As the cat & fap share a common housing on a 2.2 and it separates between them, I could clearly see the cat element. It was a ceramic block, about 5" diameter by 3", with about 200 odd straight passages through it, of maybe 1 mm diameter. On the outlet end, there was a fine metal screen of interwoven wire construction.
I examined it while replacing the flexi section of the exhaust - you could clearly see through each passage and it was obviously perfectly clear. I bashed it out anyway, thinking it probably represented a significant flow restriction even 'as new', but TBH I could tell any difference.
This is the assembly on the car.
This is the inlet end of the fap, but the cat looked similar except you could see through the holes.
complete assy, cat's inside 11, fap's inside 12
Granted my 2.2 is different....
My previous HDi 90 Xsara, had the cat replaced at about 80k to cure low power / poor response and when I got rid of it at 185k, I think it needed doing again, (or decatting). It had more turbo lag and exhaust smelt more like an non-cat diesel. If your car is getting like this, you may get a benefit, but if it's working OK, I doubt you'll notice.
May be complete coincidence, but since I decatted mine, the engine 'wobbles' at tickover, like you have a dodgy mounting, (which it hasn't). I get a lot more smoke if I use all the power and no apparent benefit. This all makes me wish I hadn't bothered.
