What Is A Catalytic Converter?

The catalytic converter is located in the exhaust system and is designed for exhaust gases to pass through before being released to the atmosphere. The catalytic converter turns the harmful pollutants in vehicle exhaust systems into harmless gases such as steam or water vapour. When the exhaust gas comes into contact with the precious metals (or catalyst) found in the catalytic converter, a chemical reaction takes place that weakens the bonds of the polluting chemicals and allows them to easily convert into more desirable by-products of combustion.

The heart of the catalytic converter is a "ceramic monolith". This is a honeycombed structure that has many small channels through which the exhaust gases flow. The honeycomb structure means the gases touch a bigger area of catalyst at once, so they are converted more quickly and efficiently.

The entire surface of the monolith is coated with a washcoat of aluminium oxide. This enlarged surface is then coated again with the precious metals platinum and rhodium or palladium and rhodium in a ratio of 5:1. This creates reaction surfaces for oxidation, i.e. reduction, of the exhaust pollutants.

There may be several monoliths in the catalytic converter to compensate for expansion due to the high exhaust gas temperatures. The pressure-sensitive monoliths are provided with an elastic intermediate layer in a two-shell, thermally insulated stainless steel casing.

A specific operating temperature is necessary for the catalytic converter to function correctly.