Three-step calcination synthesis of high-purity Li8ZrO 6 with CO2 absorption properties

Article abstract of DOI:10.1021/ic102035y

Li₈ZrO₆ contains a high lithium content and may bear a great ability of CO₂ absorption, yet the reports about the properties of CO₂ absorption on Li₈ZrO₆ are few to date for its difficulty in production. In this paper, high-purity Li ₈ZrO₆ is synthesized via a three-step calcination method combined with an effective lithium source and a suitable initial Li/Zr molar ratio. The produced Li₈ZrO₆ possesses a great CO ₂ absorption capacity of about 53.98 wt % at 998 K, which could be well-maintained in a wide range of CO₂ partial pressures of 0.1-1.0 bar although it decreased gradually during the multicycle process of CO ₂ absorption-desorption in a 10% CO₂ feed stream because of the high working temperature. These properties imply that Li ₈ZrO₆ may be a new option for high-temperature CO ₂ capture applied in industrial processes such as a steam methane reformer.

Full text of DOI:10.1021/ic102035y

ARTICLE
pubs.acs.org/IC
Three-Step Calcination Synthesis of High-Purity Li8ZrO6 with CO2
Absorption Properties
Xian-Sheng Yin, Qin-Hui Zhang,* and Jian-Guo Yu
State Key Lab of Chemical Engineering, College of Chemical Engineering, East China University of Science and Technology,
Shanghai 200237, People's Republic of China
S Supporting Information
b
ABSTRACT: Li8ZrO6 contains a high lithium content and may bear a great
ability of CO2 absorption, yet the reports about the properties of CO2
absorption on Li8ZrO6 are few to date for its difficulty in production. In this
paper, high-purity Li8ZrO6 is synthesized via a three-step calcination method
combined with an effective lithium source and a suitable initial Li/Zr molar
ratio. The produced Li8ZrO6 possesses a great CO2 absorption capacity of
about 53.98 wt % at 998 K, which could be well-maintained in a wide range of
CO2 partial pressures of 0.1-1.0 bar although it decreased gradually during
the multicycle process of CO2 absorption-desorption in a 10% CO2 feed
stream because of the high working temperature. These properties imply that
Li8ZrO6 may be a new option for high-temperature CO2 capture applied in
industrial processes such as a steam methane reformer.
’ INTRODUCTION
Thereby, it is highly desired to find a new absorbent with an
effective capacity of CO2 absorption in a low CO2 concentra-
tion atmosphere.
CO2 separation is important in the industrial processes such
as hydrocarbon reforming and purification, and CO2 capture
from the flue gas of coal-burning power plants is also one of
the possible solutions to eliminating the amount of CO2
emitted to the atmosphere.1-3 The CO2 produced in the
above processes is generally hot and coexisted with other
typical gases of H2, CO, N2, and H2O.4,5 In view of the energy
efficiency, it is more advisible to capture CO2 at high tem-
perature directly without cooling the gas stream to ambient
temperature prior to CO2 removal,6,7 yet the key problem is
the suitable CO2 absorbent with high stability and capacity at
high temperature. Various materials have been proposed and
developed as CO2 absorbents,8-14 in which lithium-based
ceramics present good properties as CO2 absorbents for high
capacity and selectivity at 773-1013 K.14 Li2ZrO3 was first
reported as a CO2 absorbent by Nakagawa and Ohashi15 in
1998 and considered to be a promising candidate of CO2
capture; after Li2ZrO3, several other lithium-based ceramics
Li8ZrO6 is well-known as a tritium breeder material with
advantages in safety, a lack of electromagnetic effects, and tritium
release.21-23 It was also reported that Li8ZrO6 shows a high ionic
conductivity and could be used as a conduction material.24
However, reports about the properties of CO2 absorption on
Li8ZrO6 are few to date despite the likely great CO2 absorption
capacity for its high lithium content.14 One of the reasons is the
difficulty in the synthesis of pure Li8ZrO6. Wyers and
Cordfunke22 synthesized Li8ZrO6 under vacuum with ZrO2
and Li2O obtained by thermal decomposition of LiOH; Zou
and Petric23 prepared Li8ZrO6 using ZrO2 and Li2O2 through
complicated heat-treating procedures. The reported synthesis
methods of pure Li8ZrO6 were not convenient and were difficult
to repeat under common experimental conditions. In this study,
pure Li8ZrO6 is synthesized via a simple three-step calcination
process, and the properties of CO2 absorption including the
effect of temperature, influence of the CO2 concentration, and
multicycle stability are investigated systematically.
