- Email: [email protected]
Thermochemical Conversion of CO2 into Solar Fuels Using Ferrite Nanomaterials
Mohammed Jaber F. Al Marri and Fadwa El Jack (Editors), Proceedings of the 4th International Gas Processing Symposium, October 26–27, 2014 , Doha, Qatar. © 2015 Elsevier B.V. All rights reserved.
Thermochemical Conversion of CO2 into Solar Fuels Using Ferrite Nanomaterials Rahul R. Bhosale,a,* Dareen Dardor,a Shahd S. Gharbia,a Jamila Folady,a Mehak Jilani,a Anand Kumar,a Leo L. P. van den Broeke,a Fangjian Lin,b Ivo Alxneitb a Department of Chemical Engineering, College of Engineering, Qatar University, PO Box 2713, Doha, Qatar. b Solar Technology Laboratory, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland. *Corresponding Author: [email protected]
Abstract This paper reports the synthesis of NixFe3-xO4 nanoparticles via sol-gel method. For NixFe3-xO4 synthesis, the Ni and Fe precursor salts were dissolved in ethanol and propylene oxide (PO) was added dropwise to the well mixed solution achieve gel formation. As-prepared gels were aged, dried and subsequently calcined upto 600oC in air. The calcined powders were characterized by powder x-ray diffractometer (XRD), BET surface area, as well as scanning (SEM) and transmission (TEM) electron microscopy. The derived NixFe3-xO4 nanoparticles were further examined towards thermochemical conversion of CO2 into solar fuels by performing several reduction/re-oxidation cycles using a thermogravimetric analyzer (TGA). Keywords: Solar Fuels, CO2 Conversion, Sol-Gel Method, Ferrites, Nanomaterial, and Thermochemical Reactions 1. Introduction The extensive utilization of fossil fuels led to a rapid depletion of the easily accessible oil reserves resulting in continuously rising oil prices. Furthermore, combustion of fossil fuels is believed to be one of the major causes of increase in the CO2 concentration level in the environment. The increase in CO 2 emission into the environment is of serious concern for future because of CO 2 being a major contributor to the greenhouse gases [1-2]. Since the atmospheric concentration of CO2 is shown to directly affect the climate temperature [3 -4], search for carbon neutral
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alternative energy sources is growing along with ways to reduce the atmospheric CO 2 concentration. To overcome the problems related to the continuously rising of oil prices and global warming due to the CO2 induced greenhouse effect, as one of the promising alternatives, the liberated CO 2 can be re-energized into CO via metal oxide (MO) based thermochemical looping process using concentrated solar energy. The C O produced via solar thermochemical CO 2-splitting can be combined with H2 derived from MO based solar thermochemical H 2O-splitting process to produce solar syngas which can be further processed to liquid fuels such as methanol, diesel, and jet fuel via the Fischer-Tropsch process [5]. Production of solar fuels via MO based thermochemical reactions is a two-step process. In the first step, the MO is reduced into a lower valence MO or metal with the help of solar energy. The reduced MO is further re-oxidized in the second step via H2O and/or CO2 splitting reactions. Among the many MOs investigated so far for solar fuel production, in recent years, research has been focused towards non-volatile mixed MOs such as ferrites [6-19]. Ferrites are particularly appealing as their reduced form is a solid and hence the separation of a gaseous metal (or MO) and O 2, a challenging and compulsory step in cycles based on ZnO/Zn or SnO2/SnO/Sn, can be eliminated. Previously, ferrites were considerably used for solar H 2 production [6-16], while their utilization for solar CO or syngas production is very limited [17-19]. In this paper, synthesis of NixFe3-xO4 (where, x = 0.2 to 1) nanoparticles using sol-gel method is presented. Sol-gel synthesized powders were further characterized by using powder x-ray NixFe3-xO4 diffractometer (XRD), BET surface area analyzer, scanning (SEM) and transmission electron microscopy (TEM), and an inductively coupled plasma spectrometer (ICP). Furthermore, NixFe3-xO4 powders were examined towards their thermal reduction and CO 2 splitting ability by performing successive thermochemical cycles using a thermogravimetric analyzer (TGA). A typical Ni xFe3-xO4 based two-step solar thermochemical CO2 splitting process is depicted in Figure 1.
