knowledge pool and phyrexian revoker used as stifle? magic

[Mint]

If there's a phyrexian revoker in the knowledge pool

other player activates some activated ability

can I respond by casting an instant, then replacing it with the phyrexian revoker from the pool, naming the card which is the source of the activated ability to counter it?

[Arix]

No. Revoker only stops the ability from being activated. Once the ability has been activated, Revoker won't do anything to stop it.