BMW Catalytic Converters

The BMW catalytic converter (AKA catcon or cat) was first introduced in the mid-70's, and back then, it performed only two tasks, which is exactly why it was called a two-way converter. It oxidized carbon monoxide to carbon dioxide and hydrocarbons to water and carbon dioxide (oxidation stage). In 1981, the two-way converter was replaced by a much more efficient three-way catcon, which additionally reduced nitrogen oxide emissions (reduction stage).

Today, the two-way version is used in diesel applications only, while most vehicles are equipped with a three-way catalytic converter. Located between the engine and muffler, the converter actually resembles a muffler in shape, though the construction of these two units is completely different. The body of the converter is usually made of stainless steel. Inside the body, you'll find an insulated chamber, which contains three main components of any converter: substrate (or catalyst core), washcoat, and catalyst.

The catalyst core usually has a honeycomb structure, and it's most often a ceramic monolith. Basically, it serves as a support for the washcoat. The washcoat itself is a carrier for the catalytic materials. Materials for the washcoat are chosen to form an irregular surface, which maximizes the catalytically active layer available to react with the exhaust gases. And then comes the catalyst, which is most ofter a mixture of precious metals such as palladium (oxidation catalyst) and rhodium (reduction catalyst). When the exhaust stream passes through the converter, it contacts with the catalyst and all the toxic elements covert into the harmless substances. The leaving gas is monitored by the control system to make sure it meets the emissions requirements.