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Figure 1. NixFe3-xO4 based solar thermochemical CO2 splitting process.
2. Experimental 2.1 Synthesis of NixFe3-xO4
For the synthesis of NixFe3-xO4 via sol-gel method, the nitrate salts of Ni and Fe were added in ethanol and this mixture was sonicated to dissolve the metal salts in the solvent. To this solution obtained after sonication, predetermined amount of propylene oxide (PO) was added dropwise and the gel formation was achieved. For instance, a picture of a typical NixFe3-xO4 gel prepared via sol-gel method is shown in Figure 2. As-prepared gels were aged for 24 h, dried at 100oC, and then heated up to 600oC and cooled down rapidly in air. Various combinations of NixFe3-xO4 were synthesized such as Ni0.2Fe2.8O4 (NF2), Ni0.4Fe2.6O4 (NF4), Ni0.5Fe2.5O4 (NF5), Ni0.6Fe2.4O4 (NF6), Ni0.8Fe2.2O4 (NF8), and NiFe2O4 (NF10).
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Figure 2. NixFe3-xO4 gel synthesized via sol-gel method. 2.2 Characterization of Ni xFe3-xO4
Phase purity, crystallite size, morphology, specific surface area, and elemental composition of the sol-gel derived ferrite powders were analyzed using a Panalytical XPert MPD/DY636 powder X-ray diffractometer, a Zeiss Supra 55VP field-emission scanning electron microscope (SEM), a FEI – Tecnai G2 200kV transmission electron microscope (TEM), a BET surface area analyzer (Micromeritics, ASAP 2420), and an ICP (Thermo, iCAP 6500). 2.3 Thermochemical CO2 Splitting Set-ups and Operating Procedure
Thermal reduction and CO2 splitting ability of the sol-gel derived NixFe3-xO4 materials was examined by using a thermogravimetric analyzer (TGA, Netzsch STA 409). Approximately 50 mg of ferrite powder was placed inside an Al2O3 crucible and was subjected to multiple thermal reduction (1400oC) and CO2 splitting (1000oC) cycles. During the thermal reduction step, the ferrite powder was heated upto 1400oC and maintained at this temperature for 60 min in an inert Ar atmosphere (100 ml/min). The mass loss observed after 1000oC was directly correlated towards O2 released by the ferrite material due to the thermal reduction. Once the thermal reduction was carried out for 1h, the temperature was lowered to 1000oC to perform the CO2 splitting reaction. CO2 was injected (100 ml/min, Ar : CO2 = 1:1) once the targeted reaction temperature was reached and the CO2 splitting reaction was performed at isothermal conditions for 30 min. The variation in the mass of the sample was directly correlated to the O2 release (mass loss) during thermal reduction step or to CO produced
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(mass gain) during the CO2 splitting step. Furthermore, the gases exiting the TGA were continuously analyzed via a gas chromatograph (GC, VARIAN, CP-4900, Micro GC 2 channel system).
3. Results and Discussion
Intensity Counts (a.u.)
The compositional purity of the synthesized Ni x Fe3-xO4 materials was analyzed using a powder XRD and the corresponding XRD patterns are shown in Figure 3. Sol-gel derived Nix Fe3-xO4 materials indicate strong reflections and a well-defined spinel cubic structure with high degree of crystallinity. Reflections that could be attributed to impurities such as precursors, NiO, or metallic Ni were absent which further confirm the formation of phase pure NixFe3-xO4 materials. Due to the substitution of the Ni ions in the Fe3O4 spinel structure, a successive shift in the diffraction patterns of the NixFe3-xO4 materials was observed. The elemental composition of the synthesized NixFe3-xO4 materials was further confirmed with the help of ICP analysis.