20
such as Li4SiO4,16,17 Li6Zr2O7,18,19 and Li5AlO4 were also
reported as high-temperature CO2 absorbents. However, the
CO2 concentration in the industrial processes is normally low
(10-13%), and the CO2 absorption capacity for most of the
reported lithium-based ceramics is strongly limited by the
Received: October 7, 2010
Published: February 28, 2011
partial pressure of CO2 (PCO ) in the feed stream.4,5,16,19
2
r
2011 American Chemical Society
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’ EXPERIMENTAL METHODS
Experimental Procedures. Zirconium nitrate [Zr(NO3)4
3
5H2O] and lithium nitrate (LiNO3) were used as precursors
(Shanghai Chemical Co., Shanghai, China). Appropriate amounts of
each reagent were dissolved in deionized water and mixed with vigorous
stirring; after volatilization of the solvent at 363 K, the achieved powder
was grounded and reacted via a three-step calcination process in the
muffle. At the first step (calcination at 873 K for 2 h), Zr(NO3)4 was
decomposed as amorphous ZrO2 and dispersed in the molten LiNO3;
then, to avoid spilling over the crucible, the calcination temperature was
enhanced to 1073 K for another 2 h to convert the molten LiNO3 as
solid-state Li2O and reacted with ZrO2 to produce Li6Zr2O7 particles,
which was further reacted with excessive Li2O to produce a Li8ZrO6
layer on the particle surface. Finally, the calcination temperature was
enhanced to 1173 K for 72 h to improve diffusion of Li2O through the
external Li8ZrO6 layer and convert the internal Li6Zr2O7 as Li8ZrO6
Figure 1. XRD pattern of samples synthesized by calcination at 1173 K
using LiNO3 and Zr(NO3)4. Patterns a-d correspond to the sample
prepared with Li/Zr molar ratios at 8.0, 10.0, 12.0, and 14.0, respectively.
Pattern e corresponds to the standard pattern of rhombohedral-phase
Li8ZrO6. m(hkl): monoclinic-phase Li6Zr2O7. r(hkl): rhombohedral-
phase Li8ZrO6.
completely. Additionally, lithium hydroxide (LiOH H2O; Shanghai
3
Chemical Co., Shanghai, China) was chosen as a lithium resource to
compare the influence of different lithium sources for the synthesis of
pure Li8ZrO6.
Characterization of the Samples. The crystalline structures
were characterized by X-ray diffraction (XRD; Rigaku, D/max-RB using
Cu KR Ni-filtered radiation with λ = 1.5406 Å), scanning in the 2θ range
of 10-80° with a 10° min-1 step size. The relative percentages of
different crystal phases presented in the products were estimated
semiquantitatively from the total areas under the most intense diffrac-
tion peak of each phase identified.25,26 The morphology of the products
was analyzed by a scanning electron microscope (JSM-6360 LV), and
the samples were pretreated by covering with gold to overcome their
lack of electron conductivity. The Brunauer-Emmett-Teller (BET)
specific surface area was determined by a N2 adsorption-desorption
method at a liquid-nitrogen temperature (77 K) using a Micromeritics
ASAP-2010C instrument, and the samples were pretreated at 523 K for
3 h in a vacuum.
The CO2 uptake properties were tested under defined conditions
using a thermogravimetric analyzer (SDTQ600), and the testing pro-
cesses were similar to those in our previous report:19 For each test, about
15 mg samples were installed in the sample pan and heated from room
temperature to the working temperature with 20 K min-1 in a N2
atmosphere. Then the N2 flow was switched to the testing gas, and the
CO2 absorption process was started. The regenerability test was con-
ducted by heating the CO2 absorbed sample in a N2 flow at appropriate
temperatures. The multicycle test was conducted under the conditions
of uptake in a 10% CO2 atmosphere and desorption in a N2 atmosphere
at suitable temperatures for enough time, respectively.
Figure 2. Percentages for Li6Zr2O7 and Li8ZrO6 in the products
synthesized as a function of the initial Li/Zr molar ratio. 0: mono-
clinic-phase Li6Zr2O7. 9: rhombohedral-phase Li8ZrO6.
further increasing the initial Li/Zr molar ratios to 10.0, 12.0, and
14, and the percentage of Li8ZrO6 in each of the achieved
products is 76.39%, 94.34%, and 100%, respectively. This result
indicates that sublimation of Li2O decomposed from LiNO3 is
very serious during the recrystallization process, and the produc-
tion of pure Li8ZrO6 needs about 75% surplus lithium source in
the initial Li/Zr molar ratios. On the basis of the above analysis,
the synthesis mechanism of Li8ZrO6 could be speculated as eqs 1
and 2.
