Johnson Matthey - Cars, Vans and Light Trucks

The catalyst sits in the exhaust system, either near to the engine (close-coupled), or further down the tailpipe (underfloor). Harmful gases are converted to harmless products in a reaction with the precious metal-containing catalyst.

Gasoline or petrol fuelled vehicles typically use a 3-way catalyst, so-called because it converts 3 pollutants, carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx) to carbon dioxide, water and nitrogen. Conversion rates of over 90% are possible.

Diesel engines require a diesel oxidation catalyst (DOC) to remove CO and HC and can also reduce particulate matter (PM) by up to 50%. More effective PM removal is achieved with diesel particulate filter (DPF) systems.