Screening of NiFe2O4 Nanoparticles as Oxygen Carrier in Chemical

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Screening of NiFe2O4 Nanoparticles as Oxygen Carrier in Chemical Looping Hydrogen Production Shuai Liu, Fang He, Zhen Huang, Anqing Zheng, Yipeng Feng, Yang Shen, Haibin Li, Hao Wu, and Peter Glarborg Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00284 • Publication Date (Web): 04 Apr 2016 Downloaded from http://pubs.acs.org on April 12, 2016

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Screening of NiFe2O4 Nanoparticles as Oxygen Carrier in Chemical Looping Hydrogen Production Shuai Liu1,2, Fang He*,1, Zhen Huang1, Anqing Zheng1, Yipeng Feng1, Yang Shen1, Haibin li1, Hao Wu3, and Peter Glarborg3 1

CAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion,

Chinese Academy of Sciences (CAS), Guangzhou 510640, China 2

Sino-Danish Center for Education and Research, University of Chinese Academy of

Sciences, Beijing 100049, China 3

Department of Chemical and Biochemical Engineering, Technical University of

Denmark, 2800 Kgs. Lyngby, Denmark

ACS Paragon Plus Environment

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ABSTRACT: The objective of this paper is to systematically investigate the influences of different preparation methods on the properties of NiFe2O4 nanoparticles as oxygen carrier in chemical looping hydrogen production (CLH). The solid state (SS), co-precipitation (CP), hydrothermal (HT) and sol-gel (SG) methods were used to prepare NiFe2O4 oxygen carriers. Samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) surface area measurement as well as Barrett-Joyner-Halenda (BJH) porosity test. The performance of the prepared materials was firstly evaluated in a TGA reactor through a CO reduction and subsequent steam oxidation process. Then a complete redox process was conducted in a fixed-bed reactor, where the NiFe2O4 oxygen carrier was first reduced by simulated biomass pyrolysis gas (24% H2 + 24% CO + 12% CO2 + N2 balance), then reacted with steam to produce H2, and finally fully oxidized by air. The NiFe2O4 oxygen carrier prepared by the sol-gel method showed the best capacity for hydrogen production and the highest recovery degree of lattice oxygen, in agreement with the characterization results. Furthermore, compared to individual nickel ferrite particles, the mixture of NiFe2O4 and SiO2 presented remarkable higher stability during 20 cycles in the fixed-bed reactor. The structural and morphological stability of samples after reactions was also examined by XRD, XPS and SEM analyses. KEYWORDS: Chemical looping hydrogen production (CLH), NiFe2O4 oxygen carrier, Hydrogen production capacity, Stability.


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1 INTRODUCTION

The global climate change motivates exploration of new technologies for reducing the CO2 emission from combustion of fossil fuels.1-3 Hydrogen, as a green and efficient energy source, is expected to play an important part in future energy systems.4, 5 Chemical Looping Hydrogen Production (CLH) is an attractive technology for H2 production because it can simultaneously produce H2 and capture CO2.5-7 Figure 1 shows a simplified schematic of an ideal CLH system that mainly consists of a fuel reactor, a steam reactor, and an air reactor. Metal-oxide based oxygen carriers circulate between these reactors to be repeatedly reduced and oxidized, forming a redox loop.8, 9 The metal oxide (MeOx) is first reduced in a fuel reactor, which converts fuels into CO2 and H2O. Then the reduced oxygen carrier (Me) enters a steam reactor and reacts with H2O to produce H2 and partially oxidized oxygen carrier (MeOx-1). Finally the intermediate metal oxide (MeOx-1) is oxidized completely in an air reactor to recover its initial state for recycling. Through condensation of H2O, pure CO2 and H2 can be produced from the outlets of the fuel reactor and the steam reactor respectively.8, 10, 11 Overall, metal oxides act as oxygen carrier, heat carrier and catalyst in the CLH process.8, 12


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CO2+H2O Oxygen-lean Air MeOx

Fuel reactor

Fuel H2

Air reactor

Me

Steam reactor

H2O

MeOx-1

Air

Figure 1. A simplified schematic of an ideal CLH system.8, 9 A key element in the CLH process is a high-performance oxygen carrier that can maintain a high hydrogen yield and good stability.13-15 Currently, utilization of the oxides of several transition metals (e.g. Ni, Fe, Cu, Mn, Co) has been investigated intensively.15 Among the various metal oxides, Fe-based oxygen carriers have the advantages of high oxygen carrying capacity, high melting temperature, low carbon deposition and environmental harmlessness, while a poor reactivity is the main deficiency.7, 16, 17 Ni-based oxides exhibit high reactivity, but carbon deposition, sintering and toxicity problems seriously impede their application.14 Nonetheless, it has been reported that a combination of these two types of oxygen carriers may offer positive synergy effects taking advantages of the favorable characteristics of each of them.18 Several researchers


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discovered that NiFe2O4 spinel phase formed from NiO-Fe2O3 composites at high temperatures exhibited higher oxygen-transfer capacity than individual NiO or Fe2O3.17, 19 Evdou et al.1 reported that NiFe2O4 synthesized by the solid-state method showed a high reactivity towards CH4. Kuo et al.9 found that NiFe2O4 particles produced via the solid-state method had better redox cycling performance and higher stability than the standard NiO and Fe2O3 particles in a chemical looping process. These results demonstrate that NiFe2O4 spinel is a potential candidate as oxygen carrier in chemical looping processes.1, 9 Furthermore, its ferromagnetic property can facilitate downstream separation from the solid-fuel ash.1 Generally speaking, NiFe2O4 is a kind of inverse cubic spinel presented as (Ni2+1-δFe3+δ)Td(Ni2+δFe3+2-δ)OhO2-4, where Td denotes the tetrahedral site and Oh refers to the octahedral site, as illustrated in Figure 2.20, 21

