CO2 Absorption Studies on Mixed Alkali Orthosilicates Containing

Article pubs.acs.org/JPCC

CO2 Absorption Studies on Mixed Alkali Orthosilicates Containing Rare-Earth Second-Phase Additives P. V. Subha,† Balagopal N. Nair,*,‡,§ P. Hareesh,† A. Peer Mohamed,† T. Yamaguchi,∥ K. G. K. Warrier,†,⊥ and U. S. Hareesh*,†,⊥ †

Materials Science and Technology Division (MSTD), National Institute for Interdisciplinary Science and Technology, Council of Scientific and Industrial Research (CSIR-NIIST), Pappanamcode, Thiruvananthapuram, Kerala 695019, India ‡ R&D Centre, Noritake Company LTD, 300 Higashiyama, Miyoshi, Aichi 470-0293, Japan § Nanochemistry Research Institute, Department of Chemistry, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia ∥ Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226-8503, Japan ⊥ Academy of Scientific and Innovative Research, Delhi−Mathura Road, New Delhi 110 025, India ABSTRACT: Lithium silicate containing eutectic orthosilicate mixtures developed by a solid-state route displayed excellent characteristics as carbon dioxide absorbents at elevated temperature, showing absorption capacity of 256 mg g−1. Incorporation of second-phase materials was investigated as a strategy to enhance the stability of the absorbent materials against agglomeration and sintering during powder processing and high-temperature cyclic absorption/desorption loading. Yttrium oxide, gadolinium oxide, and lanthanum phosphate were added as second phases to the absorbent. It was found that when the composites were rich in absorbents (10:1 and 20:1 absorbent/second phase), the absorption performance was hardly influenced by the type of the secondphase material present. Yttrium oxide or gadolinium oxide additions in large quantities were found to enhance the absorption capacity of the orthosilicate phase. The 2:1 sample containing yttrium oxide gave absorption capacity of 315 mg g−1 of orthosilicate absorbent present in the composite sample. On the basis of the structural and morphological studies, we believe that the nonreactive second-phase components formed a virtual shell against the segregation of absorbent phase, thereby helping to improve their absorption performance. Cyclic studies have supported the superior stability and performance of such composite absorbent materials.

1. INTRODUCTION Carbon dioxide emission to the atmosphere is one of the major environmental issues in recent times because it is the largest contributor among the global anthropogenic greenhouse gas emissions. Selective CO2 capture followed by its sequestration is an effective approach to minimize its emission to the atmosphere. The development of highly efficient, cost-effective carbon dioxide capturing materials is an essential requirement to mitigate its tremendous rise in the environment. Conventionally, carbon dioxide capturing or purification from power plant flue gases is carried out by liquid absorbents such as aqueous monoethanol amine (MEA). However, most of the sorbents currently employed generate heavy energy penalty due to poor performance. In view of this, efforts to develop newer materials with better absorption/adsorption properties to selectively capture carbon dioxide from its sources of generation are ongoing worldwide.1−10 Notable achievements in the development of adsorbents based on metal organic frame works (MOFs), zeolites, and so on for CO2 adsorption at ambient temperatures have been reported in literature.1 The extremely high surface area and engineered pore sizes in such materials are desirable attributes. Alternatively, numerous strategies are currently being devised © 2015 American Chemical Society

for the development of regenerable sorbents to absorb carbon dioxide at high temperatures.11−17 The development of thermally stable sorbents with enhanced absorption kinetics and improved cyclic stability depends on several factors, and the major issue to be addressed is the tendency of sorbent particles to agglomerate and sinter at the elevated temperatures of use. Metal-oxide-based ceramic sorbent materials have significant applications in carbon dioxide absorption.18−23 Among the various ceramic absorbents, alkali metal ceramics based on lithium are presumed to be promising by virtue of their high absorbing ability, fast kinetics, and economic viability.24−29 In particular, lithium orthosilicate has the capacity to absorb in a wide range of temperatures (400−700 °C) and have low regeneration temperature (∼750 °C) compared with other sorbents. The pioneering work of Kato et al. (2002) reported a comprehensive study on the carbon dioxide absorption with lithium silicate under varying sorption conditions and convincingly showed that the absorption properties of lithium Received: November 29, 2014 Revised: February 20, 2015 Published: February 20, 2015 5319