’ RESULTS AND DISCUSSION
Synthesis and Characterization of Pure Li8ZrO6. Figure 1
shows the XRD analysis of the achieved products prepared using
LiNO3 and Zr(NO3)4. Patterns a-d correspond to the samples
of Li/Zr molar ratios at 8.0, 10.0, 12.0, and 14.0, respectively;
pattern e is the standard pattern of rhombohedral-phase Li8ZrO6
(JCPDS 26-0867, a = 5.48 Å, and c = 15.45 Å). As can be seen, the
diffraction peaks of pattern a are comprised of monoclinic-phase
Li6Zr2O7 (JCPDS 34-0312, a = 10.45 Å, b = 5.99 Å, and c = 10.21
Å) and rhombohedral-phase Li8ZrO6, and the peaks of Li6Zr2O7
are weakened in patterns b and c when the Li/Zr molar ratio is
increased to 14.0; the corresponding pattern d is comprised of
only rhombohedral-phase Li8ZrO6. Figure 2 presents the rela-
tionship between the initial Li/Zr molar ratios and the content of
Li8ZrO6 in the products. Because the initial Li/Zr molar ratio is
8.0, the percentage of Li8ZrO6 in product a is only about 43.79%,
3Li2O þ 2ZrO2 f Li6Zr2O7
ð1Þ
ð2Þ
Li6Zr2O7 þ 5Li2O f 2Li8ZrO6
The choice of LiNO3 as the lithium source is another crucial
factor in the synthesis of Li8ZrO6. When lithium hydroxide
(LiOH H2O) is used instead of LiNO3, the Li6Zr2O7 impurity
3
is always presented in the products, even increasing the initial Li/
Zr molar ratio up to 20.0 (see Figures S1 and S2 in the
Supporting Information). Analysis of the scanning electron
microscopy (SEM) reveals that the products synthesized using
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Figure 3. SEM images of samples synthesized using different lithium
sources with an initial Li/Zr molar ratio at 14.0. Images a and b
correspond to the product of pure Li8ZrO6 synthesized using LiNO3
and Zr(NO3)4. Images c and d correspond to the product synthesized
using LiOH and Zr(NO3)4.
Figure 4. Thermogravimetric analysis curve of Li8ZrO6 analyzed in a
flux of CO2 with PCO at 0.1 bar.
2
LiNO3 and LiOH as lithium sources, respectively, exhibit very
different morphologies. As can be seen in Figure 3, the product
corresponding to LiNO3 is build up by shapely particles with an
average size of about 5.0 μm, indicating that an equable nuclea-
tion and growth process has happened, while the product
corresponding to LiOH is composed of larger bulks with
irregular shape, which may be due to the reaction (3) taking
place in the process of solution mixture, and the produced
Zr(OH)4 may be further decomposed and sintered to ZrO2
particles with very serious agglomeration during the heat treat-
ment procedures; then Li6Zr2O7 may be formed first with large
particle sizes, resulting in limitation of the thermal diffusion of
ions such as Liþ and O2-; subsequently, the internal Li6Zr2O7 of
the particle could not be further converted to Li8ZrO6 effectively.
Figure 5. Kinetics of CO2 absorption on Li8ZrO6 at different tempera-
tures in a 10% CO2 feed stream.
4LiOH þ ZrðNO3Þ4 f ZrðOHÞ4 V þ 4LiNO3
ð3Þ
Further, the CO2 absorption kinetics on Li8ZrO6 at various
temperatures with PCO at 0.1 bar are presented in Figure 5. At
2
Compared with the reported synthesis methods of Li8ZrO6, in
which Li2O (or Li2O2) and ZrO2 were used as precursors and
rigorous reaction conditions were required,22-24 the proposed
preparation method here presents several advantages: First,
LiNO3 is safer and more obtainable than Li2O (or Li2O2);
second, the designed three-step calcination process is effective
in the formation of Li8ZrO6; third, the synthesis process is
conducted under common conditions and can be repeated easily.
These advantages represent significant improvements in the
scope of Li8ZrO6 synthesis.
