CERIA ON SILICA AND ALUMINA CATALYSTS - DISPERSION AND SURFACE ACID-BASE PROPERTIES AS PROBED BY X-RAY-DIFFRACTOMETRY, UV-VIS DIFFUSE-REFLECTANCE AND IN-SITU IR ABSORPTION STUDIES
Mi. Zaki et al., CERIA ON SILICA AND ALUMINA CATALYSTS - DISPERSION AND SURFACE ACID-BASE PROPERTIES AS PROBED BY X-RAY-DIFFRACTOMETRY, UV-VIS DIFFUSE-REFLECTANCE AND IN-SITU IR ABSORPTION STUDIES, Colloids and surfaces. A, Physicochemical and engineering aspects, 127(1-3), 1997, pp. 47-56
X-ray diffractometry and UV-Vis diffuse reflectance spectroscopy revea
led that fluorite-structured CeO2 crystallites (mean size 22.3 ma) are
dispersed on silica surfaces (CeSi) into microcrystallites (11.2-8.1
nm) and dispersed further on alumina surfaces (CeAl) into nanocrystall
ites (<8.5 nm) and CeOx monolayers. Consequently, IR spectroscopy of a
dsorbed pyridine found Lewis acid sites to be far more strengthened on
CeAl. Bronsted acid sites (proton-donors) were probed exclusively on
CeAl. On the other hand, IR spectroscopy of adsorbed deuterated chloro
form (CDC,) showed the originally moderate Lewis base sites (low-coord
inated OH- and O2-) to be weakened on CeSi, but markedly strengthened
on CeAl. Lewis base sites exposed on ceria surfaces assume a strong nu
cleophilic reactivity. (C) 1997 Elsevier Science B.V.