XPS characterization of sulphated zirconia catalysts: The role of iron

Sulphated zirconia powders have been prepared by impregnation, with either sulphuric acid or ammonium sulphate, of hydrous precursors precipitated at room temperature. Iron-promoted samples were prepared by mixing the sulphated zirconium hydroxide with ferric nitrate solutions. Samples containing increasing amounts of iron, in the absence of sulphates, were also obtained. All the samples have been calcined at the same temperature (470 °C) and for the same length of time (5 h), and have been characterized as to phase composition (using x-ray diffraction) and surface area (using BET). The acidity features of the powders were obtained by a revised Hammett-Bertolacini technique and the sulphur and iron contents were obtained by elemental analyses. X-ray photoelectron spectroscopy analyses of the samples have been obtained by elaboration of the S 2p and Zr 3d spectral regions. The outcome of the fitting procedures of the Zr 3d doublet of the different samples is presented and commented on in relation to the possible role played by sulphates and iron in the features of the oxide active surface sites.