Free radical formation in ZrO2-SiO2 sol-gel derived catalysts

Zirconia-silica mixed oxides have been prepared by the sol-gel method using zirconium butoxide and tetraethoxysilane as starting materials. The sample s were sulfated using sulfuric acid as alkoxide hydrolysis catalyst or by i mpregnation with sulfuric acid of a sample previously prepared using HCI as alkoxide hydrolysis catalyst. In thermally treated samples, an intense EPR signal was observed for the sample prepared using HCI, while the EPR signa l was lower in the sulfated samples. FTIR-pyridine adsorption spectra showe d that Bronsted and Lewis acidity is developed in the sulfated samples, The formation of two types of Bronsted sites depending upon the sulfating meth od used is proposed, The catalytic activity of the samples was evaluated in isopropanol and n-butanol dehydration. The mechanism by which sulfation is achieved and the Bronsted-type site formed are discussed. (C) 1999 Academi c Press.