Effect of sulfation methods on TiO2-SiO2 sol-gel catalyst acidity

A series of x TiO2-SiO2 (x=1.7, 4.0 and 6.7 wt.% TiO2) binary mixed oxides was prepared by a sol-gel method in acidic and basic conditions. In order to upgrade the acidic properties of the obtained solids, their sulfation was carried out in three different ways: (1) by in situ (H2SO4 was admired with the gel), (2) impregnating the dried solids with aqueous solutions of H2SO4, and (3) by impregnating as in (2) but with (NH4)(2)SO4. FTIR-pyridine adsorption and benzene deuteroexchange showed that the acid site strength depends on the sulfation method. The highest values of total acidity, determined by ammonia thermodesorption, correspond to the in situ sulfated samples. The obtained pore size distribution (4.0-5.0 nm) was narrow and the specific BET areas (250-350 m(2)/g) were large. X-Ray diffraction, RDF, XPS spectroscopy and catalytic activity in the 2-butanol dehydration show that one step sulfated in situ TiO2-SiO2 sol-gel preparations resulted in catalysts with homogeneous and strong acidity. (C) 2000 Elsevier Science B.V. All rights reserved.