It was a plot point that they needed to offer something exotic and explosive to the aliens on the other side of the weird rift, and they had a variety of explosives on stock.
But earlier in the episode, they speculated on creating the necessary rift-sealing explosion all on their own, without cooperation with the aliens - and that would have to have been more potent stuff than the materials they considered for the cooperation. On that, the dialogue went like this:
Riker: "Couldn't we replicate the elements that Tyken used?"
Data: "No, sir. We no longer have the power to reproduce complex elements in the replicator. We must find a way to generate a violent energy release without using conventional means."
So "reproducing complex elements" was a "conventional" means for our heroes. That is, they did transmutation on routine basis. But they still had explosives on stock, establishing that replication on as-needed basis was not
the preferred Starfleet approach, perhaps exactly because replicators might go down in emergencies, perhaps simply because replicators work rather slowly in producing complex bulk.