Oxidation Catalysts

Oxidation catalysts are mainly used in diesel engines for the reduction of pollutant emissions. For the manufacture of catalysts, shaped bodies (known as monoliths) are coated with layers containing precious metals. For this, finely distributed particles of the precious metals platinum and palladium are deposited on oxide coatings such as alumina. The conversion of the pollutants into CO₂ and water takes place on the precious metal particles. Platinum and palladium are deposited in a fine distribution over high surface area oxides such as alumina.

In contrast to the 3-way principle, there is a surplus of air in diesel exhaust gas, referred to as lean exhaust. This means that NO_x cannot be converted to nitrogen on an oxidation catalyst. Instead, at temperatures of 150 - 400°C, NO is oxidized to NO₂. One takes advantage of this reaction in, for example, the regeneration of particle filters (see soot filters). Furthermore, the exhaust of a diesel engine is generally considerably cooler than that of a gasoline engine. This means that the working temperature of the catalyst has greater significance in the oxidation catalyst, for the catalyst only becomes active above a certain temperature. Frequent changes in temperature and deposits of engine oil and fuel additives push this working temperature to higher levels and the catalyst ages.

HeraPur^® catalyst coatings for oxidation catalysts permit a low working temperature with good resistance to ageing. With our special expertise a low precious metal loading is achieved. Furthermore the more economical palladium can be substituted for the expensive platinum which results in a cost saving. This has no influence on the performance of the catalyst.

Depending on the design of the coating, the oxidation of the NO can be increased or also almost completely suppressed. This makes it possible to design application-specific catalysts to customer requirements.

HeraPur^® oxidation catalysts are applied in the following fields:

Small Engines

Motorcycles

Automotive

Commercial Vehicles

Marine Applications