Question

Are catalysts ever permanently changed in a reaction?

Answer 1

Ideally no, but when has chemistry ever been ideal?

Explanation:

Catalysts are often said to be `"poisoned"` in a chemical reaction. That is after a time of operation they will become ineffective. Heterogeneous catalysis is often inactivated by the addition of mercury metal, which saturates the catalytic surface.

With industrial operations, most of the time, catalysts are so active, that a little new stuff can be added periodically. Catalysts are so active that this can often be performed even if the catalyst is a high-value metal: the catalyst loading can be so low as to allow consideration of the cost of the catalyst to be trivial.