Kolmikkatalüsaatorites

Kolmikkatalüsaatorites, commonly known as three-way catalysts, are a crucial component in modern internal combustion engines, particularly in gasoline-powered vehicles. Their primary function is to reduce harmful emissions by facilitating chemical reactions that convert toxic exhaust gases into less harmful substances.

A three-way catalyst simultaneously oxidizes unburned hydrocarbons (HC) and carbon monoxide (CO), and reduces nitrogen oxides (NOx). Hydrocarbons, which are unburnt fuel, are converted into carbon dioxide (CO2) and water (H2O). Carbon monoxide, a poisonous gas, is oxidized into carbon dioxide. Nitrogen oxides, which contribute to smog and acid rain, are reduced back into nitrogen gas (N2).

The catalyst typically consists of a ceramic honeycomb structure coated with precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh). These metals act as catalytic agents, lowering the activation energy required for the chemical reactions to occur. Platinum and palladium are primarily responsible for the oxidation of HC and CO, while rhodium excels at the reduction of NOx.

For optimal performance, the air-fuel ratio of the engine must be precisely controlled, ideally close to the stoichiometric point. This precise control is achieved through feedback from oxygen sensors (lambda sensors) in the exhaust system. When the air-fuel mixture is too rich (excess fuel), there are not enough oxygen molecules for complete oxidation. Conversely, if the mixture is too lean (excess air), there isn't enough fuel to reduce the NOx effectively. The engine control unit (ECU) uses this sensor data to adjust fuel injection, ensuring the three-way catalyst operates within its most efficient window.