Figure 2. The NiFe2O4 spinel structure graphing.20, 21


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Although the NiFe2O4 spinel has already been studied in chemical looping processes as oxygen carrier1, 9, 17, 19, the impact of different synthesis methods on its performance has not been compared for the CLH process. Several researchers have observed that different synthesis methods can influence the size and morphology of NiFe2O4 nanoparticles.22, 23 Therefore, this paper aims to perform a systematic study to screen the optimal method for preparing NiFe2O4 spinel used in the CLH process and preliminarily investigate the cyclic performance of the screened oxygen carrier. The solid state, co-precipitation, hydrothermal and sol-gel methods were applied to prepare NiFe2O4 nanoparticles due to their simplicity and low cost compared to other methods like pulsed wire discharge, shockwave, reverse micelle co-precipitation, freeze drying, spray drying, ultrasonically assisted hydrothermal methods.22, 24-28 The prepared samples were characterized by means of XRD, Raman, SEM, XPS, BET and BJH respectively. Then the reduction reactivity and the ability of producing hydrogen of the synthesized samples were tested by thermogravimetric analysis. The redox test was performed in a lab-scale fixed-bed reactor for evaluating the hydrogen production capability and cyclic performance. Additionally, XRD, XPS and SEM analyses were also used to examine the post-reaction products.


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2 EXPERIMENTAL 2.1 Synthesis of NiFe2O4 spinel Nickel ferrite materials were prepared by the solid state (SS), co-precipitation (CP), hydrothermal (HT) and sol-gel (SG) methods. All the chemicals used in the work were analytical reagents. All the preparation conditions have been optimized on the basis of other papers.1, 9, 22, 29, 30 In the SS method, the required amounts of NiO and Fe2O3 powders were mixed in ethanol in a planetary ball mill (XQM-2L, Nanjing) at a rotation speed of 300rpm for 3 hours. For the other three methods, nickel nitrate hexahydrate [Ni(NO3)2·6H2O] and iron nitrate nonahydrate [Fe(NO3)3·9H2O] were used as raw materials and dissolved in deionized water, forming 1M of Ni(NO3)2 solution and 2M of Fe(NO3)3 solution, respectively. Ammonia was chosen to adjust pH in these three methods since sodium hydroxide may lead to the formation of sodium carbonate that will plug the pores and reduce the surface area.31, 32 In the CP method, ammonia was added into the mixed solution as a precipitating agent to make the pH reach 10. The suspension liquid was stirred and heated in water bath at 65 ºC for 1 hour. Afterwards the filtered precipitate through Buchner funnel was washed several times using deionized water. For the HT preparation, the pH value of the mixed solution was firstly adjusted to 7.5, and then the suspension was transferred into an autoclave, reacting at 160 ºC for 16 hours. After that the precipitate was washed several times by deionized water. In the SG synthesis, citric


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acid that is one of the common conventional chelating agent used in the sol-gel method 22 with the equivalent molar Ni(NO3)2 was added into the original mixed solution. Subsequently ammonia hydroxide was added to obtain a pH of 7.5. Finally the solution was heated at 65-75 ºC to evaporate 2/3 of the water, and the gel formed when the solution was cooled to room temperature. All the precursors obtained from the four methods were dried in a vacuum evaporator at 120 ºC and calcined for the formation of the ferrite phase in a muffle furnace under air atmosphere according to the same temperature program. In the first, the dried materials were calcined by increasing the temperature from 25 ºC to 400 ºC with a ramp of 8 ºC/min and keeping at 400 ºC for 2 hours. Then the sample was increased to 1200 ºC at a heating rate of 4 ºC/min, and kept at 1200 ºC for 2 hours. The selection of the temperature program is based on the knowledge that the precursor starts to convert into crystalline spinel structure at 400 ºC and the crystallization degree of NiFe2O4 spinel increases with the increasing calcination temperature.23, 33 2.2 Sample characterization The XRD analysis was carried out using equipment (X’Pert-PRO MPD) with Cu Kα radiation (λ = 1.54060 Å) at conditions of 40 kV and 40 mA at room temperature. The diffraction angles of 5-80°were scanned in every 0.0167°with a time interval of every 10 s. The Raman spectra of synthesized NiFe2O4 samples were collected at room temperature using the excitation line of 532 nm (Lab RAM HR800, HORIBA JY). The


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SEM images were obtained using a series of instruments (S-4800 FESEM, E-1010, HORIBA EX-250) at room temperature with the energy diffusivity of less than 0.2 eV, displaying the surface topography of samples. For porosity analysis of the fresh and post-reaction samples, N2 adsorption–desorption (Quantachrome, SI-MP-10) was conducted after degassing at 280ºC for 21.25 hours. The specific surface area (SBET) was then calculated according to the Brunauer-Emmett-Teller (BET) method based on the adsorption isotherm, while pore diameter and pore volume were derived from the desorption isotherm by means of Barrett–Joyner–Halenda (BJH). An XPS analyzer was used to probe the surface composition of the fresh and the reacted samples in the equipment (ESCALAB 250Xi, Thermo Fisher Scientific Inc.) with an Al Kα X-ray source (10 mA, 20 kV), under the conditions of 20 eV and 100 eV pass energy for the survey spectra and the single element spectra (Ni, Fe, O, C), respectively. 2.3 TGA test The reducibility of the prepared samples was investigated in a TGA reactor (Linseis, PT/2 1600), by exposing oxygen carrier to 10% CO (balance argon). 200 mg of the prepared nickel ferrite particles placed in an alumina crucible were heated to 1000 ºC at a heating rate of 10 ºC/min and maintained at 1000 ºC for 55 min under a reducing gas flowrate of 0.60 L/min, followed by only purging gas (argon) flowing at 1000 ºC for 30 min in order to remove CO in the system. Then for testing the ability of producing


