Ann: IonicRE Welcomes EU Critical Minerals Act Progress, page-20

Because of Northern Ireland’s conflict history, it was sensibly decided that there would be no return of a land border after the Brexit referendum. It took many years to broker a peace deal and the return of a physical land border would have been unacceptable to most people on both sides of the border.
In order for Brexit to take place, it was decided that Northern Ireland would hold a special position where it would have access to both the EU and British markets without the need for checks on goods or tariffs (and make a physical border unnecessary).
Not sure if picking Belfast was just lucky , since Ionic technologies (originally Seren) was a spin off from Queen’s university, Belfast. Or whether it was good business sense. But the fact it gives them access to both markets and, in my view, will be supported by both government bodies, makes it an excellent location.