catalytic thimgy

It should be fine then. Its probably the heat shield which has the hole, if it faces the floor no probs. If it faces the underbody then you need to patch it

Inside the cat it normally has 3 ceramic monoliths(basically blocks) which are honeycombed. This honeycomb is coated with precious metals(which is why old cats are usually still worth some money) and when the cat reaches running temp then a chemical reaction takes place between the metals and the exhaust gases which converts most of the harmful gases to less harmful products.