Catalytic converters – what is it and what is it for?

These channels are covered by a thin layer of platinum, rhodium and/or palladium, which to a large degree removes the most aggressive pollutants from exhaust fumes. Petrol engines catalytic converter deals with elimination of three basic poisons which exhaust fumes contain: carbon oxide, hydrocarbons and nitrogen oxides.

This is not so easy, however, because in fact each catalytic converter has two physicochemical devices which deal with reduction of chemical particles and their oxidation. Therefore, we should in fact refer to two catalysts contained in a catalytic converter – oxidising and reducing.

Reduction catalyst

Reduction catalyst (the first one from the engine side) uses platinum and rhodium to decompose the particles of nitrogen oxides. When a oxygen or nitrogen dioxide particle encounters platinum or rhodium, nitrogen atom is „torn apart” from it and later joins other nitrogen atoms released this way in an atmospheric particle N2.
Simultaneously, oxygen is also released in atmospheric particles O2. It is used in the other part of the catalytic converter – oxidising – to oxidise hydrocarbons particles as well as those of carbon oxide.

The effect is that in a perfect system the exhaust pipe of the vehicle releases practically only harmless substances: steam and carbon dioxide. Proper functioning of the catalytic converter depends on maintaining of optimum, stoichiometric composition of fuel-air mixture.

The most modern diesel engines are also connected with catalytic converters. Here, however, the catalytic converter takes care only of oxidising nitrogen oxides. As a completion of oxidising catalytic converter some producers assemble additionally filters of particles – i.e. of soot.

Regardless the kind of catalytic converter it must be taken into account that it is there, under the car. This device often operates at the temperature of approx. 400 degrees, therefore parking on grass or on dried leaves may lead to fire.