There is a major contradiction in your question that limits my answer.
" the ignition and injection system cannot be the problem" & "The ignition and injection systems are perfect "
I call this the "Engine Management System" as they are both connected and overlap and sometimes difficult to separate. What ever you call it, if they "can not be the problem" and are "perfect". That eliminates the possibility that any of the "sesnsors" are failed as they are trickle parts of the "system". An Oxygen Sensor, Mass Air Flow sensor, Coolant Temperature Sensor, etc. are all part of the "engine management system" and the failure of any one these sensors would constitute that the engine management system was NOT "perfect" or "not the problem".
If you want to eliminate sensors from the system and not include them, yes, there are a number of possibilities that could cause the system to run rich and possibly damage the catalyst provided the operator ignored the illuminated MIL and continued to operate the vehicle even though the On Board Diagnostics illuminated the MIL indicating there was a "problem in the system". I hope you can see where I am having a problem with the question as it has been posed. C.O. will not damage the catalyst. HC (unburned fuel) is the leading cause of catalyst damage (overheated).
Problems that could cause high levels of HC;
- Misfire - Due to ignition coil, spark plug, dirty/leaking/failed injector, vacuum leak to the point of misfire, wiring, failed ECM
- Upstream Oxygen sensor reporting VERY lean
- MAF sensor grossly over reporting
- CTS (Coolant Temperature Sensor G62) reporting much colder than actual temperature
- Very high fuel pressure - likely failed regulator or restricted return
- Restricted Intake system
- Restricted exhaust system
- Air leak into the exhaust upstream of the upstream Oxygen sensor
- A fuel saturated carbon canister
- A improperly functioning purge system
- Incorrect, poor quality, or contaminated fuel in the fuel tank
Nearly all of these possibilities would illuminate the MIL and likely even cause the MIL to flash before irreparable catalyst damage would result. On board diagnostics is an important part of the engine management system and ignoring the illuminated MIL would be a key factor in the failure of the catalyst.
I hope this answers your question. If not possibly you could word it in such a way that I could give you an academically accurate and correct answer.
Please rate my answer as OK, GOOD, or EXCELLENT. With a lower rating I will not be compensated. Please contact me with your concerns if you cannot rate my answer OK, GOOD or EXCELLENT.