Zr(IV) surface chemical state and acid features of sulphated-zirconia samples

ZrO2–SO4 powders have been prepared by following either hydrothermal or sol–gel precursor preparative routes and adopting different sulphation procedures. All the samples have been calcined at the same temperature (470°C) and for the same time length (5 h), and have been characterised for phase composition (XRD) and surface area (BET). Determinations of the actual acidity pKa and density of the oxide surface sites have been obtained by a revised Hammett–Bertolacini technique. XPS analyses of the samples have been obtained by elaboration of the zirconium 3d, oxygen 1s and sulphur 2p spectral regions. XPS data are discussed in respect to the conditions of the powders preparation and cross-compared with acidity characterisations. The outcome of fitting procedures of the Zr 3d doublet of the ZrO2–SO4 powders are presented and commented in relation to the possible stoichiometry of the oxide active surface sites.