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The Journal of Physical Chemistry C silicate are considerably better than that of lithium zirconate.7 Numerous synthetic approaches were reported for the synthesis of lithium-silicate-based materials including solid-state mixing, sol−gel method, ball-milling techniques, and combustion methods. Pfeiffer et al. compared synthetic approaches such as solid state, precipitation, and sol−gel methods on the synthesis of lithium silicates and also investigated the effect of synthesis procedure on the morphology of the resulting particles.30 Several other aspects have been reportedly used to control the carbon dioxide capture performance of lithium orthosilicate, including structural modification, alkali promotion, transition-metal doping, substitution of lithium by sodium, and so on.18,31−39 Romero-Ibarra et al. microstucturally modified lithium orthosilicate through ball milling and enhanced its cyclic stability without further sintering effects.40 Seggiani et al. modified Li4SiO4 using alkali carbonates and eutectic carbonate promoters at the optimum sorption temperature of 580 °C. Thirty wt % of the potassium carbonate addition showed better sorption properties and cyclic stability.41 In our previous work, we tailored the morphology of lithium orthosilicate particles through sol−gel approach, and the synthesized powders displayed enhanced absorption kinetics due to their platelet morphology.24 In the present investigation, attempts have been made to develop an economically viable CO2 absorbent material having superior absorption performance through the synthesis of a eutectic composition containing lithium-orthosilicate- and alkali-metal-based tertiary (Na/K/Li) carbonates. The degradation of absorption capacity and kinetics due to agglomeration or sintering of the particles while processing and during repeated absorption/desorption cycles are the major issues that are to be addressed when employing such low-temperature melting eutectic mixtures. We have incorporated thermally and chemically stable second-phase materials in the absorbent powders to impart stability against such high-temperature agglomeration and sintering. Lanthanum phosphate, a material well-known for its stability in reactive environments, and thermally stable rare-earth oxides, gadolinium oxide (gadolinia) and yttrium oxide (yttria), were used as second-phase components.42−44 We anticipated that the rare-earth ceramic particles will act as a virtual shell against the segregation of absorbent phase, thereby impeding particle agglomeration and imparting absorbent powders with superior performance.

M4SiO4 was prepared from a eutectic mixture of potassium, lithium, and sodium carbonates (M2CO3) with weight fractions of 20:50:30 (molar ratio of 15:68:28) and fumed silica in the molar ratio 2.2:1. The powders were initially mixed with a pestle and mortar and then ball-milled for 24 h in isopropanol. The mixture was then dried and calcined at 850 °C. The powder thus obtained was mixed with LaPO4, Y2O3, or Gd2O3 in the weight ratios 20:1, 10:1, 4:1, or 2:1 and heat-treated at 800 °C for 1 h to prepare the respective composites. 2.3. Material Characterization. The phase characterization of the powdered samples was performed by X-ray diffraction. X-ray scattering set-ups (Xeuss SAXS/WAXS system by Xenocs, France in the 2θ range 4−36° and PANalytical X’pert Pro diffractometer, Eindhoven, The Netherlands in the 2θ range 10−90°) were used to characterize the samples using Cu Kα radiation (λ = 0.154 nm). The morphological and microstructural analyses of the materials were carried out using a scanning electron microscope (SEM) operated at 20 kV. CO2 absorption studies were done using a TGA apparatus (PerkinElmer STA 6000, Netherlands) in the temperature range of 100−750 °C. In the setup used, actual temperatures close to sample were typically 5−10 °C lower than the set temperatures that are mentioned throughout this paper. CO2/nitrogen flow rates through the sample chamber were ∼50 mL/min unless otherwise mentioned.

3. RESULTS AND DISCUSSION The mechanism of carbon dioxide absorption in lithium silicate is well known and is discussed in previous literature.3 In the case of eutectic mixtures containing orthosilicates, the reaction with carbon dioxide resulted in the formation of corresponding metasilicate (M2SiO4) and carbonate (M2CO3) phases. The reaction could be represented by the following generalized equation. M4SiO4 + CO2 → M 2SiO3 + M 2CO3

(1)

M 2SiO3 + CO2 → M 2CO3 + SiO2

(2)

where M stands for a single alkali metal or a mixture of alkali metals. Eutectic mixture containing orthosilicates and synthesized through solid-state method was characterized using XRD. The X-ray diffraction (XRD) patterns of the samples revealed that the mixture contained orthosilicate and carbonate phases of sodium, lithium, and potassium (Figure 1). The presence of lithium metasilicate in the mixture could be due to the

