What Is a Three-Way Catalyst?


Quick Answer

A three-way catalytic converter is an emissions-controlling device that works with a vehicle's exhaust system to reduce nitrogen oxides, carbon monoxide and hydrocarbons from the exhaust. Nitrogen oxides are the pollutants that create smog. Hydrocarbons are unburned or partially burned fuel particles. Carbon monoxide is an odorless, colorless and toxic flammable gas that is created by incomplete combustion of carbon.

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What Is a Three-Way Catalyst?
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Full Answer

Automobile engines are designed to reduce the most exhaust pollution possible by maintaining the ideal air to fuel ratio, or stoichiometric point, which is 14.7 pounds of air to 1 pound of fuel. Since automobiles cannot maintain this ratio, catalytic converters are used.

Catalytic converters are simple machines that work in two stages: the reduction catalyst and the oxidation catalyst. In the reduction catalyst stage, platinum and rhodium are used to help reduce the nitrous oxide emissions. In the oxidation catalyst stage, unburned hydrocarbons and carbon monoxide are reduced by burning them over a platinum and palladium catalyst.

Eugene Houdry invented the catalytic converter for gasoline engines in the mid-1950s. It was not until 1975 that the catalytic converter attained full-time production status, and this model only reduced the carbon monoxide and hydrocarbon emissions. The three-way catalytic converter was first used in the United States in 1981.

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