M. Valigi et al., Ionic size and metal uptake of chromium(VI), molybdenum(VI), and tungsten(VI) species on ZrO2-based catalyst precursors, J PHYS CH B, 103(51), 1999, pp. 11318-11326
Zirconium-supported Me(VI) oxide (Me = Cr, Mo, W) was prepared by the equil
ibrium adsorption method at pH values 2 and 8 by using as a support either
hydrous [ZrO2(383)] or thermally pretreated zirconium oxide [ZrO2(T)]. The
prepared solids were characterized by X-ray photoelectron spectroscopy, sur
face area determinations, electron scanning microscopy and analytical metho
ds. Samples of definite grain size ranges of ZrO2(383) were also compared.
The results show that the W-containing samples based on ZrO2(383) differed
from Cr- and Mo-samples in the uptake dependence on pH. Despite its higher
specific surface area, ZrO2(383) had a smaller W uptake than ZrO2(T). This
behavior depends on the polyoxometalate anion size and the microporous stru
cture of hydrous zirconium oxide. The depth of penetration of the Cr(VI), M
o(VI), and W(VI) anionic species in the grains of the ZrO2(383) support was
estimated by quantitative XPS measurements and by electron microscopy dete
rminations. The nuclearity of the adsorbed species is also briefly discusse
d.