MTA gave the right answer about the bit. Make sure you get diamond (see his answer for what it looks like) and not tungsten carbide (pictured below).
Also make sure the bit fits on the drill, and check you have the correct adapter before leaving the shop!
Professional diamond core bits use a special screw mount to the special huge and powerful drill that is used to spin them. For 2" hole you don't need to pay extra to get that. You can spin them with a drill, but it needs torque, so it has to be a drill with a gearbox. If you use your typical hammer drill, it will spin very fast, which will be dangerous, and it won't have torque at low speed.
I use a rotary hammer drill for this, in first gear, with the hammer action set to OFF obviously! It turns nice and slow, with good torque. You need to stick a big sponge full of water inside the bit, so it gets squeezed and the water released as it bites into the material.
In fact, since you will need to make a center hole with a drill first, I'd recommend renting (or purchasing) a SDS rotary hammer drill. Then either get a diamond core bit with a SDS adapter (picture above) or a hex adapter, but your drill will need a hex chuck on top of the SDS chuck.
If the diamond bit does not have a center alignment bar poking out of it, clamp some pieces of wood on the workpiece to make a guide. You can make a triangle with 3 pieces of wood, that will hold the diamond bit cylinder in place while starting the hole.