The most desirable type of adhesive is one that sets quickly and has some heat resistance. Mortar-based adhesives have traditionally been used for this application, but the problem is that they don’t set quickly enough to support the weight of the tiles and may require some kind of support during drying.
Cyanoacrylate superglues will often work but will be quite expensive for a large area of adhesives. I have personally used fast-curing epoxy adhesives (the so-called “5-minute” epoxies) to do this job. These adhesives set fast enough that you can hold the tiles in place by hand for a few minutes. Such tiles have been on my fireplace (initially a wood burner and later gas) for over 20 years with zero failures.