I will show you exactly what hardware you need and how to hang or mount a tv or anything else to a block or brick wall mounting on drywall not studs.
Mount screen to brick wall.
How to install a flat screen tv on a brick wall the right fasteners.
Attaching the mount to the brick fireplace is the next step.
Using a hammer drill drill holes using the correct diameter carbide tipped masonry bit for the concrete screw diameter in use.
Concrete brick and masonry fasteners like those for drywall come in a variety of types and sizes.
Hammer it in until the lip on the end is flush against the brick wall.
Using a level determine the desired height of the display before attempting to install the wall mount.
Verify the weight of the television and choose a mount that can handle that weight.