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hydrogen, oxidation of the reduced sample was performed under 7% steam (balance argon) at a total flow rate of 0.98 L/min at 1000 ºC for 60 min, and then changed to pure argon atmosphere in the cooling process. To study the reduction and recovery degree of NiFe2O4,

Plose, theo

and

Pre cov ery , theo

were

calculated using the following Eqs.(1)-(2) assumed to be pure NiFe2O4, and the recovery degree of lattice oxygen

Plose, theo (%)  where

M [O] M NiFe2O4

Plose, theo

Ract was defined as Eq.(3):

100%

(1)

means the theoretical final weight loss percentage assumed that all the

lattice oxygen ([O]) of NiFe2O4 was consumed in the end, %; lattice oxygen in 1 mol of NiFe2O4 , g;

 M Ni  Fe2  Pre cov ery , theo (%)  1   M Ni  Fe2O8 3 

where

Pre cov ery , theo

M NiFe2O4

M [O]

means the mass of

means the mass of 1 mol of NiFe2O4, g.

   100%  

(2)

means the theoretical weight recovery percentage from the Ni-Fe state

to the Ni-Fe3O4 state in the steam oxidation of the TGA test, %; of 1 mol of the fully reduced nickel ferrite, g;

M Ni  Fe2O8 3

M Ni  Fe2

means the mass

means the mass of 1 mol of

reoxidized nickel ferrite by steam, g.

Ract  where

Pre cov ery , act Pre cov ery , theo

Ract

100%

(3)

means the recovery degree of lattice oxygen in the steam oxidation of the

TGA test, %;

Pre cov ery , theo

means the theoretical weight recovery percentage calculated by


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Eq. (2), %;

Pre cov ery , act

means the actual weight recovery percentage obtained from the

TGA test, %. 2.4 Fixed-bed test The prepared NiFe2O4 samples and Fe2O3 (for comparison) were further evaluated in a lab-scale fixed-bed reactor for their hydrogen production capability and cyclic performance. The experimental setup is shown in Figure 3. Prior to each test, 500 mg of sample was loaded at a distance of 420 mm from the bottom of a quartz reactor which had an inner diameter of 15 mm, an outer diameter of 20 mm and a length of 800 mm. A K-type thermocouple with a diameter of 3 mm was used to measure the temperature at the point of 15 mm below the carrier. The reactor was initially heated to a temperature of 850 ºC by a heating furnace under a N2 flowrate of 50 mL/min. Then the gas atmosphere was changed to a mixture of 24% H2, 24% CO, 12% CO2 and 40% N2, which simulates biomass pyrolysis gas used to reduce the sample. Afterwards water droplets were injected at the top of the reactor at the speed of 0.2 mL/min, which evaporated rapidly and carried by a N2 flowrate of 50 mL/min through the system to make the gas atmosphere consisting of 33% H2O and 67% N2. Finally the carrier was oxidized by an air flowrate of 100 mL/min. Nitrogen purging was introduced for 15 min during the shift from one step to the next. The flue gas was collected by gas bags and analyzed by a gas chromatograph (GC-2010 Plus, SHIMADZU). Table 1 shows the detail experimental operations in a single redox test and in one redox of a cyclic test, respectively. Furthermore, the


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hydrogen yield was calculated by the nitrogen-balanced principle, and hydrogen production capability was evaluated by  (mL/g), which means the volume of hydrogen produced in one redox for 1 g of lattice oxygen [O] in oxygen carrier.



Vtotal m  [O ]

Where

(4)

Vtotal means the total hydrogen yield in each redox reaction, mL; m means the

weight of the original sample (0.5g), g;

[O ]

means the mass percentage of lattice

oxygen of oxygen carrier (for NiFe2O4, 27.3%; for Fe2O3, 30%), %.

Flow pump

H2O Mass flow controllers Furnance Oxygen carrier

Fine quartz wool

Temperature controllers

Cooler Dryer


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Figure 3. Schematic diagram of the fixed-bed setup.


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Table 1. The operations in the fix-bed tests A single redox test The reduction step: 35 min, the flue gas collected by 3.5 min/bag; The steam oxidization step: 60 min, the flue gas collected by 3 min/bag in the first 30 min and 6 min/bag in the second 30 min; The air oxidization step: 15 min. Each redox of a cyclic test The reduction step: 35 min, the flue gas collected in one bag; The steam oxidization step: 40 min, the flue gas collected in one bag; The air oxidization step: 15 min.

3 Results and Discussions 3.1 XRD and Raman analysis of as-synthesized oxides According to the reference pattern (JCPDS PDF 00-010-0325) of NiFe2O4 spinel, typical reflections should exhibit at 2θ≈18.4 (111), 30.3 (220), 35.7 (311), 37.3 (222), 43.4 (400), 53.8 (422), 57.4 (511), 62.9 (440), 71.5 (620), 74.6 (533), 75.6 (622) from the corresponding planes labeled in brackets that present cubic spinel structure. As shown in Figure 4, all the synthesized samples exhibit pure NiFe2O4. In the Raman spectra of Figure 5, the characteristic bands of the prepared samples were located approximately at 210 cm-1, 334 cm-1, 488 cm-1, 574 cm-1, 702 cm-1, which fitted well with those of the


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commercial NiFe2O4 (Aladdin). Therefore, it is confirmed that all the synthesized

0 9000 6000

(620) (622)

(511)

(440)

(422)

(533)

3000

(400)

6000

(222)

SG (111)

9000

(220)

(311)

products are pure NiFe2O4 spinels.

