Characterization of sulfated zirconias by DTA-TG and drift spectroscopy

Sulfated zirconias were prepared either by impregnation of zirconia with sulfuric acid or by a one step sol gel process by using different solvents. Solids prepared under closely similar conditions in different solvents show different amounts of sulfur and surface areas, thus demonstrating that the crystallization is different. Clear differences occur in the DTA-DTG curves with the appearance of a composite peak for the sol-gel catalysts, whereas the solid obtained by the classical two-step technique shows only one peak. The number of acid sites of these samples is changed by a factor of 3 depending on the preparation. Two types of hydroxyls are observed by infrared spectroscopy: one with bands at 3640 and 3585 cm(-1), associated with protons of moderate acidity, and a second at about 3300 cm(-1) able to exchange D with C6D6. Moreover, the infrared band of sulfates also contains two components: one at 1405 cm(-1) more intense for the most acidic solids and a second one at 1380 cm(-1). After activation, these solids are as active as zeolite beta for the acylation of anisole with acetic anhydride.