TWC Catalyst Design: Monoliths
Monolithic honeycombs are used
in the place of pellets. The most
common cell structure used has
62 cells/cm2 with a 0.152 mm
thick wall to give a bulk
density of 0.4 g/cm3.
The ceramic has a relatively
low surface area for catalysis,
and a “washcoat” in the form of an
aqueous suspension of alumina and
other components is applied and fixed by calination.
The washcoat provides a means of dispersing precious metals to a high degree, while reducing coalescence sintering and acting as a sink for poisons. These proprietary application procedures are highly evolved.