Intensity (a.u.)

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SS

3000 0 9000 6000

HT

3000 0 9000 6000

CP

3000 0

10

20

30

40

50

60

70

80

degree

Figure 4. XRD patterns of the prepared NiFe2O4 samples.


(488) (574)

(334)

(210)

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(702)

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Commercial SG SS HT CP 100

200

300

400

500

600

700

800

900

-1

Wavenumber (cm )

Figure 5. Raman spectra of the prepared NiFe2O4 samples and the commercial product. 3.2 Surface area and porosity analysis of as-synthesized oxides The particle size and the surface area may highly influence the dispersion of active sites and the accessibility of reactants to active sites.34, 35 In general, a larger surface area, a larger pore volume and a smaller pore diameter lead to more active sites and consequently a higher reactivity. The results of specific surface area and porosity of the synthesized NiFe2O4 materials are listed in Table 2. Because of calcination at a high temperature (1200 ºC), these samples have relatively small surface area and low pore volume. BET specific surface area and BJH pore volume of the SG sample are much larger than the other samples, subsequently followed by the SS sample, the CP sample and the HT sample. The HT sample has a slightly larger SBET than the CP sample, while the CP material has a little larger BJH pore volume than the HT material. Overall, the


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surface area and porosity of these two samples are very close. Furthermore, the SG and SS materials have similar BJH pore diameters, and the BJH pore diameters of the CP and HT samples are similar. Table 2. Surface area and porosity analysis of the prepared samples SBET

BJH pore diameter

BJH pore volume

(m2/g)

(nm)

(cc/g)

SG

4.891

3.060

0.011

SS

2.365

3.068

0.004

HT

1.902

3.340

0.002

CP

1.116

3.384

0.003

Samples

3.3 XPS surface chemical analysis of as-synthesized oxides The XPS measurements were performed to determine the surface composition of the synthesized NiFe2O4 materials (Table 3). The binding energies of Ni 2p3/2 and Fe 2p3/2 in NiFe2O4 were found to be at the ranges of 854.9-855.4 eV and 709−711 eV in the literatures.29, 36 It can be seen that Ni 2p3/2 photopeaks of all the samples located in that scale (855.09 eV for SG, 855.35 eV for SS, 855.11 eV for HT, 854.98 eV for CP). It can also be observed that the binding energy of Fe 2p3/2 for each sample is within that range (710.91 eV for SG, 711.15 eV for SS, 710.85 eV for HT, 710.57 eV for CP). Moreover, the surface atomic ratio of Fe to Ni was calculated for the four samples. The results in


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Table 3 shows that the Fe/Ni ratios of each sample fluctuate around 2 (the theoretical value), which means there exists an excess of iron or nickel on the surface of prepared samples. Table 3. XPS data of the fresh NiFe2O4 samples and steam-oxidized products The fresh NiFe2O4 samples

The steam-oxidized products

Samples

Fea

Nia

Fe/Nib

Products

Fea

Nia

Fe/Nib

SG

710.91

855.09

2.30

SG-CO-H2O

710.22

854.80

2.93

SS

711.15

855.35

2.11

SS-CO-H2O

709.57

HT

710.85

855.11

1.58

HT-CO-H2O

710.06

CP

710.57

854.98

1.83

CP-CO-H2O

710.07

a

Binding energy (eV); b Theoretical atomic ratio Fe/Ni = 2.

3.4 Morphological analysis of as-synthesized oxides Figure 6 shows the morphology of the synthesized NiFe2O4 particles by SEM analysis. For each sample, the location of the higher magnification image (right) was marked in the corresponding lower magnification image (left). Obviously, none of the four materials are individual crystals, as consistent with their XRD patterns in which there are several typical reflections of crystal planes presenting different spinel structures. Therefore, the SEM images reveal heterogeneous crystal systems and the presence of grains growth and aggregation in different extents ascribed to calcination at high temperatures. SEM images of SG show aggregates of particles of 0.12 to 0.2 μm, which have definite boundaries and


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the grain-to-grain connectivity with air holes. The SS material shows platelike crystal morphology, some parts having a crystalline aspect. The surface of the HT spinel is relatively smooth on which several small granules inlay. The CP surface seems glassy-like with aggregates of particles of uneven sizes. Generally, the SG sample appear to be more porous and in much smaller particle sizes than the others, which is assumed that the combustion of organic material (citric acid) initially during the calcination process may be beneficial for the porous structure of the SG sample. In many literatures, the sol-gel method was also regarded to be a feasible and attractive technique to obtain the particles with high phase purity, chemically homogeneous and a narrow size distribution.37,38


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(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)


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Figure 6. SEM images of the prepared NiFe2O4 samples at different magnifications: (a) and (b) SG, (c) and (d) SS, (e) and (f) HT, (g) and (h) CP. 3.5 Reactivity test in TGA The reduction behavior of the samples under CO was inspected by thermogravimetric analysis. The TG and DTG curves are shown in Figure7. The final weight loss of four samples (SG, SS, HT and CP) were 26.85%, 26.75%, 26.53%, and 27.30%, respectively, which were close to the theoretical value (27.30%) calculated by Eq.(1), indicating a complete reduction for all the metal oxides. Additionally, it is also an evidence of full reduction that the TG curves went stable in the end. There are several peaks in the DTG curve of each sample. The first peaks of the SG and SS samples appear a little earlier than those of the HT and CP materials, and the initial weight loss rate of the samples are in the order of SG>SS>CP>HT. The reduction of NiFe2O4 took place as a stepwise process as shown by the multi peak DTG curves for each sample. Generally the pathway is suggested: NiFe2O4→Ni-Fe2O3→Ni-Fe3O4→ Ni-FeO→Ni-Fe, as summarized in Eqs.(5)-(9).29 Initially at low temperatures (500-600 ºC), Ni2+ is reduced to Ni0 as Eq.(5), and then Fe3O4 is generated due to that part of Fe3+ is reduced to Fe2+ via Eq.(6) and Eq.(7). Afterwards the increasing temperatures favor the endothermic reaction as Eq.(8) which usually occurs at high temperatures, and following to form Fe0 via Eq.(9).

