of the pollutants into carbon dioxide (CO2), nitrogen (N2) and water (H2O). To do its job effectively, the three-way catalytic converter requires a certain working temperature. This is why close-coupled preconverters are often used to reduce harmful emissions as early as the stage when the engine is warming up.
The optimum composition for the conversion of the petrol-air mixture is regulated by the lambda sensor in conjunction with the engine control unit.