The dynamic behavior of the ethanol adsorption on g-alumina were investigated at 180 and 200 DegC by the transient-response method coupled with FT-IR data of the catalyst surface. The existence of three adsorbates was demonstrated: a reacting species which is the precursor for the formation of the gas-phase ethene; an inhibiting species responsible for the low steady-state reaction rate; and a spectator species accumulating on the catalyst surface. Their IR spectra indicate an ethoxide-like structure for the three adsorbates. Their C-H stretching bands can be depicted by four Lorentzians whose parameters indicate different surface environments. The surface concn. of the reacting species was detd. on the basis of the transient ethene response. A value of 0.77+-0.07 mol/kgcat was found at 180 DegC. The surface concn. of the spectator species was detd. by ex-situ thermogravimetric expts. A value of 0.13+-0.01 mol/kgcat was found at 180 DegC. The most likely structure of this species corresponded to an ethanol mol. coordinated in a bidentate manner on Al3+ cations, with stabilization of the alc.-hydroxyl group via lateral hydrogen bonding with an adjacent surface hydroxyl. [on SciFinder (R)]