Diesel Oxidation Catalysts (DOC)

Oxidation catalysts are the original type of autocatalysts and were used from the mid-1970's for petrol-engined cars until superseded by three-way catalysts. Diesel Oxidation Catalysts (DOC) remains a key technology for diesel engines where the high oxygen content of the exhaust precludes the use of three-way catalysts. Oxidation catalysts convert carbon monoxide (CO) and hydrocarbons (HC) to carbon dioxide (CO₂) and water but have little effect on nitrogen oxides (NOx). These DOCs also decrease the mass of diesel particulate emissions (but not their number) by oxidizing some of the hydrocarbons that are adsorbed onto the carbon particles. The level of particulate mass reduction is influenced in part by the percentage of Soluble Organic Fraction (SOF) in the particulate. Destruction of the SOF is important since this portion of the particulate emissions contains numerous chemical pollutants that are of particular concern to health experts. Oxidation catalysts have been retrofitted on over 750000 on-road and off-road vehicles worldwide.