NF10 NF8 NF6 NF5 NF4 NF2
2θ Figure 3. XRD patterns of sol-gel derived Nix Fe3-x O4. Size of the single crystalline domains of sol-gel derived NixFe3-xO4 redox materials were calculated by using Scherrer equation. This quantitative analysis indicate slight decrease in the crystallite size of the Ni xFe3-xO4 with the increase in the degree of substitution of Ni in the ferrite spinel structure. Typically, the crystallite size for different Ni xFe3-xO4 materials was observed to be in the range 24 to 34 nm. The SEM and TEM analysis further confirm the nanoparticle morphology of the sol -gel derived NixFe3-xO4 materials. As an example, SEM and TEM pictures of NF10 are shown in Figure 4. The
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specific surface area of the sol -gel derived NixFe3-xO4 obtained after calcination at 600oC was observed to be in the range of 35 to 40 m2/g. Thermochemical CO production ability of the derived Ni xFe3-xO4 redox materials was investigated by performing multiple thermal reduction and CO2-splitting cycles using a high temperature thermogravimetric analyzer. Befor performing the thermochemical experiments by using the derived NixFe3-xO4 materials, a baseline run was conducted under identical experimental conditions in absence of the ferrite powder (using empty Al2O3 crucible). This allows subtracting artifacts due to buoyancy effects or caused by changing the gas composition.
a)
b)
20 nm
Figure 4. a) SEM and b) TEM image of sol-gel derived NF10 redox material.
Figure 5. CO2 -splitting experiments performed using sol-gel derived NF8.
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Thermal reduction and thermochemical CO 2 -splitting ability of the sol-gel derived Nix Fe3-xO4 materials was examined by performing four successive thermochemical cycles in the temperature range of 1000 oC to 1400o C. For instance, the thermogravimetric mass loss during thermal reduction step and as gain during CO2 -splitting step in case of NF8 material is shown in Figure 5. The temperature is reported as blue line while the weight change of the NF8 sample is reported in red color. As shown in Figure 5, the redox capacity of the NF8 material does not deteriorate i.e. approximately the same mass loss and mass gain is observed in all cycles. During first th e r ma l reduction step, a disproportionally large weight loss occurs due to the desorption of physisorbed water from the NF8 sample According to the results obtained via TGA experiments, the % mass loss during the 1st thermal reduction step was much higher in case of NF2, NF4, and NF5 as compared to the other Ni xFe3-xO4 materials. However, the thermal reduction ability of NF10 (% mass loss) was observed to be the highest and constant during the 2 nd, 3rd, and 4th thermochemical cycles. Likewise, the re - oxidation ability (% mass gain) was again observed to be maximum in case of NF10 material as compared to other NixFe3-xO4 materials. The average thermal reduction and CO 2-splitting ability of the derived NixFe3-xO4 redox materials during 2 nd, 3rd, and 4th thermochemical cycles was observed to be in the order of NF10 > NF8 > NF6 > NF5 > NF4 > NF2. The obtained results indicate that the NF10 material performs best when compared with the other sol-gel derived NixFe3-xO4 materials and also with ceria based redox materials investigated previously [20-23]. 4. Conclusions In this investigation, Ni x Fe3-xO4 (where, x = 0.2 to 1) redox materials were successfully synthesized via sol -gel method by using nitrate salts of Ni, and Fe, ethanol as solvent, and PO as gelation agent. The XRD analysis confirms the phase pure formation of Ni xFe3x O4 materials with high degree of dopant incorporation in the ferrite spinel structure and with no impurities. Quantitative XRD and SEM/TEM analysis reveal nanocrystalline morphology of the derived Ni xFe3-xO4. Assynthesized ferrite powders were further investigated for their use in thermochemical CO2 -splitting and thermal reduction cycles in the temperature range 1000 oC to 1400oC using a Thermogravimetricv analyzer. The results obtained indicate that the stoichiometric NiFe 2 O4 (NF10) generates the highest amounts of O 2 and CO when compared to the other ferrites examined in this study and other nonvolatile redox materials such as ceria based oxides investigated previously.
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5. Acknowledgements The authors gratefully acknowledge the financial support provided by the Qatar University Internal Grant (QUUG-CENG-CHE-13/14-4), Indo-Swiss Joint Research Program (ISJRP, grant #138852), and the Swiss Federal Office of Energy (SFOE). References
(1) Bhosale, R., Mahajani, V., Sep. Sci. Technol., 48 (2013) 2324. (2) Bhosale, R., Mahajani, V., J. Renewable Sustainable Energy, 5 (2013) 063110-1. (3) Woods Hole Research Center, http://www.whrc.org/resources/primer.html
(2014) last accessed May 16, 2014.
