3 Way Catalysts

Catalysts which can convert hydrocarbons, CO and NO_x in parallel are known as 3-way catalysts. They are used in all types of gasoline engines (e.g. automobiles, motorcycles, stationary engines, sport boats, small engines). 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, palladium and rhodium are deposited on oxide coatings such as alumina. The conversion of the pollutants into CO₂, water and nitrogen takes place on the precious metal particles.

A decisive factor for the effectiveness of the HeraPur^® catalyst is the right fuel-air ratio (lambda =1). If there is too much air in the exhaust (referred to as "lean exhaust"), the conversion of nitrogen oxides does not function correctly. If there is too little air available ("rich exhaust"), the catalytic combustion of the hydrocarbons and CO is incomplete. The so-called lambda probe is used to regulate the correct fuel-air ratio. If the catalyst is to work as efficiently as possible, it is necessary that it functions as soon as possible after the motor has started. This is indicated by the so-called light off temperature – from this point the catalyst is active. It also plays a role in the ageing behavior of the catalyst. As a result of deposits from motor oils and extreme temperature loadings this starting temperature drifts to higher levels; the catalyst ages.

Heraeus HeraPur^® coatings combine several advantageous properties. For one thing, special additives make Pd-rich coatings possible which perform to the required standard but at lower costs compared with Pt/Rh coatings. At the same time only the smallest quantities of precious metals are necessary, which reduces costs considerably. The precious metals are specially stabilized in order to minimize thermal and/or other ageing effects. Depending on the intended application, the compositions of our HeraPur^® coatings are adapted and tailor-made to meet the customer' s wishes. This results in efficient catalyst coatings at very attractive prices.

HeraPur^® 3 way catalysts are applied in the following fields:

Small Engines

Motorcycles

Automotive

Commercial Vehicles

Marine Applications