2. EXPERIMENTAL SECTION 2.1. Materials. Fumed silica (purity 99.8%, Aldrich Chemicals, USA), Li2CO3 (98%), Na2CO3 (99.9%), and K2CO3 (99.8%, all carbonates procured from Merck, India) were used as raw materials for the preparation of lithiumsilicate-based eutectic mixtures (M4SiO4). For composite preparation, LaPO4 was synthesized as per procedure reported elsewhere,45 Y2O3 (99.9%) and Gd2O3 (99.9%) were procured from Aldrich Chemicals, USA. Surface area values (BET) of the precursor powders were measured as 46.3, 0.7, and 2.5 m2 g−1, and particle sizes (SEM/TEM) were measured as ∼50−100, ∼200−300, and ∼800 nm for LaPO4, Y2O3, and Gd2O3, respectively. All chemicals were used for the experiment without any further purification. 2.2. Lithium Silicate Composite Synthesis Using Chemically and Thermally Stable Materials (Y2O3, Gd2O3, LaPO4). Lithium-silicate-based composites (M4SiO4 + second phase) were synthesized by the solid-state reaction between the two components of the composite material. First,

Figure 1. XRD patterns of eutectic mixture containing orthosilicates synthesized by solid-state reaction. Peaks were indexed using the following JCPDS files: (Li4SiO4, JCPDS 37-1472), (Li2SiO3, JCPDS 29-0828), (Na4SiO4, JCPDS 27-0783), (K4SiO4, JCPDS 79-1102), (Li2CO3, JCPDS 01-1001),(K2CO3, JCPDS 70-0292), and (Na2CO3, JCPDS 86-0288). 5320

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The Journal of Physical Chemistry C absorption of carbon dioxide at room temperature by lithium orthosilicate phase and is in line with previous reports.24 Morphological characterization of the powder was carried out using SEM and is shown in Figure 2. The powder appeared as macroporous aggregates of particle with more or less spherical morphology with an average size range of ∼1 μm.

Figure 3. (a) Dynamic thermogravimetric plots of M4SiO4 and Li4SiO4 (data from ref 24). (b) Thermogravimetric weight gain/loss curve of M4SiO4 measured (100% CO2) with respect to time. The first absorption step was carried out at 550 °C and the second was carried out at 700 °C, and desorption was carried out at 700 °C by switching gas to N2. Heating rate used was 10 °C min−1 for heating from 550 to 700 °C.

was first exposed to CO2 at 550 °C and then at 700 °C. The maximum absorption capacity measured for the sample was 256 mg g−1. The desorption was carried out at 700 °C itself by switching gas to N2, and full weight loss due to CO2 release has been confirmed. One of the major issues limiting the commercial application of alkali-carbonate-based CO2 absorbents is the agglomeration and sintering of the particles at high temperature of the application, leading to decaying absorption kinetics with time. To limit this, we have investigated the addition of secondary phases to the absorbent. Figure 4 shows a schematic representation of an ideal system where second phases may limit or inhibit the segregation of the molten carbonate phase by boundary pinning as well as limit sintering of the absorbent particles. We have added chemically and thermally stable rare-earth ceramics LaPO4,Y2O3, and Gd2O3 to the absorbent. Y2O3 was selected based on its excellent thermal stability and resistance to chemical attack by molten metals and salt mixtures at high temperatures.42 Gd2O3 was selected as second phase due to the reported stability of gadolinia-doped ceria in high-temperature alkali-carbonate-based membranes.43 LaPO4 is well known for its thermal stability and corrosion resistance against molten metals and other chemically corrosive environments.44 The composites were prepared at weight ratios of 20:1, 10:1, 4:1, and 2:1, where absorbent was the major component of all mixtures prepared. The composites thus obtained were

Figure 2. SEM images of eutectic orthosilicates synthesized through solid-state reaction at viewing magnifications of (a) 10k and (b) 5k.

Initially the M4SiO4 samples were heated to the maximum absorption temperature at a heating rate of 20 °C min−1 under 100% CO2 flow. The resulting dynamic thermograms are shown in Figure 3a in comparison with similar thermograms of Li4SiO4 (data from our previous publication).24 M4SiO4 samples had a delay in the onset of desorption under a 100% CO2 atmosphere compared with Li4SiO4 samples. Such delay in the onset on desorption is normally found when Li:Si ratio is high.32 Three distinct absorption steps were visible during sorption process: (1) Absorption started in the low-temperature region 650 °C). A detailed comparison of absorption performance of nine more different samples (3 second phases, 3 different

Figure 5. XRD patterns of composites in the weight ratio 2:1 synthesized by solid-state reaction (a) M4SiO4+ Y2O3, (b) M4SiO4+ Gd2O3, and (c) M4SiO4+ LaPO4. (Li4SiO4, JCPDS 37-1472), (Li2SiO3, JCPDS 29-0828), (Na4SiO4, JCPDS 27-0783), (Na2CO3, JCPDS 860288), (Y2O3, JCPDS 41-1105), Gd2O3,(12-0797), and LaPO4, (320493).

