Inorganic Chemistry
Article
temperatures higher than 700 °C, when the thermodynamics
of the system indicates that it is favorable at much lower
temperatures. A possible explanation is that, during the
carbonation of Li8SiO8, an external shell of Li2CO3 is formed
over the newly formed Li4SiO4 particles, limiting the access of
CO2 to the internal Li4SiO4. Once the system reaches the
melting point of Li2CO3, the CO2 has free access to the core of
these particles and the Li4SiO4 carbonation finally occurs.
These results are in agreement with previous studies done in
the Li4SiO4 system.36
support. G.A. thanks CONICET, CNEA, ANPCyT (PICT no.
1052), and Instituto Balseiro (University of Cuyo).
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The solid-state synthesis of Li8SiO6, using Li2O and SiO2 as
reactants, was studied by in situ synchrotron powder X-ray
diffraction. Between 300 and 490 °C, Li2O and SiO2 react to
form Li4SiO4, while, at temperatures above 490 °C, Li4SiO4
swiftly reacts with the remaining Li2O to produce Li8SiO6. The
presence of LiOH, produced by exposure of Li2O to room
humidity, was identified together with the starting materials.
The quantity of this impurity decreased during the heating
process, due to its reaction to form Li2O. The in situ synthesis
allowed determining that, above 500 °C, the system reaches
the equilibrium very fast, making waiting for several hours to
complete the reaction unnecessary.
The second part of the present work was focused on the
study of the Li8SiO6 carbonation reaction in the temperature
range from room temperature to 780 °C. Time-resolved in situ
XRSPD allowed tracking phase transitions in real time at
temperatures that are of interest for the application of Li8SiO6
as high temperature CO2 sorbent and to propose a mechanism
of reaction. Studying the phase composition of the system, it
becomes clear that there is a first superficial absorption by
Li8SiO6 and then the reaction stops, probably due to diffusion
kinetic limitations. After increasing the temperature, the system
resumes this main reaction, consuming the remaining Li8SiO6
in the bulk absorption process. The in situ absorption
characterization allowed clearly determining the nature of the
double CO2 bulk chemical reaction process, which had been
previously observed but not explained, by showing the
increment on the amount of Li2SiO3 and the relative drop in
the amount of Li4SiO4 present in the system. It is important to
highlight that results obtained from the Rietveld refinements of
the in situ Li8SiO6 carbonation allowed reconstructing the
dynamic thermogram, and the results are in good agreement
with previously reported thermogravimetric measurements for
Li8SiO6. This allowed distinguishing reactions occurring at the
surface of the material from those taking place in the bulk.
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AUTHOR INFORMATION
Corresponding Author
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(15) Pan, Y.; Zhang, Y.; Zhou, T.; Louis, B.; O’Hare, D.; Wang, Q.
Fabrication of Lithium Silicates As Highly Efficient High-Temper-
ature CO2 Sorbents from SBA-15 Precursor. Inorg. Chem. 2017, 56,
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ORCID
(16) Duran-Munoz, F.; Romero-Ibarra, I. C.; Pfeiffer, H. Analysis of
̃
Notes
The authors declare no competing financial interest.
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(Li8SiO6): a new option for high-temperature CO2 capture. J. Mater.
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Dou, S. X.; Cho, J.; Kim, Y.-J. Scalable Integration of Li5FeO4 towards
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ACKNOWLEDGMENTS
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The authors thank the European Synchrotron Radiation
Facility for providing in-house beamtime at beamline ID31,
and Thomas Buslaps, Florian Russello, and Tiago Coutinho
Macara for their help in the experimental setup. K.K. thanks
the Academy of Finland (project 1295696) for financial
(18) Pacciani, R.; Torres, J.; Solsona, P.; Coe, C.; Quinn, R.; Hufton,
J.; Golden, T.; Vega, L. F. Influence of the Concentration of CO2 and
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