Catalytic converter

A catalytic converter is an exhaust-treatment device that uses catalysts to transform pollutants from internal-combustion engines into less harmful substances.

Three-way catalyst: An automotive catalyst that oxidizes carbon monoxide and hydrocarbons while reducing nitrogen oxides. It performs all three main reactions in gasoline-engine converters.
Carbon monoxide: A colorless, odorless gas produced by incomplete combustion that impairs oxygen transport in the body. The converter oxidizes this toxic exhaust pollutant into carbon dioxide.
Gasoline direct injection: A gasoline-engine system that injects fuel directly into each cylinder rather than into the intake port. Its particulate emissions can require a gasoline particulate filter alongside the converter.
Air pollution: The presence of substances in the atmosphere at concentrations harmful to people or ecosystems. Converters reduce several major pollutants emitted by road vehicles.
Exhaust gas recirculation: An engine technique that routes some exhaust back into the intake to lower combustion temperatures and nitrogen-oxide formation. It prevents some nitrogen oxides from forming rather than treating them after combustion.
Platinum: A dense, corrosion-resistant transition metal used as a catalyst in chemical reactions. Platinum helps oxidize carbon monoxide and unburned hydrocarbons in exhaust.
Nitrogen oxides: A group of reactive nitrogen–oxygen gases formed during high-temperature combustion. These pollutants are reduced to nitrogen in a three-way converter.
Diesel oxidation catalyst: A diesel exhaust catalyst that oxidizes carbon monoxide and hydrocarbons but does not directly reduce nitrogen oxides. It handles diesel exhaust differently from a gasoline three-way converter.
Photochemical smog: Air pollution formed when sunlight drives reactions among nitrogen oxides and volatile organic compounds. Reducing vehicle nitrogen oxides and hydrocarbons helps limit the ingredients of this smog.
Diesel particulate filter: A porous exhaust filter that traps soot particles from diesel engines. It captures particles physically, unlike the converter's chemical transformation of gases.

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