Not sure what you are asking here because you have not shown a Qxd4 capture. Also this is a transpositional line into the Dragon here.
Were I to see Qxd4 from White, I would play simply Nc6, forcing White to cede a tempo and giving Black a slightly better game. Nxd4 allows White to work on c6 and e6 and then Nc6 by Black is not so dangerous anymore.
So I was looking through the game explorer and I came across anti Qxd4 Sicilian move order, a common line of sicilian shown below. What I found strange was that it was ridiculously effective for black. Only three moves into the game, and black already has a slight advantage over white (from databases). It doesn't make sense to me, after all, Qxd4 isn't the main line for white (Nxd4 is). I expect this transposes into a normal sicilian dragon after a few moves, but if this is so effective for black, why is it not the main line? And why is it more effective than the main line (3... cxd4) anyways?