A catalytic converter is an emissions control device that converts toxic pollutants in exhaust gas to less toxic pollutants by catalyzing a redox reaction (oxidation or reduction).

Catalytic converters are used with internal combustion engines fuelled by either petrol or diesel.

For automotive catalytic converters, the core is usually a ceramic monolith with a honeycomb structure.

Metallic foil monoliths made of Kanthal (FeCrAl) are used in applications where particularly high heat resistance is required.

The catalyst itself is most often a mix of precious metals. Platinum is the most active catalyst and is widely used, but is not suitable for all applications because of unwanted additional reactions and high cost. Palladium and rhodium are two other precious metals used. Rhodium is used as a reduction catalyst, palladium is used as an oxidation catalyst, and platinum is used both for reduction and oxidation.

Upon failure, a catalytic converter can be recycled into scrap.