Gas adsorption properties of mesoporous γ-alumina prepared by a selective leaching method
Abstract
Gas adsorption properties of mesoporous γ-Al
2
O
3
prepared by the selective leaching method were investigated using various adsorbate gases. The mesoporous γ-Al
2
O
3
was prepared by calcining kaolinite to form a microtexture of fine γ-Al
2
O
3
grains dispersed in a matrix of amorphous SiO
2
followed by selective leaching of amorphous SiO
2
from the microtexture. The mesopores were formed inside the pseudomorphic hexagonal platy particles of kaolinite. The specific surface area, total pore volume and pore size measured at 77 K using N
2
gas were ca. 240 m
2
g
–1
, 0.7 ml g
–1
and 6 nm, respectively. The gas adsorption isotherms of polar molecules such as water, methanol and butan-1-ol showed type IV isotherms (IUPAC classification) while those of non-polar molecules such as cyclohexane showed type V isotherms. The γ-Al
2
O
3
was therefore recognized as having hydrophilic surface characteristics. The onset of adsorption of these gases in the low relative pressure (P/P
0
) region was methanol>water>butan-1-ol>cyclohexane, this order corresponding to the affinity between the adsorbate gas and surface of the γ-Al
2
O
3
and also reflecting the steric effect of adsorbate gas. The fractal dimension obtained from the BET monolayer adsorption capacity plot was 2.1, indicating a smooth surface. The gas adsorption properties of the γ-Al
2
O
3
are discussed and compared with commercial γ-Al
2
O
3
and Al
2
O
3
-SiO
2
gel.
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