Figure 6. Dynamic thermogravimetric plots of composites (weight ratio 2:1) measured at 20 °C min−1 (100% CO2). 5322

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The Journal of Physical Chemistry C compositions in each case) measured at 550 °C is shown in Figures 7−9. As in the case of Figure 3b, the absorption

maximum absorption values were reached, the temperature was further increased to desorb the CO2. The measured absorption capacity of the samples at 550 °C was mostly in line with the orthosilicate content of the samples, where samples having larger amounts of the absorbent part showed greater absorption capacity. The maximum absorption capacity values as well as desorption rate (750 °C) values of the samples are listed in Table 1. The LaPO4 addition was found to be marginally superior in terms of retaining absorption capacity compared with the other two second phases when the composites were absorbent-rich (20:1). However, second-phase rich samples 2:1 and 4:1 (as in Figure 6 and Table 1) gave the opposite picture. Here samples with LaPO4 addition showed poor performance with regard to absorption capacity. It should be noted from Table 1 that in all of the cases the absorption capacity went up with the increase in the amount of absorbent phase in the sample and the values approached that of the sample without any second phase (100% absorbent), which was 256 mg g−1, as in Figure 3b, when the second phase content was low. In the case of yttria-based composites, the maximum absorption capacity values were found to be more or less similar among the samples with different compositions, although the effective weight of absorbent was only 66.7% in the 2:1 sample compared with the 95.24% in the 20:1 sample. It can therefore be inferred that the nonreactive yttria prevented the aggregation of ortho silicate particles very well, thereby making most of the absorbent surface available for reaction leading to absorption and desorption, when the second phase was present in significant quantities. This effect is better represented in Figure 10a,b, where the maximum absorption capacity values as well as values normalized to the weight of the absorbent in the sample (absorption capacity/weight fraction of absorbent in the sample) are shown. It is clear that yttria and gadolinia samples at high concentrations helped to improve the absorption performance of the material. Lanthanum phosphate hardly improved the performance of the absorbent part of the composite. On the basis of the results obtained from the carbon dioxide absorption−desorption performance, it could be concluded that ytrria- and gadolinia-based composites helped to prevent the aggregation of orthosilicate phase at elevated temperatures. The composite formation should have helped in the prevention of performance deteriorating aggregation of the particles, as is clear from the results of the absorption studies.. After composite formation, the powder morphology appeared to contain spherical particles, as in Figure 11. We expect these spherical particles, which were generated in the mixture due to the presence of second phases, to form a virtual shell against the segregation of molten carbonate during the processing of the powders and during their application. However, we have not convincingly observed any specific property of the secondphase material, other than the formation of the virtual shell, as a reason for the enhancement of absorption properties. As a result, it is difficult to explain all of the reported results in terms of the properties of the specific second-phase compound. Further detailed investigations may be necessary to fully understand the relationship between the type of second-phase component and the absorption properties of the composites made of them. Although we have observed second-phase components clearly in the XRD spectra, the partial dissolution of second phase ions in molten carbonate cannot also be ruled out in this stage. The impact of any such dissolution on the

Figure 7. Thermogravimetric absorption curves of LaPO4-based composites measured at 550 °C.

Figure 8. Thermogravimetric absorption curves of Gd2O3-based composites measured at 550 °C.

Figure 9. Thermogravimetric absorption curves of Y2O3-based composites measured at 550 °C.

temperature was then increased to 700 °C to measure the maximum absorption capacity of each sample. Once the 5323

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The Journal of Physical Chemistry C Table 1. Maximum Absorption Capacity and Desorption Rate of Samples Having Different Compositions LaPO4 absorption capacity sample (mg g−1) 2:1 4:1 10:1 20:1

167.9 180.9 217.2 240.1

Gd2O3

Y2O3

desorption rate at 750 °C (mg g−1 min−1)

absorption capacity (mg g−1)

desorption rate at 750 °C (mg g−1 min−1)

absorption capacity (mg g−1)

desorption rate at 750 °C (mg g−1 min−1)

12.1 16.9 19.7 21.0

195.2 211.6 227.4 227.6

11.9 12.8 18.6 19.2

210.0 216.0 220.0 218.0

9.0 13.3 17.0 20.0

Figure 11. SEM images of composite absorbent powders in the ratio (2:1) (a) M4SiO4+ Y2O3 and (b) M4SiO4+ Gd2O3.

