The lethal components of exhaust gas are rendered harmless by the converter. This device should remain effective virtually forever unless it's damaged. Its enemy number one originally was the lead in gasoline. Culprits four and five are leaking fuel injectors and ignition misfire, such as one or more worn spark plugs. Finally, and not necessarily least common, is oil burning due to worn engine components.
Oily exhaust can ruin a catalytic converter.
Car Care Council points out that even the most advanced vehicle design still demands periodic and maintenance service.