(4) US Environment Protection Agency, http://epa.gov/climatechange (2014) last (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23)
accessed May 16, 2014. Steinfeld, A. Sol. Energy, 78 (2005) 603. Kodama, T., Gokon, N., Yamamoto, R., Sol. Energy, 82 (2008) 73. Scheffe, J., Li, J., Weimer, A., Int. J. Hydrogen Energy 35 (2010) 3333. Roeb, M., Gathmann, N., Neises, M., Sattler, C., Pitz-Paal, R., Int. J. Hydrogen Energy 33 (2009) 893. Lorentzou, S., Agrafiotis, C., Konstandopoulos, A., Granular Matter 10 (2008) 113. Varsano, F., Padella, F., Alvani, C., Bellusci, M., La Barbera, A., Int. J. Hydrogen Energy 37 (2012) 11595. Bhosale, R., Shende, R., Puszynski, J., J. Energy Power Eng. 4 (2010) 27. Bhosale, R., Shende, R., Puszynski, J., Int. Rev. Chem. Eng. 2 (2010) 852. Bhosale, R., Shende, R., Puszynski, J., Int. J. Hydrogen Energy 2 (2012) 2924. Bhosale, R., Khadka, R., Shende, R., Puszynski, J., J. Renewable Sustainable Energy 3 (2011) 063104 – 1. Bhosale, R., Shende, R., Puszynski, J., J. Renewable Sustainable Energy 3 (2011) 063104 – 1. Shende, R., Puszynski, J., Opoku, M., Bhosale, R., NSTI-Nanotech Conference & Expo. Proc. ISBN 978-1-4398-1782-7 (2009). Stenger, S., Neises, M., Roeb, M., Sattler, C., Energy Techol. TMS (2011). Allen. K., Auyeung, N., Rahmatian, N., Klausner, J., Coker, E., JOM 65 (2013) 1682. Allen. K., Coker, E., Auyeung, N., Klausner, J., JOM 65 (2013) 1670. Kang, M., Wu, X., Zhang, J., Zhao, N., Wei, W., Sun, Y., RSC Advances 4 (2014) 5583. Jiang, Q., Zhou, G., Jiang, Z., Li, C., Sol. Energy 99 (2014) 55. Kang, M., Zhang, J., Wang, C., Wang, F., Zhao, N., Xiao, F., Wei, W., Sun, Y., RSC Advances 3 (2013) 18878. Abanades, S., Gal, A. L., Fuel 102 (2012) 180.
Thermochemical Conversion of CO2 into Solar Fuels Using Ferrite Nanomaterials Rahul R. Bhosale,a,* Dareen Dardor,a Shahd S. Gharbia,a Jamila Folady,a Mehak Jilani,a Anand Kumar,a Leo L. P. van den Broeke,a Fangjian Lin,b Ivo Alxneitb a Department of Chemical Engineering, College of Engineering, Qatar University, PO Box 2713, Doha, Qatar. b Solar Technology Laboratory, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland. *Corresponding Author: [email protected]
Abstract This paper reports the synthesis of NixFe3-xO4 nanoparticles via sol-gel method. For NixFe3-xO4 synthesis, the Ni and Fe precursor salts were dissolved in ethanol and propylene oxide (PO) was added dropwise to the well mixed solution achieve gel formation. As-prepared gels were aged, dried and subsequently calcined upto 600oC in air. The calcined powders were characterized by powder x-ray diffractometer (XRD), BET surface area, as well as scanning (SEM) and transmission (TEM) electron microscopy. The derived NixFe3-xO4 nanoparticles were further examined towards thermochemical conversion of CO2 into solar fuels by performing several reduction/re-oxidation cycles using a thermogravimetric analyzer (TGA). Keywords: Solar Fuels, CO2 Conversion, Sol-Gel Method, Ferrites, Nanomaterial, and Thermochemical Reactions 1. Introduction The extensive utilization of fossil fuels led to a rapid depletion of the easily accessible oil reserves resulting in continuously rising oil prices. Furthermore, combustion of fossil fuels is believed to be one of the major causes of increase in the CO2 concentration level in the environment. The increase in CO 2 emission into the environment is of serious concern for future because of CO 2 being a major contributor to the greenhouse gases [1-2]. Since the atmospheric concentration of CO2 is shown to directly affect the climate temperature [3 -4], search for carbon neutral
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alternative energy sources is growing along with ways to reduce the atmospheric CO 2 concentration. To overcome the problems related to the continuously rising of oil prices and global warming due to the CO2 induced greenhouse effect, as one of the promising alternatives, the liberated CO 2 can be re-energized into CO via metal oxide (MO) based thermochemical looping process using concentrated solar energy. The C O produced via solar thermochemical CO 2-splitting can be combined with H2 derived from MO based solar thermochemical H 2O-splitting process to produce solar syngas which can be further processed to liquid fuels such as methanol, diesel, and jet fuel via the Fischer-Tropsch