Figure 10. Comparative study of absorption capacity. (a) Amount absorbed per unit mass of the absorbent. (b) Amount absorbed per unit mass of the orthosilicate part of the absorbent as absorption capacity is shown normalized to the weight of the ortho silicate part of the absorbent in the mixture.

distribution of second phases for further improvements in the properties of such composite powders and to elevate their level of absorption to that of commercial absorbents.

chemical structure of the materials and absorption properties as in Figure 10 needs further detailed study. Cyclic absorption−desorption measurements were, therefore, carried out on the yttria-based 2:1 composite samples, and the results are shown in comparison with that of M4SiO4 sample (Figure 12a,b). The measurement was carried out at a static temperature of 700 °C by switching between 100% CO2 and 100% N2. The yttria-based composite powder demonstrated excellent cyclic stability, as shown in Figure 12b. The shape of the desorption branch is not commonly found in Li4SiO4 powders24 and should be due to the presence of secondphase particles that pins molten carbonate mobility. It should be noted that the absorption performance of the composite sample was better than M4SiO4 (Figure 12a), even with such constraints. The results of the present study therefore point to the feasibility of using second phases along with orthosilicate absorbent powders to effectively limit the aggregation of the powder particles and thereby improve their absorption properties. On the basis of structural and morphological studies we believe that the nonreactive second-phase components formed a virtual shell against the segregation of absorbent phase, thereby improving its performance. It is, however, noted that further efforts are required to study the concentration and

4. CONCLUSIONS Eutectic mixtures containing lithium-silicate-based absorbents for carbon dioxide absorption at elevated temperature were developed via solid-state method. Carbon dioxide absorption− desorption performance of the samples showed a maximum absorption capacity value of 256 mg g−1. The effect of secondphase addition on the agglomeration and sintering of the samples at elevated temperatures was investigated as a strategy to enhance their stability for cycling loading.Y2O3, Gd2O3, and LaPO4 were added as second phases to the orthosilicate absorbent, and it was found that when the composites were rich in absorbents (10:1 and 20:1 absorbent/second phase) the absorption performance was hardly influenced by the type of second phase present. However, when the amount of second phase was higher (2:1) the absorption properties of the composite powder were influenced by the type of absorbent. Y2O3 and Gd2O3 addition was found to enhance the absorption properties of the orthosilicate phase in the composite sample. On the basis of structural and morphological studies we believe that the nonreactive second-phase components formed a virtual shell against the segregation of absorbent phase, thereby improving its performance. Cyclic studies have supported the 5324

