A one-pot method for the synthesis of hierarchically
structured ceria-silica composite materials is reported along with the
results of their characterization by a variety of physical techniques.
Crystallization of ceria in an aqueous mixture of anionic, cationic, and
neutral surfactants, namely Pluronic P123 (EO
20
PO
70
EO
20
), CTAB
(hexadecyltrimethylammonium bromide), and SDS (sodium dodecyl
sulfate) leads to the formation of a suspension of capped ceria
nanoparticles. Subsequent addition of tetraethoxysilane followed by
aging at 40
−
80
°
C leads to the condensation of silica. After thermal
removal of the organic species, the formation of high surface area
composites directed by the interaction of the capped nanoparticles and the remaining surfactants is possible. The thermal stability
and redox activity of the composite materials have been studied by in situ powder X-ray di
ff
raction, TGA/DSC, transmission
electron microscopy, Ce L
III
-edge XANES, and temperature-programmed reduction under H
2
/N
2
. Encapsulation of the ceria
nanoparticles in the templated silica matrix leads to high thermal stability with the nanocrystalline nature of the ceria retained
upon heating to 900
°
C in air with no annealing evident by in situ thermodi
ff
ractometry. Temperature-programmed reduction
shows large hydrogen uptake at around 600
°
C, corresponding to complete reduction of all Ce(IV) to Ce(III) in the case of a
cerium-rich sample (Ce:Si = 5:12). This reduction leads to amorphization of the ceria followed by the collapse of the hierarchical
structure with formation of Ce
2
Si
2
O
7
crystallites embedded in amorphous silica. For a sample of lower cerium content, crystalline
Ce
6
(Si
4
O
13
)(SiO
4
)
2
is formed under reductive conditions
departmental parameterization:
35
affiliation:
Wydział Chemii : Zakład Chemii Nieorganicznej, Wydział Chemii : Zakład Technologii Chemicznej