Kinetic Analysis of CO2 Absorption and Desorption. Con-
sidering the varied concentrations of CO2 produced in the
industry procedures, the focus of this study is on the properties
of CO2 absorption on Li8ZrO6 in a series of mixed gases of CO2
temperatures of 773-973 K, the CO2 absorption rates are slow
but increased gradually with enhancement of the operating
temperature, suggesting that a solid-state carbonate shell might
be formed on the surface of the particles during the CO2
absorption process (the melting point of Li2CO3 was at about
983 K);19 then at operating temperatures up to 998 K, a fast
weight gain is taking place within the initial 10 min with a
saturation capacity of 53.98 wt % weight gain; upon further
enhancement of the temperature to 1023 and 1073 K, the CO2
absorption rates are increased but not significantly, and the
achieved capacities of CO2 absorption are reduced fractionally
compared with that at 998 K. The behaviors of CO2 absorption
on Li8ZrO6 at different temperatures are consistent with the
results observed in Figure 4. The fast absorption behavior at 998
K may result from the facile diffusion of CO2 in the molten
carbonate shell and the improved thermal diffusion of ions (e.g.,
Liþ and O2-) in Li8ZrO6, and the fractional reduction of the
CO2 absorption capacities at 1023 and 1073 K may be attributed
to the release of partially absorbed CO2 at these temperatures.
The XRD patterns a-d shown in Figure 6 correspond to the
CO2-absorbed samples at 873, 923, 973, and 998 K for 30 min,
respectively. As can be seen, some Li2CO3 (JCPDS 22-1141, a =
8.359 Å, b = 4.977 Å, and c = 6.194 Å) and Li6Zr2O7 specific
and N2 with PCO varied from 1.0 to 0.1 bar. Figure 4 presents the
2
thermogravimetric behavior of sample Li8ZrO6 under an atmo-
sphere of PCO at 0.1 bar, which is close to the CO2 concentration
2
in the flue gas from a coal-burning power plant or the steam
methane reformer (SMR) process. As can be seen, Li8ZrO6 has a
very fast CO2 absorption rate at temperatures up to 1000 K and
starts to release CO2 at temperatures higher than 1100 K,
indicating that Li8ZrO6 is an effective high-temperature CO2
captor with about 50 wt % capacity.
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Figure 8. Comparison of CO2 absorption capacities in pure CO2 and
10% CO2 atmospheres for different lithium-based ceramics.
Figure 6. XRD analysis of the CO2-absorbed Li8ZrO6 sample at 873,
923, 973, and 998 K corresponding to patterns a-d, respectively: 1,
Li2CO3; 9, Li2ZrO3 (JCPDS 20-0647); 0, Li2ZrO3 (JCPDS 33-0843);
b, Li6Zr2O7; Δ, unknown phase.
absorption capacity for Li2ZrO3 was sharply reduced by about
80%,4 and the losses of capacities for the higher lithium content
materials of Li6Zr2O7 and Li4SiO4 are lower but are still about
13.3% and 30.5%, respectively,16,19 while Li8ZrO6 can preserve
100% capacity of CO2 absorption, which is the highest capacity of
CO2 capture from the low CO2 concentration atmosphere (10%
volume content) for the lithium-based ceramics reported to
date.14 In fact, the capacities of CO2 absorption for the lithium-
based ceramics are closely related with the lithium content in the
absorbents, and the absorbents with richer lithium content could
offer more absorption sites in the absorption process.14,19 There-
fore, if the lithium content in the lithium-based ceramic is low,
the rate of CO2 absorption may be greatly slowed with a decrease
of PCO because of the reduction of the effective collision
2
reaction, subsequently causing a loss of the achieved capacity
of CO2 absorption in the definite time; on the contrary, if the
lithium content in the lithium-based ceramics is high enough, the
amount of the effective collision reaction may be large even in the
low CO2 concentration atmosphere, and the capacity of CO2
absorption may be maintained. These may be the main reasons
for the different CO2 absorption performances of the four kinds
of lithium-based absorbents in the atmosphere of CO2 concen-
trations in the range of 0.1-1.0 bar.
