In an automobile's exhaust system, a catalytic converter provides an environment for a chemical reaction where unburned hydrocarbons completely combust. Hence the combustion process continues but outside the engine combustion chamber where no useful energy is extracted. Toxic car gases such as unburned hydrocarbon (UHC) and carbon monoxide (CO) would not exist if the fuel to energy conversion in the engine were perfect.
A three-way catalytic converter has three simultaneous tasks:
These three reactions are most balanced at the stoichiometric point, where there is a balanced amount of oxygen to fuel in the engine. When there is more oxygen than required, then the system is said to be running lean, and the system is in oxidizing conditions. The above two oxidizing reactions (oxidation of CO and hydrocarbons) are favoured. When there is more fuel than oxygen (stoichiometrically), then the engine is running rich. The reduction of NOx is favoured.
Catalytic converters become ineffective in the presence of lead, and the introduction of catalytic converters triggered the end of leaded gasoline.
Engineers estimate that during the last 11 years 130 million catalyticconverters used in the U.S. have eliminated automotive pollutants that-if unchecked and unabated-could have covered the country with a toxic blanket of carbon monoxide more than 500 feet deep.
Catalyticconverters typically consist of a ceramic or metal honeycombed monolith substrate that carries precious metal catalysts.
A catalyticconverter is not a stand-alone cure-all for emissions control.
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