They are used in stoichiometric applications and assisted by electronic fuel management systems to reduce the level of harmful CO and NOx emissions.
The operation is carried out thanks to some catalysing substances (platinum, rhodium and other) present inside the component to chemically transform the harmful gases into less harmful or harmless gases, and at the same time working an oxidation process for the combustion of the monoxide carbon (turning it into carbon dioxide) thanks to the release of oxygen molecules from chemical reactions.
They are used in poor-mix applications by inserting the exhaust gases in an oxidizing environment at temperatures between 300 and 700 degrees to make the transformation of the polluting elements into harmless or less polluting elements (for example CO in CO2).
The exhaust gases of internal combustion engines mainly produce innocuous gases, normally present in the atmosphere and in a less polluting gases of various types, varying according to the fuel used:
Under optimal conditions, catalytic converters can achieve very high efficiencies with a reduction of 90% of pollutants. To achieve this result, however, the stoichiometric ratio must be as exact as possible with the need for continuous electronic control of the right air / fuel ratio. It is also necessary that the fuels used are free of ‘poisonous’ elements (phosphorus, sulfur, iron, lead and others) able to bind to the catalyzing elements, inhibiting and neutralizing their effect. Finally, for a correct functioning, and to make the catalysts operative in particular in the oxidation processes, an operating temperature of between 300 and 700 degrees is required, possibly using electric heating systems in cold starts, for a quick reaching of the temperature of ‘light off’ (about 300 °).