Which of the two expensive metals are used as catalysts by catalytic converters and are fitted into automobiles for reducing emission of poisonous gases?

Catalytic converter is a device incorporated in the exhaust system of a motor vehicle, containing a catalyst for converting pollutant gases into less harmful ones. In its reaction chamber, it contains a finely divided catalyst (usually platinum and other metals such as rhodium, palladium, and gold) into which exhaust gases from an automotive engine are passed together with excess air so that carbon monoxide and hydrocarbon pollutants are oxidised to carbon dioxide and water, and nitrogen oxides are reduced to nitrogen and oxygen gases.