TG DTA, XRD AND NH3-TPD CHARACTERIZATION OF LAYERED VOPO4-CENTER-DOT-2H(2)O AND ITS FE3+-SUBSTITUTED COMPOUND/

Iron(III)-substituted vanadyl phosphate, [Fe(H2O)](0.20)VO0.80PO4. 2.2 5H(2)O (FeVOP), has been prepared and characterized by XRD and TG/DTA analyses. The new compound is isomorphous with layered tetragonal VOPO 4. 2H(2)O (VOP), but it possesses a lower interlayer distance. Informa tion on the reactivity and surface acidity of both VOP and FeVOP has b een obtained by NH3-TPD experiments. The hydrated materials adsorb hig h amounts of NH3 (up to 2 mmol g(-1)). Different ammonia-containing ph ases are formed, characterized by lower interlayer distances in compar ison with the NH3-free parent compounds. NH3 is intercalated between t he layers without displacement of water. The materials dehydrated by h eat treatment at 450 degrees C retain the layered structure but adsorb NH3 only on the external surface. A wide variety of acid sites, from weak to strong, was observed. A mechanism is proposed for the NH3- aci d sites interaction. SEM micrographs of VOP and FeVOP are shown.