What kind of thinset should I use on porcelain?
If the tile maker does not have a suggestion (they often do - see if they have a website if there's nothing in or on the package) any thinset and a notched trowel somewhere between 1/8x1/8x1/8 and 1/4x1/4x1/4 (depending on floor flatness) should do. Concrete is an excellent tile substrate (does not tend to move or flex) so there's no need for special acrylic modified flexible thinset.