NiFe2O4  Ni  Fe2O3  O

(5)

Fe2O3  2FeO  O

(6)

Fe2O3  FeO  Fe3O4

H  18.05 kJ mol T  973.15K 

(7)

Fe3O4  3FeO  O

H  295.88 kJ mol T  973.15K 

(8)

FeO  Fe  O

(9)


Energy & Fuels

a) 1200

95

1000

TG (%)

100

SG SS HT CP

90 85

800 600

80

400

75

200

70

Temperature (C)

0 0

20

40

60

80

100

120

140

Time (min)

b) 1200

0.0

1000

DTG (%/min)

-0.2 800 -0.4

600

SG SS HT CP

-0.6

-0.8

400

Temperature (C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 42

200 0

0

20

40

60

80

100

120

140

Time (min)

Figure 7. TG and DTG curves for the CO reduction. The hydrogen production capability was investigated by placing the reduced NiFe2O4 samples under gas (7% H2O and 93% Ar) at 1000 ºC, which is also a process of lattice oxygen recovery. Figure 8 shows the TG and DTG curves of the steam oxidation, and the characteristic parameters of the TG analysis are listed in Table 4. Some papers have pointed out that the reduced nickel oxide or metallic nickel were difficult to oxidize by steam due to thermodynamic limitations.7, 9, 16 Most of the reduced nickel ferrite could


Page 23 of 42

only be oxidized to be a mixture of Fe3O4 and Ni under steam according to a reaction like Eq.(10).9 It has to be recovered to the initial state by air through Eq.(11).9 Thus the theoretical weight recovery percentage

Pre cov ery , theo

was calculated to be 25.1% according to

Eq.(2) assuming that the sample was oxidized by steam from the Ni-Fe state to the Ni-Fe3O4 state, while the practical ones were directly obtained from the test. None of the reduced samples recovered to the theoretical value, but they exhibited very different recovery degrees of lattice oxygen

Ract . The reduced SG sample gave the highest

recovery degree (86.8%) as well as the largest mass change rate (2.99 %/min), and the others lagged far behind. The results confirmed that the reduced nickel ferrite can partially recover lattice oxygen and produce hydrogen through the water-splitting process.

Ni  3Fe  4H 2O  Ni  Fe3O4  4H 2

(10)

2 4 Ni  Fe3O4  O2 g   air   NiO  Fe2O3  NiFe2O4 3 3

(11)

a)

25

20

TG (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

15

10

SG SS HT CP

5

0 0

10

20

30

40

50

60

Time (min)


Energy & Fuels

b) 3.0

SG SS HT CP

2.4

DTG (%/min)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 42

1.8 1.2 0.6 0.0

0

10

20

30

40

50

60

Time (min)

Figure 8. TG and DTG curves for the steam oxidation.

Table 4. The characteristic parameters of TG analysis in the steam oxidation

Reduced sample

Maximal weight

Final weight

The recovery

recovery rate

recovery

degree of lattice

(%/min)

a

Pre cov ery , act

(%)

oxygen Ract a (%)

SG

2.99

21.78

86.77

SS

1.13

11.93

47.53

HT

1.88

14.42

57.45

CP

1.19

11.66

46.45

Theoretical recovery degree of lattice oxygen

Ract

equals to 1.

Textural and surface properties of the fresh NiFe2O4 materials and steam-oxidized products were compared by XPS and SEM analyses, shown in Table 3 and Figure 9. The results of XPS analysis indicate that Ni content cannot be detected on the surfaces of the SS, CP and HT products, while the surface atomic Fe/Ni ratio of the SG product increases slightly from 2.30 to 2.93, meaning a slight agglomeration of Ni particles. It has been


Page 25 of 42

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Energy & Fuels

found that in the steam oxidation process, an outer layer of Fe3O4 forms quickly in a short time coexisting with the Ni-enriched alloy phase, but after a very long period Ni starts to merge into the spinel layer.6,39 It means that the spinel structure cannot be fully recovered in the limited time and most of nickel particles won’t be exposed on the surface of the steam-oxidized products, which can put evidence in no detection of external Ni particles for the SS-H2O, CP-H2O and HT-H2O products by XPS. And enough stability and dispersion degree of Ni may be the main reason for its presence on the SG-H2O surface. Figure 9 shows that particles grew to blocks and pore structures disappeared from surface after the CO-H2O redox, which describes the morphology of the prepared samples and the steam-oxidized products by SEM at the same magnification. But the SG product appears to be lighter agglomeration and the existence of several pore structures. Furthermore, a considerable loss of surface area may also be caused by high surface tension of water molecule closing small mesopores.40-42


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 42

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)


