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A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually used with internal combustion engines fueled by gasoline or diesel. The function of a catalytic converter filters out harmful byproducts in the exhaust gases and burns them up. And while the main function of a catalytic converter is to reduce harmful emissions, it also improves your car’s efficiency.
When exhaust gases pass through a heated catalytic converter, two catalytic events (chemical reactions) take place:
1. The reduction catalyst is the first of the two catalytic events to occur. It uses the metal catalysts to reduce harmful nitrogen oxides by separating the molecules into nitrogen and oxygen. The nitrogen is trapped within the converter, while the oxygen passes through.
2. The oxidation catalyst is the second catalytic event. It reduces unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over the metal catalyst.
The Catalytic converters require a temperature of 400 °C (752 °F) to operate effectively. Therefore, they are placed as close to the engine as possible, or one or more smaller catalytic converters (known as "pre-cats") are placed immediately after the exhaust manifold. Vehicles fitted with catalytic converters emit most of their total pollution during the first five minutes of engine operation; for example, before the catalytic converter has warmed up sufficiently to be fully effective.
Two-way
A 2-way catalytic converter has two simultaneous tasks:
This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. They were also used on gasoline engines in American- and Canadian-market automobiles until 1981. Because of their inability to control oxides of nitrogen, they were superseded by three-way converters.
Three-way
Three-way catalytic converters have the additional advantage of controlling the emission of nitric oxide (NO) and nitrogen dioxide (NO2) (both together abbreviated with NOx and not to be confused with nitrous oxide (N2O)). NOx species are precursors to acid rain and smog.
"three-way" (oxidation-reduction) catalytic converters have been used in vehicle emission control systems in the United States and Canada; many other countries have also adopted stringent vehicle emission regulations that in effect require three-way converters on gasoline-powered vehicles. The reduction and oxidation catalysts are typically contained in a common housing.
Many vehicles have a close-coupled catalytic converter located near the engine's exhaust manifold. The converter heats up quickly, due to its exposure to the very hot exhaust gases, enabling it to reduce undesirable emissions during the engine warm-up period. This is achieved by burning off the excess hydrocarbons which result from the extra-rich mixture required for a cold start.
Warm-up period
Vehicles fitted with catalytic converters emit most of their total pollution during the first five minutes of engine operation; for example, before the catalytic converter has warmed up sufficiently to be fully effective
Caution should be considered if your automobile is parked in a grassy environment, as brush fires are often caused, when the long dry grass is ignited by the extreme heat from the converter.
A well-maintained car will extend the life of your catalytic converter, minimizing the possibility of a costly catalytic converter repair or replacement.
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