process [5]. Production of solar fuels via MO based thermochemical reactions is a two-step process. In the first step, the MO is reduced into a lower valence MO or metal with the help of solar energy. The reduced MO is further re-oxidized in the second step via H2O and/or CO2 splitting reactions. Among the many MOs investigated so far for solar fuel production, in recent years, research has been focused towards non-volatile mixed MOs such as ferrites [6-19]. Ferrites are particularly appealing as their reduced form is a solid and hence the separation of a gaseous metal (or MO) and O 2, a challenging and compulsory step in cycles based on ZnO/Zn or SnO2/SnO/Sn, can be eliminated. Previously, ferrites were considerably used for solar H 2 production [6-16], while their utilization for solar CO or syngas production is very limited [17-19]. In this paper, synthesis of NixFe3-xO4 (where, x = 0.2 to 1) nanoparticles using sol-gel method is presented. Sol-gel synthesized powders were further characterized by using powder x-ray NixFe3-xO4 diffractometer (XRD), BET surface area analyzer, scanning (SEM) and transmission electron microscopy (TEM), and an inductively coupled plasma spectrometer (ICP). Furthermore, NixFe3-xO4 powders were examined towards their thermal reduction and CO 2 splitting ability by performing successive thermochemical cycles using a thermogravimetric analyzer (TGA). A typical Ni xFe3-xO4 based two-step solar thermochemical CO2 splitting process is depicted in Figure 1.
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Figure 1. NixFe3-xO4 based solar thermochemical CO2 splitting process.
2. Experimental 2.1 Synthesis of NixFe3-xO4
For the synthesis of NixFe3-xO4 via sol-gel method, the nitrate salts of Ni and Fe were added in ethanol and this mixture was sonicated to dissolve the metal salts in the solvent. To this solution obtained after sonication, predetermined amount of propylene oxide (PO) was added dropwise and the gel formation was achieved. For instance, a picture of a typical NixFe3-xO4 gel prepared via sol-gel method is shown in Figure 2. As-prepared gels were aged for 24 h, dried at 100oC, and then heated up to 600oC and cooled down rapidly in air. Various combinations of NixFe3-xO4 were synthesized such as Ni0.2Fe2.8O4 (NF2), Ni0.4Fe2.6O4 (NF4), Ni0.5Fe2.5O4 (NF5), Ni0.6Fe2.4O4 (NF6), Ni0.8Fe2.2O4 (NF8), and NiFe2O4 (NF10).
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Figure 2. NixFe3-xO4 gel synthesized via sol-gel method. 2.2 Characterization of Ni xFe3-xO4
Phase purity, crystallite size, morphology, specific surface area, and elemental composition of the sol-gel derived ferrite powders were analyzed using a Panalytical XPert MPD/DY636 powder X-ray diffractometer, a Zeiss Supra 55VP field-emission scanning electron microscope (SEM), a FEI – Tecnai G2 200kV transmission electron microscope (TEM), a BET surface area analyzer (Micromeritics, ASAP 2420), and an ICP (Thermo, iCAP 6500). 2.3 Thermochemical CO2 Splitting Set-ups and Operating Procedure
Thermal reduction and CO2 splitting ability of the sol-gel derived NixFe3-xO4 materials was examined by using a thermogravimetric analyzer (TGA, Netzsch STA 409). Approximately 50 mg of ferrite powder was placed inside an Al2O3 crucible and was subjected to multiple thermal reduction (1400oC) and CO2 splitting (1000oC) cycles. During the thermal reduction step, the ferrite powder was heated upto 1400oC and maintained at this temperature for 60 min in an inert Ar atmosphere (100 ml/min). The mass loss observed after 1000oC was directly correlated towards O2 released by the ferrite material due to the thermal reduction. Once the thermal reduction was carried out for 1h, the temperature was lowered to 1000oC to perform the CO2 splitting reaction. CO2 was injected (100 ml/min, Ar : CO2 = 1:1) once the targeted reaction temperature was reached and the CO2 splitting reaction was performed at isothermal conditions for 30 min. The variation in the mass of the sample was directly correlated to the O2 release (mass loss) during thermal reduction step or to CO produced
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(mass gain) during the CO2 splitting step. Furthermore, the gases exiting the TGA were continuously analyzed via a gas chromatograph (GC, VARIAN, CP-4900, Micro GC 2 channel system).