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Energy & Fuels

Figure 9. SEM images of the prepared samples and steam-oxidized products: (a) fresh SG, (b) SG-H2O, (c) fresh SS, (d) SS-H2O, (e) fresh HT, (f) HT-H2O, (g) fresh CP, (h) CP-H2O. 3.6 Redox test in fixed-bed reactor Figure 10 plots the evolution of gas concentration and hydrogen yield with respect to time of the SG and Fe2O3 samples for one single redox in the fixed-bed experiment. In the reduction step, the curves of Fe2O3 went flat much earlier than those of SG, with complete reduction to metallic iron occurring in the first 10 min approximately. And the H2 and CO levels of SG are lower compared to Fe2O3 while its concentration of CO2 is much higher during the reaction process, meaning more depletion of reducing gases (H2 and CO) and better oxygen capacity of NiFe2O4. For the subsequent process, steam-oxidation of the Fe-based sample was rapider than the reduced NiFe2O4, though the hydrogen yields of both reached their maximum values in a very short time, indicating instantly decomposing steam to produce H2. It can be seen that after the top level, the concentration of hydrogen fell sharply in case of Fe2O3, while H2 level of SG slowly returned to baseline. Although initially the H2 concentration of Fe2O3 is higher than that of SG, the total amount of produced hydrogen in case of SG is much greater compared to Fe2O3, shown in Figure 11. Figure 11 also compares the hydrogen production capability of four samples in the fixed-bed experiments. Obviously, the SG sample shows the highest hydrogen yield.


Energy & Fuels

a1)

25

SG Fe2O3

H2 Concentration (%)

20

15

10

5

0 0

5

10

15

20

25

30

35

25

30

35

Time (min)

a2) SG Fe2O3

30

CO Concentration (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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25 20 15 10 5 0 0

5

10

15

20

Time (min)


Page 29 of 42

a3) SG Fe2O3

CO2 Concentration (%)

40

30

20

10

0 0

5

10

15

20

25

30

35

Time (min)

b)

Hydrogen yield (ml/min)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

24

SG Fe2O3

20

16

12

8

4

0 0

10

20

30

40

50

60

Time (min)

Figure 10. Gas concentration and hydrogen yield of the SG sample along with the reaction time at 850 ºC in fixed-bed reactor ((a1)-(a3) gases concentrations of the SG and Fe2O3 samples for the reduction step; (b) hydrogen yield of the SG and Fe2O3 samples for the steam oxidation step).


Energy & Fuels

1800 1600 1400

mL/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1200 1000 800 600 400 200 0

SG

SS

HT

CP

Fe2O3

Figure 11. Hydrogen production capability of the NiFe2O4 and Fe2O3 samples during redox reaction.

Figure 12 shows the XRD spectrogram of the four oxidized samples after the same redox process. It can be seen that most characteristic peaks of NiFe2O4 (pointed by “A”) were detected in the XRD patterns in Figure12, but several typical reflections of Fe2O3 (marked by circles) also appeared. It is known that the lines of Fe2O3 (JCPDS PDF 01-084-0306) and Fe3O4 (JCPDS PDF 01-075-0449) may overlap with those of NiFe2O4. It is guessed that most of NiFe2O4 spinel retained its structure, but some did not because of sintering. Furthermore, it can be seen that these four products performed different intense peaks. The intensity of the SG product for XRD peaks was recorded to be much greater than that of the others, implying better growth of the particle size and higher degree of crystallization.23 Therefore, among the four samples, the SG sample is considered to be the best candidate for the cyclic test. In fact, NiFe2O4 spinel can be regarded as a way to decrease the size of Ni particles which is an oxygen carrier of high activity but also a vital element of deactivation because of sintering.43,30,29 Thus nanoparticles of nickel can be dispersed on or stabilized


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Page 31 of 42

by the oxidic matrix resulting in a dilution effect of nickel active sites on which carbon deposition more easily occur like Eq.(12).29 If a stable nickel metallic species is obtained through delivering active Ni0 particles in the reduction stage, the reactivity of reduced nickel ferrites is assumed to be relatively high with steam to produce hydrogen due to the relieved sintering problem. According to the results from XPS analysis (Table 3), the order of Fe/Ni ratios is SG>SS>HT>CP, as is in good agreement with the hydrogen production capability of the four samples. Furthermore, a kind of Ni-Fe synergistic effect is assumed since the reduced NiFe2O4 has a stronger capability of hydrogen production than Fe2O3, although most of nickel particles cannot be oxidized and return to spinel structure through the steam oxidation. And the effect is thought to be strongest in the NiFe2O4 spinel prepared by the sol-gel method according to the experimental result. (12)

2CO  C  CO2 10000 7500

A

A---NiFe2O4

SG

5000

A

2500

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

A

A

A

A

A AAA

A

0 5000

A

SS

2500

A

A

A

A

A

AA

A

A

A A

A

A

A

A

A

0 2500

HT

A

A

0 5000

A

CP

2500

A

A

A

AAA

0 10

20

30

40

50

60

70

80

degree

Figure 12. XRD patterns of the oxidized NiFe2O4 products. 3.7 Cyclic test in fixed-bed reactor The results of the redox test in TGA and fixed-bed reactors show that the SG sample has the best performance with respect to hydrogen yield. Thus twenty redox cycles were


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

performed to test the cyclic performance of the individual SG sample and the SG sample mixed with SiO2 powders in equal weight at 850 ºC. The hydrogen production capability in the steam oxidation step of each cycle is shown in Figure 13. It can be seen that a slump in the hydrogen yield occurred with the cycles proceeding for the individual SG sample, which may be ascribed to the agglomeration problem caused by the presence of Ni. Therefore, SiO2 powder was used as the inert component to mechanically mix with the SG sample for a better dispersion of nickel ferrite species to avoid or at least alleviate the sintering problem. Figure 13(b) shows that hydrogen production capability can remain stable after the second cycle for the mixed sample. Furthermore, it can be seen that several typical peaks of NiFe2O4 and SiO2 existed in the XRD patterns of the fresh and post-reaction of mixture of NiFe2O4 and SiO2, and some of them may overlap, marked by “A” and “B” (Figure 14). The intensity of all the peaks in the post-reaction product was observed to be lower than that in the fresh mixture, which can be ascribed to sintering. The morphology of the fresh samples and cycling products was compared by SEM analysis in Figure 15. It can be seen that both materials became larger in size and rougher on surface after 20 cycles. Nevertheless, the mixed cycling product presents a wider distribution of aggregates size and more unsmooth surfaces with many grains dispersing on.


