Abstract: Structural changes in the SO₄^2-,/ZrO₂ superacid system caused by desorption of preadsorbed water and pyridine were studied with IRspectroscopy.The experimental observations show that SObonds in the surface sulfur species of the hydrated samples exist in two forms, i, e., the ionic SObond (Ⅰ) and the covalent SOdouble bond(Ⅱ).Ⅰ transforms into Ⅱ with the removal of water from the sample.The presence of two types of SObonds and the transformation from Ⅰ to Ⅱ were also observed in samples preadsorbed with pyridine.In addition, the asymmetric stretching frequency of SObond Ⅱ shifts to a higher frequency during desorption of preadsorbed water or pyridine, suggesting that the bond order and the double-bond character of the SObond are increased.It is found that only Lacid sites are present on the surface of the carefully dried SO₄^2-/ZrO₂ sample.After adsorbing water, some Lacid sites may transform into Bacid sites in the ratio of 1:1.However, the number of Lacid sites in the sample is always higer than that of Bacid sites.The structure of the Bacid sites formed after hydration has been discussed by using the results of changes in bond order, bond length and partial charge on oxygen.

Key words: SO₄^2-/ZrO₂ system, Superacid, L acid, B acid.Structure