Generally, the product of Li8ZrO6 synthesized in this study
represents significant improvements in the scope of high-tem-
perature CO2 absorption so far14 and may be a new option for
high-temperature CO2 capture in industrial processes such as
SMR (normally operated at 1073-1300 K).3-5
The regenerability of Li8ZrO6 after CO2 absorption is also
investigated by desorbing CO2 at different temperatures in a N2
flow of 250 mL min-1. Figure 9 shows the CO2 desorption
curves of the CO2-absorbed Li8ZrO6 sample (absorption at 998
K for 30 min in a 10% CO2 atmosphere) regenerated at 1123,
1148, and 1173 K, respectively. As was expected previously, the
absorbed CO2 in Li8ZrO6 could be released under high tem-
peratures; moreover, the regeneration rate is strongly dependent
on the desorption temperature. At 1123 K, the desorption
process is not complete even after 110 min; with an increase of
the working temperature, the desorption rate is obviously sped
up, and the absorbed CO2 can be entirely released within about
80 and 50 min at 1148 and 1173 K, respectively.
Figure 7. Curves of CO2 absorption on Li8ZrO6 at 998 K as a function
of the CO2 concentration.
diffraction peaks appear in patterns a and b, and the diffraction
peaks of Li6Zr2O7 gradually disappear with enhancement of the
absorption temperature. The CO2-absorbed sample at 998 K is
composed of Li2ZrO3 (JCPDS 33-0843, a = 5.427 Å, b = 9.031 Å,
and c = 5.423 Å; JCPDS 20-0647, a = 9.0 Å, b = 9.0 Å, and c = 3.43
Å) and Li2CO3. Accordingly, the reaction mechanism during
CO2 absorption on Li8ZrO6 could be presented as eqs 4 and 5
with the theoretical CO2 absorption capacity of 54.4 wt %, which
is very close to the observed experimental results of 53.98 wt %
(about 99.23% theoretical capacity) analyzed above.
Li8ZrO6 þ CO2 f Li6Zr2O7 þ Li2CO3
Li6Zr2O7 þ CO2 f 2Li2ZrO3 þ Li2CO3
ð4Þ
ð5Þ
Figure 7 shows the influence of PCO on the absorption rate
2
and the capacity of CO2 absorption on Li8ZrO6 at 998 K. As PCO
2
was increased from 0.1 to 1.0 bar, the absorption rate increased
from about 5.0 to 11.3 wt % min-1, with the absorption capacities
remaining almost invariable. This behavior is very different from
that of the previously reported lithium-based ceramics such as
Li2ZrO3, Li6Zr2O7, and Li4SiO4. Figure 8 presents the variances
Multicycle Performance of CO2 Absorption-Desorption
on Li8ZrO6. Further, Figure 10 shows the multicycle perfor-
mance of CO2 absorption-desorption on Li8ZrO6 under the
conditions of absorption at 1023 K in a 10% CO2 feed gas for
of the absorption capacities as PCO was decreased from 1.0 to 0.1
2
bar for the four kinds of lithium-based ceramics. The CO2
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Figure 9. Kinetics of CO2 desorption from the absorbed Li8ZrO6
at different temperatures in a N2 atmosphere with a flow rate of
250 mL min-1
.
Figure 10. Multicycle performance of CO2 absorption-desorption on
Li8ZrO6 with the conditions of absorption at 1023 K in a 10% CO2
feed stream and desorption at 1133 K in a N2 flow with a flow rate of
250 mL min-1 via thermogravimetric analysis.
Figure 11. SEM images of the samples derived from Li8ZrO6 after CO2
absorption and desorption. Image a corresponds to the CO2 absorbed
sample. Images b and c correspond to the samples that have undergone 1
and 11 cycles of CO2 absorption-desorption, respectively.
30 min and desorption at 1173 K in a N2 flow for 65 min. With an
increase of the cycle times, the absorption rate is decreased
gradually and the achieved absorption capacity for the corre-
sponding cycle is reduced subsequently; after 10 cycles, only
about 45.01% capacity is preserved.
available to explain the reduced capacity for Li8ZrO6. To validate
this speculation, the samples that have undergone different
absorption-desorption cycles are analyzed by SEM and BET,
respectively. Figure 11 presents the SEM images of Li8ZrO6,
including the CO2-absorbed sample (corresponding to image a)
and the regenerated samples (corresponding to images b and c).