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a) 1200

mL/g)

1000 800 600 400 200 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Cycle number

b)

1200 1000

mL/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

800 600 400 200 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Cycle number

Figure 13. Hydrogen production capability on the basis of the number cycles at 850 ºC in the fixed-bed reactor ((a) individual SG sample; (b) for the SG sample mixed with SiO2 powders in equal weight).


Energy & Fuels

10000

A---NiFe2O4

A(B)

Fresh

B---SiO2

B

7500

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

5000

A(B)

A A

2500

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A(B)

A

BB B

A

A A A

B B

A

BB

A(B)

0

A(B)

Post-reaction B

5000

A

2500

0

10

20

BB

A B

30

A(B)

A A

40

50

60

A

70

80

degree

Figure 14. XRD patterns of the fresh and post-reaction mixture of NiFe2O4 and SiO2.

(a)

(b)

(c)

(d)


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Energy & Fuels

Figure 15. SEM images of the prepared samples and the cycling products: (a) fresh SG, (b) cycling SG, (c) fresh mixture of SG and SiO2, (d) cycling mixture of SG and SiO2.

It is to be noted that a simple mechanical mixture of NiFe2O4 and SiO2 cannot be applied in the real fluidized bed for the chemical looping process. Moreover, many materials like Al2O3, NiAl2O4, TiO2, and ZrO2 as the binder with NiO particles have been studied and tested in fluidized beds for solving the agglomeration problem.44-46 Consequently the reactivity of the NiFe2O4-based supported on different inert materials needs to be investigated in the further work. 4 Conclusion In the present work, nanoparticles of NiFe2O4 were prepared by the solid state, co-precipitation, hydrothermal and sol-gel methods, and characterized with a series of analytical tools. All the samples appear to have the ability to provide their lattice oxygen to the fuel, then react with steam to produce H2 and finally almost recover to the original state in the presence of air. The material prepared by the sol-gel method showed the best hydrogen production capability in the TGA and fixed-bed tests. On the basis of the characterization of the particles, it is believed that the reactivity of the four samples was affected by a combination of surface area, porosity and surface chemical composition. Moreover, in the cyclic test, the SG sample deactivated very fast due to sintering, whereas the mixture of NiFe2O4 and SiO2 showed desirable resistance to deactivation during 20 redox cycles at 850 ºC during the CLH process.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

AUTHOR INFORMATION Corresponding Author *Fang He Telephone: + 86-02087057721 Fax: +86-02087057737 Email: [email protected]. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT

The authors gratefully acknowledge the financial support by the National Natural Science Foundation of China (51406214, 51406208). This work was also supported by the Natural Science Foundation of Guangdong Province (2015A030313719) and the Science & Technology Research Project of Guangdong Province (2013B050800008, 2015A010106009).

ABBREVIATIONS CLH

Chemical looping hydrogen production

SS

Solid state


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Energy & Fuels

CP

Co-precipitation

HT

Hydrothermal

SG

Sol-gel

XRD

X-ray diffraction

SEM

Scanning electron microscopy

XPS

X-ray photoelectron spectroscopy

BET

Brunauer-Emmett-Teller

BJH

Barrett-Joyner-Halenda

MeOx

Metal oxide

Me

Reduced oxygen carrier

MeOx-1

Partially oxidized oxygen carrier

BV

Binding energy


Energy & Fuels

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References

1. Evdou, A.; Zaspalis, V.; Nalbandian, L. Ferrites as redox catalysts for chemical looping processes. Fuel 2016, 165, 367-378. 2. Udomsirichakorn, J.; Salam, P. A. Review of hydrogen-enriched gas production from steam gasification of biomass: The prospect of CaO-based chemical looping gasification. Renew. Sust. Energ. Rev. 2014, 30, 565-579. 3. Hossain, M. M.; de Lasa, H. I. Chemical-looping combustion (CLC) for inherent CO2 separations-a review. Chem. Eng. Sci. 2008, 63 (18), 4433-4451. 4. Go, K.; Son, S.; Kim, S.; Kang, K.; Park, C. Hydrogen production from two-step steam methane reforming in a fluidized bed reactor. Int. J. Hydrogen Energy 2009, 34 (3), 1301-1309. 5. Solunke R.; Veser G. Hydrogen Production via Chemical Looping Steam Reforming in a Periodically Operated Fixed-Bed Reactor. Ind. Eng. Chem. Res. 2010, 49 (21), 11037–11044. 6. Aston, V. J.; Evanko, B. W.; Weimer, A. W. Investigation of novel mixed metal ferrites for pure H2 and CO2 production using chemical looping. Int. J. Hydrogen Energy 2013, 38 (22), 9085-9096. 7. Gupta, P.; Velazquez-Vargas, L. G.; Fan, L. S. Syngas redox (SGR) process to produce hydrogen from coal derived syngas. Energy Fuels 2007, 21 (5), 2900-2908. 8. Puig-Arnavat, M.; Bruno, J. C.; Coronas, A. Review and analysis of biomass gasification models. Renew. Sust. Energ. Rev. 2010, 14 (9), 2841-2851. 9. Kuo, Y.-L.; Hsu, W.-M.; Chiu, P.-C.; Tseng, Y.-H.; Ku, Y. Assessment of redox behavior of nickel ferrite as oxygen carriers for chemical looping process. Ceram. Int. 2013, 39 (5), 5459-5465. 10. Zhang, X.; Jin, H. Thermodynamic analysis of chemical-looping hydrogen generation. Appl. Energy 2013, 112, 800-807.


