A third type of Lewis acid site has been recently described as Al3+ reversibly and partially extracted from the lattice using a base molecule such as ammonia.[59,60] The Al3+ cation assumes an octahedral coordination under such conditions. The reversibility is broken, however, once Al-O-Al bonds are formed, i.e., when the aluminum oxide species are completely detached from the lattice. Detailed information on such sites is not available, but it can be speculated that the drastic enhancement of catalytic activity for acid-catalyzed hydrocarbon conversion after mild steaming is associated with such reversible detached Lewis acid sites.