Success in this business is dependent on four factors:
- proprietary washcoat technology to meet increasing emission standards at decreasing costs
- strong customer relationships
- the ability to meet individualized OEM customer requirements through applied technology efforts during the bidding and pre-production phases
- efficient and reliable manufacturing during the mass production phase.
Structure of a catalyst
An exhaust gas catalyst consists of several components:
- the substrate
- The washcoat
- The precious metals
- The canning
Typically high temperature stable honeycomb structures are made from cordierite or metal. The cell density can vary between 200 up to 1200 cells per square inch, the wall thickness between 3 and 12 mil. The small channels are coated with one or more oxidic slurry which is either precious metal free or already contains the precious metals.
The washcoat consists of different oxide materials (Aluminium oxide providing a large high temperature stable surface; cerium components being responsible for necessary oxygen storage and release processes; stabilizers e.g. barium compounds or Zirconia-based materials). Typically these materials are used in form of slurries (35 to 45 weight % in water) and require a specific pH-value, density, particle size distribution and viscosity in order to guarantee a stable coating process.
The precious metals
In three-way catalysis Pt, Pd and Rh can be used. Typically the activity ranking is Rh > Pd > Pt and strongly depends on the aging requirements and the application on the car itself. The precious metals can either be impregnated on a washcoated substrate, or they are added to the washcoat and coated together with the washcoat. After these processing steps the catalysts are temperature treated, in most cases at around 500°C in air.
The finished part is then fixed with a special mat and is put into a so-called canning – a metal housing which is part of the exhaust pipe. The exhaust pipe further contains lambda sensors that guarantee optimum lambda window operation and thermocouple(s) that avoid overheating of the catalyst.