A catalytic converter is an emissions control device that reduces harmful pollutants from a car's exhaust. It converts toxic gases and pollutants into less harmful ones before they are released into the atmosphere. The converter contains precious metals like platinum, palladium, and rhodium that act as catalysts to speed up the chemical reactions that break down the pollutants. Without a catalytic converter, the car would emit harmful pollutants like carbon monoxide, nitrogen oxides, and hydrocarbons, which are harmful to human health and the environment.