Three-way catalyst function - GF49.10-P-3002-01AM

Function (schematic) 

The exhaust gases flow through the three way catalytic converter and hence come into contact with the rare metals, platinum and rhodium.

• Through oxidation, carbon monoxide (CO) is converted into carbon dioxide (CO₂ ) and hydrocarbons (HC) into water (H₂ O) + carbon dioxide (CO₂ ).
• Through reduction, nitrogen oxides (NO_x ) are converted into nitrogen (N₂ ) + carbon dioxide (CO₂ ).

The remaining oxygen content in the exhaust is a crucial factor in the conversion of pollutants. The best pollutant conversion is obtained at λ=1.

Owing to its property of being able to reduce three polluting components simultaneously, it is called a three-way catalytic converter.

Operating conditions 

As is the case for the O₂ sensor, the operating temperature also plays a very important role in the case of the catalytic converter. Appreciable conversion of the pollutants does not commence until an operating temperature of approx. 250°C.

Ideal operating conditions for high conversion rates and a long life prevail at temperatures between around 400 to 800°C.

An engine malfunction (e.g. ignition misfiring) can cause the temperature of the catalytic converters to rise above 1400°C. Such temperatures destroy the catalytic converter by melting the ceramic monolith.

Another requirement for reliable long-term operation is that only unleaded fuel be used. Lead compounds form a deposit on the active surface and as a result prevent the exhaust gases from coming into contact with the catalytic layer.