Question

Are catalysts allowed to remain in the product mixture after reaction is complete?

Answer 1

Practically,..........yes.........

Explanation:

A catalyst typically provides another lower reaction pathway, and thus increases the rate of reaction; I stress that a catalyst typically lowers `E_a`, `"the activation energy"`; it does not alter the thermodynamic parameters of the reaction.

Ideally, a catalyst is not chemically altered during a reaction. Typically, a solid metal surface (and these are the typical catalysts) can become `"poisoned"` during the chemical reaction. Catalysts, even precious metal ones, are typically discarded when this occurs. It is easier to add a new catalyst, they are so active that you do not need a large quantity and this is not an expensive proposition, than fishing out the poisoned catalyst and restoring it.