Maybe you have felt its warmth through the floor on a long trip. Catalytic converters have been standard on U.S. automobiles since the mid-1970s. The catalytic converter helped drive the push toward unleaded gasoline as well. Leaded gasoline contaminates the catalyst used inside a catalytic converter, destroying its usefulness and leading to a clogged converter. After the engine exhaust gases pass through the catalytic converter, the gases go through the muffler or mufflers, depending on the make of the automobile.
Some vehicles use a pre-converter as well, to perform a similar function.
The catalytic converter generally lasts the life of the automobile and rarely has a problem with being clogged or plugged during its lifetime. The inside of the catalytic converter is a honeycomb set of passageways or small ceramic beads coated with catalysts. A chemical reaction takes place to make the pollutants less harmful. There are many passages for the exhaust gases to flow, to allow for the maximum amount of surface area for the hot gases to pass. Nitrogen oxide is a big contributor to smog.