Compared with the images of the fresh sample in Figure 3a,b, the
absorbed sample is comprised of larger particles with a loose layer
covering the surface, which may be the carbonate layer formed as
described in the other reports;19,27 interestingly, the sample that
has undergone one cycle of absorption-desorption is made up
of large numbers of small particles with sizes of 1.0-3.0 μm
(corresponding to image b), while the sample after 11 absorption-
desorption cycles is seriously sintered (corresponding to image
c). The results of BET analysis indicate that the surface areas of
fresh Li8ZrO6 and the sample after one absorption-desorption
cycle are decreased from 3.917 to 2.950 m2 g-1 (24.7% re-
duction). These results confirm that reconstruction and sintering
of the absorbent is serious under high temperature, subsequently
The reduced capacity during the multicycle process may be
caused by the following two points. First, as can be seen in
Figure 10, the fractional weight of the absorbent is lost during the
multicycle process (about 3.08% weight is lost after 11 cycles)
because of sublimation of Li2O during the desorption processes
under high temperature, which was also observed for Li6Zr2O7
and Li4SiO4, and may result in the reduction of the CO2
absorption capacity in the multicycle process.14,19 However,
the reduction of the capacity caused by the loss of Li2O after
11 cycles is only about 6.24% by theoretical calculation, while the
entire reduced capacity of the 11th cycle is about 54.99%
compared with that of the 1st cycle. So, the loss of Li2O may
be one of the reasons for the reduced capacities of CO2
absorption on Li8ZrO6 during the cycles but not the primary
reason. Second, it is reported that the formed Li2CO3 molten
phase could cause reconstruction and sintering of the lithium-
based absorbent under high temperature and result in the gradual
reduction of capacities during the cycles,19 which may also be
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Figure 12. Schematic illustration for CO2 absorption (at 1023 K) and desorption (at 1173 K) on Li8ZrO6. Steps a-c correspond to the first cycle of
CO2 absorption-desorption, and steps d-f correspond to the second cycle of CO2 absorption-desorption.
causing the gradual reduction of capacities during the multicycle
process.
mainly because of reconstruction and sintering of the absorbent
under high temperature, which is the major limitation for
utilization of Li8ZrO6 in high-temperature CO2 capture from
the flue gas of a coal-burning power plant and a SMR process.
On the basis of the above analysis, the multicycle process of
CO2 absorption-desorption can be depicted as steps a-f in
Figure 12. At the initial step of CO2 absorption, CO2 may be
easily diffused into the porosities of the Li8ZrO6 sample and
quickly reacted with Li8ZrO6 to produce Li2ZrO3 and Li2CO3
(corresponding to step a); because of the expandability of the
carbonate formed in the porosities, the large particles may be
broken up as a mass of small particles surrounded with molten
Li2CO3 combined with the loss of porosity (corresponding to
step b); then the absorbed sample is desorbed in a N2 flow, the
Li2ZrO3 particles may react with the surrounded Li2CO3 to form
reconstructed and sintered Li8ZrO6 particles, and the achieved
particles are smaller compared with the initial large particles
(corresponding to step c); besides, the surface area of the
regenerated sample may also be reduced because of the loss of
porosity, and fractional Li2O may be sublimed as well. In the
second cycle process of CO2 absorption-desorption, the ab-
sorption rate may be slower than that at the initial step because of
less surface area (corresponding to step e); moreover, the surface
area of the absorbent may be further reduced, and the small
particles may be sintered to larger particles in the regeneration
process (corresponding to steps f and g); as a result, the rate of
CO2 absorption may be decreased, gradually combining with a
reduced capacity for the following cycle.
’ ASSOCIATED CONTENT
S
Supporting Information. XRD analysis of the samples
b
synthesized using LiOH and Zr(NO3)4 and percentages of
different crystal phases in the products as a function of the initial
Li/Zr molar ratios. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: qhzhang@ecust.edu.cn. Tel/Fax: 86-21-64252171.
’ ACKNOWLEDGMENT
The research received financial support from National Science
Foundation of China (20976047) and Special Nano Science and
Technology Project of STCSM (0852 nm02100).
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High-purity Li8ZrO6 is successfully synthesized using LiNO3
and Zr(NO3)4 by a three-step calcination method and character-
ized as a high-temperature CO2 absorbent at different tempera-
tures in varied CO2 concentration atmospheres. The results
indicate that the Li8ZrO6 produced possesses about 53.98 wt %
capacity of CO2 absorption above 998 K; moreover, almost 100%
capacity could be preserved in a wide range of CO2 concentra-
tions (PCO at 0.1-1.0 bar), which presents a great improvement
2
in the scope of high-temperature CO2 absorption on lithium-
based ceramics. However, the capacity of CO2 absorption on
Li8ZrO6 is reduced gradually during the multicycle process
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