The layered double
hydroxides (LDHs) of Ca
2+
and trivalent
cations, Al
3+
and Fe
3+
, are single-source precursors
to generate supported CaO, which picks up CO
2
from the
gas phase in the temperature range 350–550 °C. The supports
are ternary oxides, mayenite, and Ca
2
Fe
2
O
5
. The uptake capacity of the Fe
3+
-containing LDH
at 1.9 mmol g
–1
is two times the capacity of the
Al
3+
-containing LDH. The product of CO
2
uptake
is calcite CaCO
3
. It is observed that the intercalated
chloride ions reduce the thermal penalty by inducing the early decomposition
of CaCO
3
. In the case of the chloride-intercalated LDHs
of Ca
2+
and Fe
3+
, the CaCO
3
formed
is completely decomposed at 900 °C. This is in contrast with
the CaCO
3
formed from bare CaO, which shows no sign of
decomposition at 900 °C under similar conditions. This work shows
that the hydrocalumite-like LDHs are candidate materials for CO
2
mineralization.
Rapid and controlled precipitation of the hydroxide phases from a mixed metal nitrate solution comprising Ca2+ and Al3+ ions leads to the formation of 1H and 3R polytypes of [Ca–Al] layered double hydroxide respectively.
Hydrocalumite-like layered double hydroxides are anionic clays comprising positively charged metal hydroxide layers of the composition [Ca 2 Al(OH) 6 (H 2 O) 2 ] + . The water molecules provide the seventh coordination for the Ca 2+ ion. Anions are intercalated in the interlayer space to balance the charge leading to a class of LDHs having the formula [Ca 2 Al(OH) 6 (H 2 O) 2 ]·A (A = Cl, Br, I). Upon dehydration the Ca 2+ ion gets coordinatively unsaturated, and crystal chemical considerations dictate that the layered structure should collapse. When A = ClO 4 -, the LDH dehydrates fully below 80°C, but the layered structure is retained [a]
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