Inside a Catalytic 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.

The catalysts include:

  • Oxidation catalysts: Palladium (Pd) and platinum (Pt) metals in very small amounts (to keep the catalytic converter price down) convert the hydrocarbons of unburned gasoline and carbon monoxide to carbon dioxide and water.
  • Reduction catalysts: Palladium and rhodium (Rh) metals also in very small amounts convert the nitrogen oxide to nitrogen and oxygen. Nitrogen oxide is a big contributor to smog.

Many states and localities have legislated annual automobile emissions testing that checks the actual emissions content. The exhaust emissions test checks for the absence of a converter or a malfunctioning one during an inspection. It's illegal in some states and localities to remove a factory-installed catalytic converter. A mechanic can sometimes temporarily remove it and replace the catalytic converter with a test pipe, but the rules on this can vary from place to place.

So how do you know for sure if your catalytic converter has failed? Get the answer on the next page.