It's actually over 20 years since catalytic converters where first used on cars, and here's a reason why it maybe wasn't such a good idea . .
http://www.junkscience.com/news2/catalyt.htm
//NiSk
Diesel catalytic converters
Moderator: RichardW
Although I have a small 'box' in my Xantia exhaust where a cat would be I don't think it is a cat. Am I right in assuming that a cat has a joint either side of it and is not an internal part of a long pipe and box section of exhaust? I'm rather surprised that my '97 TD is cat-less after reading the posts in the current threads.