Construction and Manufacture
An important attribute of a catalytic converter is that it must provide a large
surface area so that a substantial volume of exhaust gas can come into contact with
the catalytic material, and also remain in contact long enough for the desired reactions
to occur. At the heart of every catalytic converter is a ‘substrate’, a block containing
numerous small passageways through which the exhaust gas must pass. This is the
starting point in providing the required surface area. The substrate is then coated
with a ‘washcoat’ which, after it has dried, leaves a surface which is very uneven
(at a microscopic level), the effect of this being to increase the surface area
many times. On top of the washcoat, small particles of catalytic material are deposited,
which are usually metals of the platinum group.
