S. Melada et al., Physico-chemical features and catalytic activity of sulfated zirconia prepared by sol-gel method. The role of the solvent evaporation step, CATAL LETT, 75(3-4), 2001, pp. 199-204
ZrO2-SO4 powders have been prepared by following a single-step sol-gel prep
arative route using zirconium propoxide as the starting compound. Sulfuric
acid was employed both as the sulfating agent and as the catalyst of the po
lycondensation reaction in the gel formation. Two different series of dried
precursors were obtained by either evaporating the solvent in an oven at 1
00 degreesC (xerogels) or in supercritical conditions (aerogels). All the s
amples were calcined at three temperatures (470, 550, and 630 degreesC) for
the same time length (5 h). The powders were characterized for phase compo
sition-crystallinity, surface area-porosity, sulfur content and surface sta
te (XPS). The catalytic activity of the calcined samples was tested in the
isomerization of n-butane in a continuous system at 150 degreesC in absence
of H-2 and 250 degreesC in presence of H-2. The role played by the conditi
ons of the solvent elimination, at the end of the sol-gel reaction, in affe
cting the physicochemical and catalytic properties of the powders is discus
sed.