3. Results and Discussion
Intensity Counts (a.u.)
The compositional purity of the synthesized Ni x Fe3-xO4 materials was analyzed using a powder XRD and the corresponding XRD patterns are shown in Figure 3. Sol-gel derived Nix Fe3-xO4 materials indicate strong reflections and a well-defined spinel cubic structure with high degree of crystallinity. Reflections that could be attributed to impurities such as precursors, NiO, or metallic Ni were absent which further confirm the formation of phase pure NixFe3-xO4 materials. Due to the substitution of the Ni ions in the Fe3O4 spinel structure, a successive shift in the diffraction patterns of the NixFe3-xO4 materials was observed. The elemental composition of the synthesized NixFe3-xO4 materials was further confirmed with the help of ICP analysis.
NF10 NF8 NF6 NF5 NF4 NF2
2θ Figure 3. XRD patterns of sol-gel derived Nix Fe3-x O4. Size of the single crystalline domains of sol-gel derived NixFe3-xO4 redox materials were calculated by using Scherrer equation. This quantitative analysis indicate slight decrease in the crystallite size of the Ni xFe3-xO4 with the increase in the degree of substitution of Ni in the ferrite spinel structure. Typically, the crystallite size for different Ni xFe3-xO4 materials was observed to be in the range 24 to 34 nm. The SEM and TEM analysis further confirm the nanoparticle morphology of the sol -gel derived NixFe3-xO4 materials. As an example, SEM and TEM pictures of NF10 are shown in Figure 4. The
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specific surface area of the sol -gel derived NixFe3-xO4 obtained after calcination at 600oC was observed to be in the range of 35 to 40 m2/g. Thermochemical CO production ability of the derived Ni xFe3-xO4 redox materials was investigated by performing multiple thermal reduction and CO2-splitting cycles using a high temperature thermogravimetric analyzer. Befor performing the thermochemical experiments by using the derived NixFe3-xO4 materials, a baseline run was conducted under identical experimental conditions in absence of the ferrite powder (using empty Al2O3 crucible). This allows subtracting artifacts due to buoyancy effects or caused by changing the gas composition.
a)
b)
20 nm
Figure 4. a) SEM and b) TEM image of sol-gel derived NF10 redox material.
Figure 5. CO2 -splitting experiments performed using sol-gel derived NF8.
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Thermal reduction and thermochemical CO 2 -splitting ability of the sol-gel derived Nix Fe3-xO4 materials was examined by performing four successive thermochemical cycles in the temperature range of 1000 oC to 1400o C. For instance, the thermogravimetric mass loss during thermal reduction step and as gain during CO2 -splitting step in case of NF8 material is shown in Figure 5. The temperature is reported as blue line while the weight change of the NF8 sample is reported in red color. As shown in Figure 5, the redox capacity of the NF8 material does not deteriorate i.e. approximately the same mass loss and mass gain is observed in all cycles. During first th e r ma l reduction step, a disproportionally large weight loss occurs due to the desorption of physisorbed water from the NF8 sample According to the results obtained via TGA experiments, the % mass loss during the 1st thermal reduction step was much higher in case of NF2, NF4, and NF5 as compared to the other Ni xFe3-xO4 materials. However, the thermal reduction ability of NF10 (% mass loss) was observed to be the highest and constant during the 2 nd, 3rd, and 4th thermochemical cycles. Likewise, the re - oxidation ability (% mass gain) was again observed to be maximum in case of NF10 material as compared to other NixFe3-xO4 materials. The average thermal reduction and CO 2-splitting ability of the derived NixFe3-xO4 redox materials during 2 nd, 3rd, and 4th thermochemical cycles was observed to be in the order of NF10 > NF8 > NF6 > NF5 > NF4 > NF2. The obtained results indicate that the NF10 material performs best when compared with the other sol-gel derived NixFe3-xO4 materials and also with ceria based redox materials investigated previously [20-23]. 4. Conclusions In this investigation, Ni x Fe3-xO4 (where, x = 0.2 to 1) redox materials were successfully synthesized via sol -gel method by using nitrate salts of Ni, and Fe, ethanol as solvent, and PO as gelation agent. The XRD analysis confirms the phase pure formation of Ni xFe3x O4 materials with high degree of dopant incorporation in the ferrite spinel structure and with no impurities. Quantitative XRD and SEM/TEM analysis reveal nanocrystalline morphology of the derived Ni xFe3-xO4. Assynthesized ferrite powders were further investigated for their use in thermochemical CO2 -splitting and thermal reduction cycles in the temperature range 1000 oC to 1400oC using a Thermogravimetricv analyzer. The results obtained indicate that the stoichiometric NiFe 2 O4 (NF10) generates the highest amounts of O 2 and CO when compared to the other ferrites examined in this study and other nonvolatile redox materials such as ceria based oxides investigated previously.
