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Published on the web April 20, 2011
Evidence of CO Chemisorption at High Temperature in Lithium Gallate (Li GaO )
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Tatiana Ávalos-Rendón and Heriberto Pfeiffer*
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México,
Circuito Exterior s/n Cd. Universitaria, Del. Coyoacán, CP 04510, México DF, Mexico
(
Received February 3, 2011; CL-110097; E-mail: pfeiffer@iim.unam.mx)
Li GaO was tested as a possible CO captor. Li GaO was
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synthesized by solid-state reaction, structurally characterized,
and then thermally treated under a CO2 flow, from 30 to 900 °C,
(
B) Li GaO after the
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CO chemisorption
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having the highest CO chemisorption at around 709 °C. The
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results clearly showed that Li5GaO4 is able to trap CO2
chemically in two different steps. The CO2 quantity trapped
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was equal to 8.9 mmol g , which is considerably high in
comparison to other ceramics.
(
A) Li GaO4
The increase of carbon dioxide (CO ) in the atmosphere is
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claimed to be one of the major contributors to the greenhouse
effect and will result in serious global warming issues, such as
melting icebergs in the polar regions, hotter summer and winters
never seen before, all of them due to the global increment of
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temperature.
In that sense, in the last years, different lithium ceramics
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15 20 25 30 35 40 45 50 55 60
410
2θ /degree
have been proposed as possible CO captors.
Among all
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these ceramics, Li4SiO4, Li4TiO4, Li6Zr2O7, and Li5AlO4, seem
to have the best theoretical and experimental CO2 capture
Figure 1. XRD patterns of the Li5GaO4 sample (A) and the Li5GaO4
sample after the CO2 chemisorption process (B). Peaks labeled as
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,8,1015
efficiencies.
In fact, in a recent paper Ávalos-Rendón
and
correspond to Li2CO3 (87-0728 JCPDS card) and LiGaO2
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et al. proposed Li5AlO4 as a new CO2 captor, and the results
presented in that paper showed the highest experimental CO2
absorption reported in the literature, up to now, for this kind of
(72-1640 JCPDS card) compounds, respectively.
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materials, 16.4 mmol g (maximum CO2 theoretical capacity,
later). As it can be seen, Li2CO3 was detected as a secondary
phase (<8%). In fact, the presence of Li2CO3 may indicate
certain reactivity between the Li GaO and CO or the reaction
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19.8 mmol g ).
On the other hand, lithium gallate (Li GaO ) has been
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scarcely studied, and it has been mainly tested as a lithium ion
of the Li2O added in excess, as lithium carbonate was not used
as reagent, and it must be produced due to the CO2 capture of
Li5GaO4 from the environment. In addition, the N2 adsorption
desorption isotherm was obtained, and then the surface area of
this sample was estimated using the BET model. The surface
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conductor.
Additionally, it has to be pointed out that
Li5GaO4 and Li5AlO4 are isostructural materials. It is important,
as Li AlO has been shown to be one of the best possible CO
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captor ceramics. Both ceramics have orthorhombic phases,
where the cell parameters varied from 9.173, 9.094, and 9.202 ¡
to 9.087, 8.947, and 9.210 ¡ for Li GaO and Li AlO ,
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area was equal to 1 m g . Although the surface area is
considerably small, it is comparable with the other surface areas
presented by different lithium ceramics used for CO2 capture,
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8,19
respectively.
Therefore, based on the high lithium content
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of Li5GaO4 and the fact that it is an isostructural material with
Li AlO , the aim of this work was to study and demonstrate if
where the surface areas usually do not exceed 3 m g
.
Once the Li GaO was characterized, the material was
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Li5GaO4 is able to capture CO2, through a similar mechanism to
that reported previously for other lithium ceramics.
thermally treated under a CO2 flow to analyze if this material
can function as CO2 captor (CO2 flow used was equal to
60 mL min ). If Li GaO were able to react with CO , one of
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Li GaO was synthesized by solid-state reaction using
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gallium oxide (Ga2O3, Aldrich) and lithium oxide (Li2O,
Aldrich) as reagents, where 30 wt % excess lithium oxide was
used to prevent lithium sublimation. If this excess lithium was
not added or added in smaller quantities, the Li GaO was not
correctly synthesized (see Supporting Information ). Powders
were mechanically mixed and pressed. Then, a pellet was
thermally treated at 500 °C for 24 h. Finally, the sample pellet
was air-coolded and pulverized.
the following reactions may occur:
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Li5GaO þ 5CO2 ! 5Li2CO þ Ga2O
ð1Þ
ð2Þ
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Li5GaO þ 4CO2 ! 4Li2CO þ 2LiGaO2
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where the reaction would be similar to those observed for other
lithium ceramics,
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in which lithium carbonate is produced
in addition to a residual compound, Ga O or LiGaO in these
cases. For this reaction, the maximum theoretical CO2 capacity
on Li5GaO4 corresponds to 14.8 (reaction 1) or 11.8 mmol g
(reaction 2). These are smaller CO absorption capacities, in
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Figure 1 shows the XRD patterns of the Li5GaO4 sample
synthesized by solid-state reaction and the same sample after the
CO2 chemisorption process (the second pattern is described
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comparison to the isostructural aluminium ceramic (Li5AlO4).
Chem. Lett. 2011, 40, 504505