Acidity of zirconium oxide and sulfated ZrO2 samples

Lewis acidities of pure zirconium oxide and of two sulfated samples containing 200 or 280 μmol g-1 of sulfate, activated at 720K, have been compared by FT-IR using probe molecules such as CO, CO2 and pyridine. The sulfated samples show an increase of the strength of some Lewis acid sites. However, their number does not seem to be affected. CH3SH adsorption is very sensitive to the presence of sulfate : on pure ZrO2, it dissociates while on sulfated samples it is mainly coordinated. It is therefore deduced that sulfate formation involves the basic oxygen atoms which also facilitate the dissociation of CH3SH. The increase of the Lewis acidity observed, in the activation conditions used, is not sufficient to explain alone the superacidic properties of sulfated zirconia. © 1987.