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5. Acknowledgements The authors gratefully acknowledge the financial support provided by the Qatar University Internal Grant (QUUG-CENG-CHE-13/14-4), Indo-Swiss Joint Research Program (ISJRP, grant #138852), and the Swiss Federal Office of Energy (SFOE). References
(1) Bhosale, R., Mahajani, V., Sep. Sci. Technol., 48 (2013) 2324. (2) Bhosale, R., Mahajani, V., J. Renewable Sustainable Energy, 5 (2013) 063110-1. (3) Woods Hole Research Center, http://www.whrc.org/resources/primer.html
(2014) last accessed May 16, 2014.
(4) US Environment Protection Agency, http://epa.gov/climatechange (2014) last (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23)
accessed May 16, 2014. Steinfeld, A. Sol. Energy, 78 (2005) 603. Kodama, T., Gokon, N., Yamamoto, R., Sol. Energy, 82 (2008) 73. Scheffe, J., Li, J., Weimer, A., Int. J. Hydrogen Energy 35 (2010) 3333. Roeb, M., Gathmann, N., Neises, M., Sattler, C., Pitz-Paal, R., Int. J. Hydrogen Energy 33 (2009) 893. Lorentzou, S., Agrafiotis, C., Konstandopoulos, A., Granular Matter 10 (2008) 113. Varsano, F., Padella, F., Alvani, C., Bellusci, M., La Barbera, A., Int. J. Hydrogen Energy 37 (2012) 11595. Bhosale, R., Shende, R., Puszynski, J., J. Energy Power Eng. 4 (2010) 27. Bhosale, R., Shende, R., Puszynski, J., Int. Rev. Chem. Eng. 2 (2010) 852. Bhosale, R., Shende, R., Puszynski, J., Int. J. Hydrogen Energy 2 (2012) 2924. Bhosale, R., Khadka, R., Shende, R., Puszynski, J., J. Renewable Sustainable Energy 3 (2011) 063104 – 1. Bhosale, R., Shende, R., Puszynski, J., J. Renewable Sustainable Energy 3 (2011) 063104 – 1. Shende, R., Puszynski, J., Opoku, M., Bhosale, R., NSTI-Nanotech Conference & Expo. Proc. ISBN 978-1-4398-1782-7 (2009). Stenger, S., Neises, M., Roeb, M., Sattler, C., Energy Techol. TMS (2011). Allen. K., Auyeung, N., Rahmatian, N., Klausner, J., Coker, E., JOM 65 (2013) 1682. Allen. K., Coker, E., Auyeung, N., Klausner, J., JOM 65 (2013) 1670. Kang, M., Wu, X., Zhang, J., Zhao, N., Wei, W., Sun, Y., RSC Advances 4 (2014) 5583. Jiang, Q., Zhou, G., Jiang, Z., Li, C., Sol. Energy 99 (2014) 55. Kang, M., Zhang, J., Wang, C., Wang, F., Zhao, N., Xiao, F., Wei, W., Sun, Y., RSC Advances 3 (2013) 18878. Abanades, S., Gal, A. L., Fuel 102 (2012) 180.