Preparation and characterization of sulfated zirconia catalysts obtained via various procedures

Sulfated zirconia catalysts were prepared in two ways: (i) using colloidal sol-gel technique, when the peptization of Zr(OH)(4) precipitated with ammo nia from a solution of ZrOCl2 was carried out with H2SO4 or with a solution of CH3COOH and H2SO4, respectively, and by (ii) impregnation of Zr(OH)(4). Impregnation was carried out using Zr(OH)(4) as such or using precipitated Zr(OH)(4) previously heated in suspension at 90 degrees C under reflux and strong stirring. Samples obtained following the above procedures were acti vated by heating in Ar or air at 550 degrees C or 650 degrees C. Sample cha racterization was carried out using chemical analysis, N-2 adsorption-desor ption techniques, titration with propylamine in the presence of Hammet indi cators, XRD, Raman spectroscopy, pyridine and CD3CN-FTIR and XPS. In the sa mples obtained via colloidal sol-gel technique the amount of retained sulfu r was high and mono and polynucleate sulfate species as well as supported H 2SO4 were found to coexist. In such conditions, both Lewis and Bronsted aci d sites were identified and a large dispersion of acid strength was determi ned. Samples obtained via impregnation contained only a. small amount of su lfur compared with those obtained via colloidal sol-gel technique. In this case only mono and dinucleate sulfate species were found, and the acid stre ngth exhibited a rather sharp distribution. It was also found that in that case Lewis acid sites predominate. Activation in air exhibited a positive e ffect upon the increase of the acidity, irrespective of the preparation var iant, its presence "catalyzing" the nucleation of the superficial sulfate g roups. (C) 1999 Elsevier Science B.V. All rights reserved.