That is the EGR feed pipe. Worst case you may have to replace the pipe if it is too seized to be removed with a line wrench crows foot and a breaker bar.
You have to be careful when applying heat because of the aluminum manifold, but heating should allow it to loosen. If that doesn't work then you will have to cut the pipe to allow for a socket to used and you will then be able to remove the fitting and the piece of the pipe seized inside it as a single piece.
Answers
You have to be careful when applying heat because of the aluminum manifold, but heating should allow it to loosen. If that doesn't work then you will have to cut the pipe to allow for a socket to used and you will then be able to remove the fitting and the piece of the pipe seized inside it as a single piece.