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(3) Nair, B. N.; Burwood, R. P.; Goh, V. J.; Nakagawa, K.; Yamaguchi, T. Lithium Based Ceramic Materials and Membranes for High Temperature CO2 Separation. Prog. Mater. Sci. 2007, 54, 511− 541. (4) Zhao, C.; Zhou, Z.; Cheng, Z. Sol−Gel-Derived Synthetic CaOBased CO2 Sorbents Incorporated with Different Inert Materials. Ind. Eng. Chem. Res. 2014, 53, 14065−14074. (5) Mejà a-Trejo, V. L.; Fregoso-Israel, E.; Pfeiffer, H. Textural, Structural, and CO2 Chemisorption Effects Produced on the Lithium Orthosilicate by Its Doping with Sodium (Li4‑xNaxSiO4). Chem. Mater. 2008, 20, 7171−7176. (6) Venegas, M. J.; Fregoso-Israel, E.; Escamilla, R.; Pfeiffer, H. Kinetic and Reaction Mechanism of CO2 Sorption on Li4SiO4: Study of the Particle Size Effect. Ind. Eng. Chem. Res. 2007, 46, 2407−2412. (7) Du, J.; Corrales, L. R. Characterization of the Structural and Electronic Properties of Crystalline Lithium Silicates. J. Phys. Chem. B 2006, 110, 22346−22352. (8) Nakagawa, K.; Ohashi, T.; Novel, A. Method of CO 2 Capture from High Temperature Gases. J. Electrochem. Soc. 1998, 145, 1344− 1346. (9) Essaki, K.; Kato, M.; Uemoto, H. Influence of Temperature and CO2 Concentration on the CO2 Absorption Properties of Lithium Silicate Pellets. J. Mater. Sci. Lett. 2005, 40, 5017−5019. (10) Nair, B. N.; Yamaguchi, T.; Kawamura, H.; Nakao, S. I.; Nakagawa, K. Processing of Lithium Zirconate for Applications in Carbon Dioxide Separation: Structure and Properties of the Powders. J. Am. Ceram. Soc. 2004, 87, 68−74. (11) Yamaguchi, T.; Niitsuma, T.; Nair, B. N.; Nakagawa, K. Lithium Silicate Based Membranes for High Temperature CO2 Separation. J. Membr. Sci. 2007, 294, 16−21. (12) Rodriguez-Mosqueda, R.; Pfeiffer, H. High CO2 Capture in Sodium Metasilicate (Na2SiO3) at Low Temperatures (30−60 °C) through the CO2-H2O Chemisorption Process. J. Phys. Chem. C 2013, 117, 13452−13461. (13) Wang, S.; An, C.; Zhang, Q.-H. Syntheses and Structures of Lithium Zirconates for High-Temperature CO2 Absorption. J. Mater. Chem. A 2013, 1, 3540−3550. (14) Olivares-Marín, M.; Drage, T. C.; Maroto-Valer, M. M. Novel Lithium-Based Sorbents from Fly Ashes for CO2 Capture at High Temperatures. Int. J. Greenhouse Gas Control. 2010, 4, 623−629. (15) Zaman, M.; Lee, J. Carbon Capture from Stationary Power Generation Sources: A Review of the Current Status of the Technologies. Korean J. Chem. Eng. 2013, 30, 1497−1526. (16) Iddir, H.; Curtiss, L. A. Li Ion Diffusion Mechanisms in Bulk Monoclinic Li2CO3 Crystals from Density Functional Studies. J. Phys. Chem. C 2010, 114, 20903−20906. (17) Chen, H.; Zhang, G.; Wei, Z.; Cooke, K. M.; Luo, J. Layer-byLayer Assembly of Sol-Gel Oxide ″Glued″ Montmorillonite-Zirconia Multilayers. J. Mater. Chem. 2010, 20, 4925−4936. (18) Shan, S.; Jia, Q.; Jiang, L.; Li, Q.; Wang, Y.; Peng, J. Novel Li4SiO4-Based Sorbents from Diatomite for High Temperature CO2 Capture. Ceram. Int. 2013, 39, 5437−5441. (19) Yin, X.-S.; Zhang, Q.-H.; Yu, J.-G. Three-Step Calcination Synthesis of High-Purity Li8ZrO6 with CO2 Absorption Properties. Inorg. Chem. 2011, 50, 2844−2850. (20) Wang, K.; Guo, X.; Zhao, P.; Wang, F.; Zheng, C. High Temperature Capture of CO2 on Lithium-Based Sorbents from Rice Husk Ash. J. Hazard. Mater. 2011, 189, 301−307. (21) Duran-Munoz, F.; Romero-Ibarra, I. C.; Pfeiffer, H. Analysis of the CO2 Chemisorption Reaction Mechanism in Lithium Oxosilicate (Li8SiO6): A New Option for High-Temperature CO2 Capture. J. Mater. Chem. A 2013, 1, 3919−3925. (22) Nakagawa, K.; Ohashi, T.; Novel, A. Method of CO2 Capture from High Temperature Gases. J. Electrochem. Soc. 1998, 145, 1344− 1346. (23) Romero-Ibarra, I. C.; Duran-Munoz, F.; Pfeiffer, H. Influence of the K-, Na- and K-Na-Carbonate Additions During the CO2 Chemisorption on Lithium Oxosilicate (Li8SiO6). Greenhouse Gases Sci. Technol. 2014, 4, 145−154.

Figure 12. (a) Cyclic absorption−desorption performance of M4SiO4 at 700 °C, 9 cycles. (b) Cyclic absorption−desorption performance (10 cycles) at 700 °C of M4SiO4+ Y2O3 composite in the ratio (2:1).

superior stability and performance of such composite absorbent materials.

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AUTHOR INFORMATION

Corresponding Authors

*U.S.H.: E-mail: [email protected] *B.N.N.: E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the Council of Scientific and Industrial Research (CSIR), New Delhi, India and Noritake Co. Limited, Aichi, Japan for providing research facilities and financial support through the grants of SURE (CSC 0132) and CLP 218739, respectively.

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REFERENCES

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DOI: 10.1021/jp511908t J. Phys. Chem. C 2015, 119, 5319−5326