They are fitted to vehicle’s exhaust system and resemble a small muffler. Their outer body is stainless steel, while inside is a honeycombed ceramic block containing a variety of noble metals such as platinum, palladium, and rhodium. These metals cause a chemical reaction with the passing exhaust gases.
There are two types of catalytic converters
- The two-way, or oxidising, converter changes unburnt or partially burnt fuel to water and carbon dioxide.
- Three-way converters (now the most common type for petrol engines) utilise the oxidising process, and in addition, convert oxides of nitrogen into harmless nitrogen.
- Diesel engines utilise an oxidising catalyst designed specifically for diesel exhaust emissions. These don’t deal well with oxides of nitrogen emissions therefore other emission controls, such as Exhaust Gas Recirculation or Selective Catalyst Reduction are needed as well.
- Catalytic converters are sensitive to engine-related problems, such as misfires and rich fuel mixtures and can be easily destroyed by impacts with road hazards such as speed bumps. In normal service they have a long life, however, they do eventually wear out and must be replaced.
Because they typically operate at between 375°C and 600°C, vehicles fitted with them should not be parked near dry grass due the risk of fire.
Catalytic converters are an integral part of a vehicle’s emission control system and they should not be removed or tampered with.