Porous properties of coprecipitated Al2O3-SiO2 xerogels prepared from aluminium nitrate nonahydrate and tetraethylorthosilicate
Abstract
Al
2
O
3
-SiO
2
xerogels with various chemical compositions have been prepared by coprecipitation and their porous properties investigated by nitrogen gas adsorption, transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and
29
Si and
27
Al magic angle spinning nuclear magnetic resonance (MAS NMR). The precipitates were formed by adding conc. aqueous ammonia to an ethanol solution of Al(NO
3
)
3
·9H
2
O and Si(OC
2
H
5
)
4
(TEOS). The syntheses were performed both with and without added H
2
O(H
2
O/TEOS≥18/1). The xerogels were dried and calcined at 300 °C for 4 h. The porous properties [specific surface area (S
A
), pore volume (V
p
) and pore size (r
P
)] varied with their chemical composition, especially the SiO
2
rich xerogels. The experimental S
A
values ranged from ca. 10 to 560 m
2
g
–1
, the V
P
values from 0.02 to 1.55 ml g
–1
and the r
P
values from 2 to 34 nm. The addition of H
2
O during the preparation markedly influenced the porous properties of the xerogels with SiO
2
rich composition. The structure and microtexture of the xerogels are discussed on the basis of the NMR, SAXS and TEM data.
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