The role of the oxide precursor on the features of sulphated zirconia

Zirconia samples have been obtained by calcining, at 470 degrees C, hydrous precursors prepared by following two different procedures: (a) room temperature precipitation by NH(3), at acid pH (less than or equal to 2.5) followed by 96 h refluxing; (b) neutralisation (pH =7.0-7.5) of ZrCl(4) solutions at the boiling point by KOH. The oxides, calcined starting from the two precursors, appear to be composed either of monoclinic or tetragonal (metastable) ZrO(2). Sulphated zirconia samples have been obtained by treating the precursor powders with sulphuric acid at different concentrations and subsequently calcining them at 470 degrees C. The sulphate-doped oxides have been characterised for phase composition-crystallinity (XRD), water-sulphur content (TGA, elemental analysis), surface area (BET) and surface chemical state (XPS also in combination with ion sputtering). The different oxide precursors produce distinctive features, on the treated oxides, concerning specifically the degree of hydration/hydrophilicity of the samples and the nature of the zirconium surface sites. (C) 1998 Elsevier Science B.V.