An emissions control device that is part of the exhaust system. Its purpose is to reduce harmful tailpipe emissions caused by the engine. The catalytic converter lowers exhaust emissions by creating a catalysis (chemical reaction) within itself. Here is how it works: Hot exhaust gas flows through the converter, which is filled with sulfur or platinum balls. The sulfur or platinum heats up to combustion temperatures, thus burning any unburned gases that might be in the exhaust flow, reducing tailpipe emissions.