Surface and related studies in sulphated oxides of zirconium

Zirconium oxide superacids with different sulphate ion contents were prepared from Zr(SO₄)₂ using urea as precipitating agent. These oxides were subjected to different heating temperatures. Characterization was carried out by means of infrared spectroscopy, X-ray diffraction and nitrogen adsorption studies. The surface acidity was determined by the method described by Boehm [1]. Infrared results confirmed the presence of the sulphate ions and suggested the gradual lowering through heat-treatment of the symmetry of the sulphate ions by complex formation. Surface acidity was favored when the sulphate ions were in a bidentate state of ligation. The latter ligands seemed in turn to be stabilized by water. The strongest acidity was displayed in systems where a high concentration of bidentated sulphate ions was present in conjunction with high surface areas and micropore volumes.