The catalytic converter was designed to deal with harmful pollution causing gases that are produced in the combustion chamber a vehicle's engine.
The catalytic converter turns gases such as carbon monoxide, hydrocarbons and nitrogen oxides into non-toxic emissions such as carbon dioxide and water vapour.
The toxic gases pass over the catalytic converter's chemical coated ceramic honeycomb and the resultant chemical reaction renders the gases harmless.
The catalytic converter only works at high temperatures, by mounting it near the manifold the converter heats up quickly. So when the engine is cold, noxious gases are getting through to the atmosphere until the engine warms up.
You cannot use leaded fuel with a catalytic converter as the lead coats the chemicals on the honeycomb and the gases can no longer come into contact with them, which renders it ineffective. Therefore only unleaded fuel vehicles are fitted with cats. Since the late 1980s all Australian-market cars are required by law to have them, and it's illegal to remove them.
While the catalytic converter requires no maintenance and would be expected to last the life of the vehicle with normal use, it can be damaged by impact.
http://en.wikipedia.org/wiki/Catalytic_converter
