If coolant is blowing out of the radiator, it would seem that either the radiator has holes, or the wrong cap is in use. If blowing out of the overflow tank, a blockage in the coolant tubes. The tubes aren't crushed, are they? If the coolant does not flow, the engine will overheat. Once the coolant blows out, there are air pockets in the system, and coolant won't circulate.
It would seem that the cat issue is separate. How do you know it's burning out the cats?