I can make a stab at it in Texas terms..
I have seen two kinds one is full of catalyst beads and the other has the catalyst formed in sort of a mesh or web inside the steel container,
What happens is the catalyst gets hot as the exhaust passes through it and eats (burns again?) the stuff it is intended to get rid of that is in the exhaust..
When you get foreign matter or too much fuel in the catylist, or even after the intended amount of time.. The catylist grows shut and disallows ehhaust to pass through.. Then it is time for another converter..
Sunder will prolly get on here and give all the technical names and stuff later..
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />