o2 release of mn-based oxygen carrier for chemical ...(schreiber et al., 2013), pressure swing...

Aerosol and Air Quality Research, 16: 453–463, 2016 Copyright © Taiwan Association for Aerosol Research ISSN: 1680-8584 print / 2071-1409 online doi: 10.4209/aaqr.2014.07.0140

O2 Release of Mn-Based Oxygen Carrier for Chemical Looping Air Separation (CLAS): An Insight into Kinetic Studies Wenju Wang1*, Bin Zhang1, Guoping Wang1, Yunhua Li2†

1 School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, China 2 Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, National Engineering Laboratory for Green Chemical Productions of Alcohols-Ethers-Esters, Xiamen University, Xiamen 361005, China ABSTRACT

Chemical looping air separation (CLAS) is an air separation technology with a relatively small energy footprint. In this contribution, the kinetic study of Mn-based oxygen carriers has been carried out in a CLAS process. The O2 release behavior was investigated under Ar in a fixed bed. Results showed O2 release amounts increase gradually with an increasing temperature. Moreover, fitting various gas-solid reaction mechanisms with the experimental data was used to obtain the chemical reaction kinetics for MnO2 and Mn2O3 for O2 release. As for all involved gas–solid reaction mechanisms, the first-order chemical reaction model (C1) and Avrami–Erofe’ev random nucleation and subsequence growth model (A2) fitted well with O2 release experimental data for MnO2 and Mn2O3, respectively. Furthermore, activation energy, pre-exponential factor and reaction order were also determined for these models. Keywords: Mn-based oxygen carrier; Kinetic; Activation energy; Chemical looping air separation (CLAS); O2 release. INTRODUCTION

Oxygen (O2) is the most common element in the earth's crust, and the second largest industrial gas (after N2) (Castle, 2002; Kerry, 2007; Häring, 2008). Oxygen is mainly used in the metal-mechanic industries, oxidation of the natural gas, medical unit, and integrated gasification combined cycle (IGCC) (Andersson and Johnsson, 2006), oxy-fuel combustion (Yin et al., 2008), solid oxide fuel cell (SOFC) (Hutchings et al., 2008), and so on. Several technologies are commercially employed to produce O2, including cryogenic distillation (the most common method) (Castle, 2002; Kerry, 2007; Häring, 2008), membrane separation (Schreiber et al., 2013), pressure swing adsorption (PSA) (Hassan and Ruthven, 1986; Jiang et al., 2003). Cryogenic distillation, with high investment costs, is a well-developed and established technique for large-scale production of pure oxygen. Membrane separation methods, in spite of less energy intensive, are expensive because of expensive and * Corresponding author. Tel./Fax: +86-025-84312577 E-mail address: [email protected]

† Corresponding author. Tel./Fax: +86-0592-2185203 E-mail address: [email protected]

complicated their fabrication, installation, and integration (Pfaff and Kather, 2009). PSA processes are usually applied in smaller scale, when it is sufficient with lower purity, typically around 95 vol.% oxygen. Although conventional separation methods are mature technologies, they are limited because of high energy consumption and costs, facing global environmental change and energy shortage (Hashim et al., 2011; Moghtaderi et al., 2011). Chemical absorption process may be a rather competitive alternative if the facility corrosion could be reduced. Compared with these technologies, the chemical looping air separation (CLAS), proposed by Mogtaderi et al. (Moghtaderi, 2010; Moghtaderi et al., 2011; Shah et al., 2011; Moghtaderi, 2012; Shah et al., 2012), has the advantages of operation-simple, cost- efficient, and energy-saving. The average specific power of CLAS (about 0.08 kWh m–3) is only 26% of that of an advanced cryogenic air separation system (Moghtaderi, 2010). The CLAS involves two separate fluidized bed reactors, between which there is a loop seal to prevent gas leakage from one reactor to another, thus keeping N2 from entering the O2 release reactor. In the O2 uptake reactor, the reduced oxygen carrier (OC) is oxidized by air, and then the oxide OC is transported to the O2 release reactor. In the O2 release reactor, the oxygen uncoupling occurs. The successful run of CLAS is greatly determined by the regenerative nature of OC.

However, the selection of effective OC materials is probably a challenge. In comparison with the OC for normal

Wang et al., Aerosol and Air Quality Research, 16: 453–463, 2016 454

chemical looping combustion (CLC) where the fuel (gaseous or solid) reacts directly with the OC without any release of gas phase O2, there is a special requirement for the OC in the CLAS process. The OC materials include CuO, Mn2O3, Co3O4, Pb3O4, CrO2, SrO2, PdO2, and CeO2 (Azimi et al., 2011; Imagawa et al., 2011; Adánez-Rubio et al., 2012; Wang et al., 2013). Among these oxides, Pb3O4 is poisonous, PdO2 is expensive, and the O2 release rate of SrO2, CeO2, and CrO2 is low. However, only three metal oxides (CuO, Mn2O3 and Co3O4) can be used as active compounds for CLAS (Mattisson et al., 2009) because of a suitable equilibrium O2 partial pressure at 800–1200°C. The maximum oxygen transport capacity is 0.1, 0.03 and 0.066 (g O2)·(g OC)–1 for the pairs CuO/Cu2O, Co3O4/CoO and Mn2O3/Mn3O4, respectively. So far none of OC employed in the CLAS process can effectively satisfy the air separation requirements (Moghtaderi, 2010; Moghtaderi, 2012).

The main parameters of the CLAS reactors are determined based on the knowledge of O2 release kinetics of OC. Reactivity data for a great deal of materials have been found, however, they have often been acquired for a single operational condition (Lyngfelt et al., 2008). A lot of experimental studies have been performed in a thermogravimetric analyzer (TGA). The temperature programmed reduction (TPR) or temperature programmed oxidation (TPO) technique also has been used for kinetic determination at a very low temperature. Others facilities have been also used to diminish mass transfer limitations (Bohn et al., 2009; Chuang et al., 2009, 2010) or to account for the mass transfer processes (Iliuta et al., 2010). Chadda et al. (1989) found that CuO have a very high activation energy (313 kJ mol–1) for the O2 release. However, few studies are focus on the O2 release of Mn-based oxygen-carriers in CLAS. Further research on the O2 release of Mn-based oxygen carriers for CLAS will be required in the future.

In a word, Mn-based oxygen carriers can actually meet the CLAS requirements. However, there is a limited capacity to optimize their performance since information on OC properties/characteristics in CLAS is quite inappropriate. Therefore, further research on Mn-based oxygen carriers is required to use in CLAS. This work focuses on reaction kinetics of Mn-based oxygen carriers for CLAS. EXPERIMENTAL Oxygen Carrier Materials

Manganese dioxide (MnO2) was purchased from Sinopharm Chemical Reagent Co., Ltd. The sample was analytical reagent (AR) and used directly. 7 g of MnO2, and 100 g of stainless steel balls were put into the planet balling mill. After ball milling for 10 h, the crushed samples were sieved to obtain smaller particles with the particle size distribution is in the range of 140–160 mesh (average size is 100 µm). The sample prepared is referred to as MnO2. The MnO2 powders obtained were further heated at 600°C for 6 h. The calcined samples were crushed, and sieved to obtain smaller particles with the particle size distribution is in the range of 140–160 mesh (average size is 100 µm). The sample prepared is referred to as Mn2O3. The oxygen carriers (about 100 mg)

were analyzed using X-ray diffraction (XRD, Bruker D8 Advance). Fixed BED SYSTEM

The kinetics of O2 release of MnO2 and Mn2O3 were conducted in a laboratory scale fixed bed reactor. The schematic diagram of fixed bed reactor was shown in Fig. 1. A quartz tube (length = 300 mm, i.d. = 20 mm) is located inside an electric furnace. The temperature inside the reaction tube is monitored by K type thermocouple in real time. The O2 release is tested under highly pure Ar atmosphere. 300 mL min–1 Ar was flowed into the reactor through the porous plate. The mass of oxygen carrier is 500 mg. Before the test, Ar was introduced into the reaction tube to sweep the residual O2. Then the reactor was heated in Ar atmosphere. As the temperature was stable for 60 min, the quartz boat (filled with oxygen carrier particles) was pulled from left to center by platinum wire using Ar as protective gas. Then the gap was sealed with a sealant. The start and completion of the oxygen release were marked by the emergence and vanishing of oxygen in the gas products, respectively. Kinetic Mechanism of Oxygen Release

In order to explore the kinetic characteristics of OC, the conversion rate α of OC at different temperatures was calculated by Eq. (1). The conversion rates of MnO2 and Mn2O3 are represented by α.

0

t

ox red

x Qdt

m m

(1)

where t (s) is the end time of oxygen release, x (mol%) is molar concentration of O2 in the gas products, and Q (mol/s) is the molar flow rate of gas products.

Reaction kinetics focuses on pre-exponential factor A (s–1), kinetic constant k, activation energy E (kJ mol–1), the integrated form of mechanism function G(α) or the differential form f(α). The relationship between E, A and k can be expressed by Arrhenius formula [Eq. (2)]. f(α) and k can mutually convert through Eq. (3), and the relationship between f(α) and G(α) is described by Eq. (5). In Eq. (5), k is constant at constant temperature and G(α) is linearly related to t, which is used to determine the G(α) of the reaction process. The linear correlation between G(α) and t is described by coefficient r. When r is closer to 1, the linearity is better. And the corresponding G(α) is more possibly the mechanism function that we seek. We calculated the coefficient r by bringing fourteen G(α)s (Wang et al., 2013) (shown in Table 1) into Eq. (5), which resulted in many G(α)s that exhibit good linear correlation with t. Therefore, the intercept of the line formed by G(α) and t was further calculated to determine the mechanism function. The G(α) with intercept near to zero was chosen as the mechanism function of this reaction. The kinetic constant k at various temperatures was calculated by Eq. (3). By putting k and temperature T into Eq. (3), E and A were obtained through the linear relationship of lnk and T–1. k = A exp(–E/RT) (2)


Fig. 1. Schematic diagram of the fixed bed reactor system.

Table 1. Summary of G(α) equations for different reaction mechanisms.

Reaction mechanism G(α) Symbol One-dimensional diffusion α2 D1 Two-dimensional diffusion (1 – α)ln(1 – α) + α D2 Three-dimensional diffusion (Jandar function) [1 – (1 – α)1/3]2 D3 Three-dimensional diffusion (G-B function) 1 – 2α/3 – (1 – α)2/3 D4 First-order chemical reaction –ln(1 – α) C1 Second-order chemical reaction (1 – α)–1 – 1 C2 Avrami–Erofe’ev random nucleation and subsequence growth (n = 2) [–ln(1 – α)]1/2 A2 Avrami–Erofe’ev random nucleation and subsequence growth (n = 3) [–ln(1 – α)]1/3 A3 Phase boundary reaction (n = 2) 1 – (1 – α)1/2 R2 Phase boundary reaction (n = 3) 1 – (1 – α)1/3 R3 Mampel power law (n = 1) α P1 Mampel power law (n = 2) α1/2 P2 Mampel power law (n = 3) α1/3 P3 Mampel power law (n = 4) α1/4 P4

dα/dt = k(α) f(α) (3)

exp( ) ( )E

d dt A fRT

(4)

0 0

( ) ( ) expt

G f d A E RT dt kt

(5)

Different reaction mechanisms (Halikia et al., 1998; Pineau

et al., 2006; Perkins et al., 2007; Pineau et al., 2007; Li et al., 2009) was used to obtain expressions of G(α), summarized in Table 1. Fourteen kinetic equations are divided into five

groups: the diffusion controlled, chemical reaction controlled, random nucleation and subsequent growth of nuclei models, boundary-controlled, and Mampel power law models. By analyzing some curve points in the set range of conversion, we can choose the best fitting model using the least square method. RESULTS AND DISCUSSION Thermodynamic Investigation

The Gibbs free energy minimization method was used to study thermodynamic of manganese oxides for the CLAS


process. Fig. 2 shows the O2 release for MnO2 and Mn2O3 for CLAS as a function of the temperature. The release of O2 is assumed to be rapid under any conditions. From Fig. 2, it can be observed that, for MnO2 and Mn2O3, the increasing temperatures promote the O2 release. The lowest oxygen releasing temperature is about 290°C and 780°C for MnO2 and Mn2O3, respectively, under inert atmosphere. The required temperatures are much lower than the reaction of CuO into Cu2O. For example, the minimum oxygen releasing temperature for the reaction of Co3O4 into CoO is 918°C and of CuO into Cu2O is 1048°C (Wang et al., 2013). The low operation temperature can decrease the energy intensity and the operation difficulty of CLAS. Non-Isothermal Experimental Studies

Conversion (α) versus time during the O2 release is presented in Fig. 3. The decomposition in Ar takes place mainly in two stages. In the first stage, the thermal decomposition of MnO2 to Mn2O3 and O2 takes place below 700°C, as indicated by a peak at 645°C. XRD patterns show

that the phases in Mn-based oxygen carriers were only MnO2, Mn2O3 and Mn3O4 (Fig. 4). It is indicated that two O2 release reactions can be described by Eqs. (6) and (7). The kinetics of these reactions has been determined in the following part. It is found that the main phases in Mn-based oxygen carriers are only MnO2 before O2 release reaction (Eq. (6)). However, the main phases in the reduced oxygen carriers are only Mn2O3. The results show that the MnO2 has been completely reduced to Mn2O3 in the O2 release reaction. The second stage is the decomposition of Mn2O3 to Mn3O4 and formation of O2. The peak is at 935°C and the decomposition is complete at 1000°C. Similarly, XRD patterns show that the main phases in the initial samples are only Mn2O3 before O2 release reaction (Eq. (7)), but the main phases in the reduced samples are only Mn3O4. It is indicated that Mn2O3 has been completely reduced to Mn3O4 in the O2 release reaction.

1 1

23 2

42 2MnO Mn O O (6)

Fig. 2. Equilibrium calculations for O2 release for MnO2 and Mn2O3 at elevated temperatures.

Fig. 3. The conversion of Mn-based oxygen carrier versus time during the O2 release.


Fig. 4. X-ray diffraction (XRD) patterns of Mn-based oxygen carriers.

2 1

34 2

633MnO Mn O O (7)

Isothermal Kinetics MnO2

The O2 release amounts versus time for MnO2 are displayed in Fig. 5. It is found that the increase of temperature from 500 to 600°C promotes the O2 release. It is attributed to the thermodynamic limitations of MnO2/Mn2O3. Generally, the O2 release amounts (0.030, 0.049, 0.069, 0.075 and 0.072 (g O2)·(g MnO2)

–1 at 500, 520, 540, 560 and 600°C, respectively) are lower than the maximum oxygen transport capacity [0.123 (g O2)·(g MnO2)

–1] for the MnO2/Mn2O3 system (Wang et al., 2013). Once the release amount of O2 is close to the equilibrium value, a dense oxygen zone surrounding OC can produce diffusion effect, which restrains the release of O2. Similar trends were also found for the Co-based and Cu-based oxygen carriers (Li et al., 2008; Song et al., 2014). Our findings are in agreement with the results for Mn–Fe oxides (Azimi et al., 2013).

As mentioned above, Eq. (5) has been from analyzing the O2 release kinetics. It presents the correlation that a possible reaction mechanism, G(α) in Table 1 and time t should follow. The most adequate G(α) can be obtained for the O2 release from an isothermal experiment. Table 1 demonstrated G(α) equations for the O2 release on the basis of fourteen mechanisms. Meanwhile, Table 2 also presented the R2 values of the least-squares linear fitting for those mechanisms in the temperature range of 500 to 600°C

From Table 2, it can be found that the first-order chemical reaction, i.e., C1, showed better overall fitting results than others in the temperature range of 500–600°C for the O2 release. The reaction rate constant (k) was then obtained from the C1 model. Considering that, for the O2 release process, the value of k is determined by the slope from fitting the C1 model with time t.

The C1 is associated with the first-order oxygen release reaction. It is assumed that C1 depends on the concentration of only one reactant (a unimolecular reaction). Therefore, it can be calculated through Eq. (8). It shows that a plot of ln (1 – α) versus t would be linear with a slope of k and an intercept of zero. Therefore, the O2 uncoupling of MnO2 is a reaction that proceeds at a rate that depends linearly only on the concentration of MnO2. The rate at which MnO2 is consumed in a first-order process is proportional to its concentration in this case. Therefore, there is no induction period during the uncoupling of MnO2, as shown in Fig. 5.

–ln(1 – α) = kt (8)

Fig. 6 shows the fittings results between the C1 model and time (t) for the typical tests at 500, 520, 540, 560 and 600°C. The reaction rate constants were acquired from the slope values. Then an Arrhenius type of plot is constructed in Fig. 7. Therefore, pre-exponential factor A and activation energy E were determined from the slope and intercept of the plot in Fig. 7. Thus, the O2 release process is expressed by an apparent pre-exponential factor A=7.92 × 104 s–1 and activation energy of 130 kJ mol–1 in the temperature range of 500–600°C. In addition, a diffusion effect from MnO2 thermodynamic properties may not be neglected. According to the thermodynamic results (Fig. 3), the equilibrium oxygen release amount will rise from 0.044 to 0.070 (g O2)·(g MnO2)

–1 (i.e., about 1.6 times higher) with the increasing

from 500 to 600°C. For the O2 release, the equilibrium O2 release amount cannot be reached. Although the gas flow rate (300 mL min–1) is chosen as high as possible for the tests to diminish the diffusion effect, the equilibrium can still be obtained at the boundaries surrounding the unreacted grains inside the MnO2 particles. The O2 release rate will be effectively decreased once the equilibrium is reached because of the higher transfer resistance for the generated oxygen,


viz., and diffusion effect. But the increasing temperature reduces the diffusion effect because of the raise in the equilibrium amounts of O2 release. In addition, the ball mill method causes the agglomeration of the active metal oxide in MnO2, in particular, for higher temperatures, leading to a

sintering of the grain. Consequently, the reduction reaction restrains the oxygen diffusion, which is reflected by the significant decrease of activation energy. As shown in Fig. 8, the typical prediction results (solid line) for MnO2 at temperatures of 500, 520, 540, 560 and 600°C, along with

Fig. 5. The O2 release amounts as a function of time based on the MnO2 conversion.

Table 2. R2 values for fitting different reaction mechanisms based on the MnO2 conversion during the O2 release.

T(°C) D1 D2 D3 D4 C1 C2 A2 A3 R2 R3 P1 P2 P3 P4 500 0.9685 0.9631 0.9570 0.9611 0.9995 0.9991 0.9649 0.9328 0.9987 0.9990 0.9973 0.9566 0.9250 0.9046520 0.9870 0.9810 0.9727 0.9784 0.9983 0.9990 0.9590 0.9282 0.9950 0.9963 0.9901 0.9438 0.9147 0.8968540 0.9957 0.9903 0.9792 0.9872 0.9983 0.9935 0.9588 0.9285 0.9914 0.9942 0.9806 0.9324 0.9059 0.8903560 0.9965 0.9946 0.9859 0.9925 0.9973 0.9909 0.9618 0.9361 0.9879 0.9917 0.9740 0.9326 0.9118 0.8998600 0.9886 0.9822 0.9712 0.9789 0.9971 0.9853 0.9846 0.9709 0.9957 0.9966 0.9911 0.9706 0.9584 0.9511

AVGa 0.9873 0.9822 0.9732 0.9796 0.9981 0.9936 0.9658 0.9393 0.9937 0.9956 0.9866 0.9472 0.9232 0.9085a: AVG = Average value.

Fig. 6. Plots for the reaction rate constant k determination from C1 model for MnO2.


Fig. 7. Arrhenius plot for MnO2 during the O2 release.

Fig. 8. OC conversion versus time for MnO2 during the O2 release.

experimental data (dot points). There is an excellent agreement between the theoretical predicted and experiment values for all temperatures. Mn2O3

The O2 release amounts versus time for MnO2 are displayed in Fig. 8. The O2 release amounts raised with increasing the temperature from 760 to 820°C. It is indicated that the higher temperature promote the O2 release because of the thermodynamic limitations of Mn2O3/Mn3O4. Generally, the O2 release amounts [0.018, 0.022, 0.023, 0.025 and 0.025 (g O2)·(g Mn2O3)

–1] are lower than the maximum oxygen transport capacity [0.034 (g O2)·(g Mn2O3)

–1] for the Mn2O3/Mn3O4 system (Wang et al., 2013).Table 3 shows that the Avrami–Erofe’ev random nucleation and subsequence growth model with n=2 (A2), attain better

fitting than other models for the O2 release. k was then determined from the A2 model for the O2 release. For the O2 release process, the value of k is obtained by the slope from fitting the A2 model with time t.

The A2 is associated with two-dimensional growth of nuclei. Assumptions are made regarding the rate of change in the number of nuclei and the volume swept out by them as they react. Therefore, it can be written in logarithmic form as Eq. (9). Mn3O4 nuclei may be present initially or they may grow in at certain locations by a process that is usually considered to be first order. It suggests that (i) Mn3O4 particles will be nucleated and precipitated out from the Mn(O) intermediate/complex during heating and (ii) the growth of the fine nuclei of Mn3O4 particles will be restricted to the surface only (two dimensional growth).


Table 3. R2 values for fitting different reaction mechanisms based on the Mn2O3 conversion during the O2 release.

T(°C) D1 D2 D3 D4 C1 C2 A2 A3 R2 R3 P1 P2 P3 P4 760 0.8260 0.8205 0.8149 0.8186 0.9601 0.9533 0.9996 0.9938 0.9633 0.9623 0.9662 0.9995 0.9925 0.9841770 0.8560 0.8476 0.8386 0.8446 0.9666 0.9558 0.9993 0.9925 0.9712 0.9697 0.9753 0.9986 0.9902 0.9817780 0.8741 0.8652 0.8557 0.8620 0.9718 0.9608 0.9995 0.9946 0.9764 0.9749 0.9804 0.9989 0.9927 0.9865800 0.9115 0.9031 0.8940 0.9001 0.9820 0.9729 0.9998 0.9972 0.9856 0.9845 0.9888 0.9994 0.9958 0.9925820 0.9071 0.8951 0.8816 0.8906 0.9717 0.9549 0.9984 0.9996 0.9782 0.9762 0.9836 0.9983 0.9989 0.9974

AVG 0.8749 0.8663 0.8570 0.8632 0.9704 0.9595 0.9993 0.9955 0.9749 0.9735 0.9789 0.9989 0.9940 0.9884

Fig. 9. The O2 release amount as a function of time based on the Mn2O3 conversion.

Fig. 10. Plots for the reaction rate constant k determination from A2 model for Mn2O3.

[–ln(1 – α)]1/2 = kt (9)

Fig. 9 shows the fittings between the A2 model and t for the typical tests performed at 760, 770, 780, 800 and 820°C. The corresponding slope values were obtained for k. Then we construct an Arrhenius type of plot, as shown in

Fig. 10. As a result, A and E can be obtained from the slope and intercept of the plot (Fig. 10).

Given all that, There is an E of 163 kJ mol–1 with A = 7.87 × 104 s–1 during the O2 release process in the temperature range of 760–820°C. As shown in Fig. 3, the oxygen release amounts are higher than those of the corresponding


Fig. 11. Arrhenius plot for Mn2O3 during the O2 release.

Fig. 12. OC conversion versus time for Mn2O3 during the O2 release.

equilibrium values, because the gas flow rate is chosen as high as possible for the tests to diminish the diffusion effect. Once the equilibrium is broken through, the O2 release rate will be significantly increased.

Fig. 12 shows the typical prediction values (solid line) for Mn2O3 conversion during the O2 release at temperatures of 760, 770, 780, 800 and 820°C, along with experimental data (dot points). There is an excellent agreement between the theoretical predicted and experimental values for all temperatures. CONCLUSIONS

In this work, reaction mechanisms have been identified for the O2 release reaction of MnO2 and Mn2O3. The O2

release behavior was investigated under Ar in a fixed bed reactor. The typical experimental conditions, viz., gas flow rate (300 mL min–1), sample loading (500 mg), and average particle size (100 µm), have been chosen for experiment to obtain the corresponding kinetic parameters. It is found that the O2 release amounts raise significantly with increasing the temperature. The O2 release mechanisms have been identified for MnO2 and Mn2O3. Results indicate that the first-order chemical reaction model (C1) and Avrami–Erofe’ev random nucleation and subsequence growth model (A2) are appropriate for the O2 release of MnO2 and Mn2O3, respectively. For MnO2, the pre-exponential factor and activation energy were determined as 7.92 × 104 s–1 and 130 kJ mol–1, respectively. For Mn2O3, the pre-exponential factor and activation energy are 7.87 × 104 s–1 and 163 kJ mol–1, respectively.


ACKNOWLEDGMENTS

This work was supported by Natural Science Foundation of Jiangsu province with Grant No. BK2012406, National Natural Science Foundation of China with Grant No. 21206074, Research Fund for the Doctoral Program of Higher Education of China with Grant No. 20123219120033, China Postdoctoral Science Foundation Funded Project with Grant No. 2014M561649, the Fundamental Research Funds for the Central Universities with Grant No. 30920140112004, and Zijin Intelligent Program of Nanjing University of Science and Technology with Grant No. 2013-ZJ-0103. REFERENCES Adánez-Rubio, I., Gayán, P., Abad, A., de Diego, L.F.,

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Received for review, July 16, 2014 Revised, January 26, 2015

Accepted, July 20, 2015

o2 release of mn-based oxygen carrier for chemical ...(schreiber et al., 2013), pressure swing...

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