Page 38 of 42

Page 39 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

11. Scheffe, J. R.; Li, J.; Weimer, A. W. A spinel ferrite/hercynite water-splitting redox cycle. Int. J. Hydrogen Energy 2010, 35 (8), 3333-3340. 12. Huang, Z.; He, F.; Feng, Y.; Liu, R.; Zhao, K.; Zheng, A.; Chang, S.; Zhao, Z.; Li, H. Characteristics of biomass gasification using chemical looping with iron ore as an oxygen carrier. Int. J. Hydrogen Energy 2013, 38 (34), 14568-14575. 13. Sun, S.; Zhao, M.; Cai, L.; Zhang, S.; Zeng, D.; Xiao, R. Performance of CeO2-Modified Iron-Based Oxygen Carrier in the Chemical Looping Hydrogen Generation Process. Energy Fuels 2015, 29 (11), 7612-7621. 14. Adanez, J.; Abad, A.; Garcia-Labiano, F.; Gayan, P.; de Diego, L. F. Progress in Chemical-Looping Combustion and Reforming technologies. Prog. Energ. Combust. 2012, 38 (2), 215-282. 15. Fan, L. S.; Zeng, L.; Luo, S. W. Chemical-Looping Technology Platform. Aiche J. 2015, 61 (1), 2-22. 16. Li, F. X.; Kim, H. R.; Sridhar, D.; Wang, F.; Zeng, L.; Chen, J.; Fan, L. S. Syngas Chemical Looping Gasification Process: Oxygen Carrier Particle Selection and Performance. Energy Fuels 2009, 23 (8), 4182-4189. 17. Huang, Z.; He, F.; Feng, Y.; Zhao, K.; Zheng, A.; Chang, S.; Wei, G.; Zhao, Z.; Li, H. Biomass Char Direct Chemical Looping Gasification Using NiO-Modified Iron Ore as an Oxygen Carrier. Energy Fuels 2014, 28 (1), 183-191. 18. Pena, J. A.; Lorente, E.; Romero, E.; Herguido, J. Kinetic study of the redox process for storing hydrogen reduction stage. Catal. Today 2006, 116 (3), 439-444. 19. Yang, S.; Kim, K.; Baek, J. I.; Kim, J. W.; Lee, J. B.; Ryu, C. K.; Lee, G. Spinel Ni(Al,Fe)2O4 Solid Solution as an Oxygen Carrier for Chemical Looping Combustion. Energy Fuels 2012, 26 (7), 4617-4622. 20. Goldman, A. Modern Ferrite Technology. Springer US: New York, 2005, P 438. 21. Wells A. F.; O'Brien T. D. Structural Inorganic Chemistry. J. Phys. Chem. 1946, 50 (5), 443–443.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

22. Srivastava, M.; Chaubey, S.; Ojha, A. K. Investigation on size dependent structural and magnetic behavior of nickel ferrite nanoparticles prepared by sol–gel and hydrothermal methods. Mater. Chem. Phys. 2009, 118 (1), 174-180. 23. Din, I. U.; Tasleem, S.; Naeem, A.; Shaharun, M. S.; Nasir, Q. Study of Annealing Conditions on Particle Size of Nickel Ferrite Nanoparticles Synthesized by Wet Chemical Route. Synthe. React. Inorg. M. 2015, 46 (3), 405-408. 24. Kinemuchi, Y.; Ishizaka, K.; Suematsu, H.; Jiang, W. H.; Yatsui, K. Magnetic properties of nanosize NiFe2O4 particles synthesized by pulsed wire discharge. Thin Solid Films 2002, 407 (1-2), 109-113. 25. Zhou, J.; Ma, J. F.; Sun, C.; Xie, L. J.; Zhao, Z. Q.; Tian, H.; Wang, Y. G.; Tao, J. T.; Zhu, X. Y. Low-temperature synthesis of NiFe2O4 by a hydrothermal method. J. Am. Ceram. Soc. 2005, 88 (12), 3535-3537. 26. Morrish, A. H.; Haneda, K. Magnetic-structure of small NiFe2O4 particles. J. Appl. Phys. 1981, 52 (3), 2496-2498. 27. Komarneni, S.; Fregeau, E.; Breval, E.; Roy, R. Hydrothermal preparation of ultrafine ferrites and their sintering. J. Am. Ceram. Soc. 1988, 71 (1), C26-C28. 28. Liu, J. J.; He, H. L.; Jin, X. G.; Hao, Z. P.; Hu, Z. Q. Synthesis of nanosized nickel ferrites by shock waves and their magnetic properties. Mater. Res. Bull. 2001, 36 (13-14), 2357-2363. 29. Benrabaa, R.; Boukhlouf, H.; Löfberg, A.; Rubbens, A.; Vannier, R.-N.; Bordes-Richard, E.; Barama, A., Nickel ferrite spinel as catalyst precursor in the dry reforming of methane: Synthesis, characterization and catalytic properties. Journal of Natural Gas Chemistry 2012, 21 (5), 595-604. 30. Benrabaa, R.; Löfberg, A.; Rubbens, A.; Bordes-Richard, E.; Vannier, R. N.; Barama, A. Structure, reactivity and catalytic properties of nanoparticles of nickel ferrite in the dry reforming of methane. Catal. Today 2013, 203, 188-195. 31. Benrabaa, R.; Boukhlouf, H.; Bordes-Richard, E.; Vannier, R. N.; Barama, A.


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Nanosized nickel ferrite catalysts for CO2 reforming of methane at low temperature: effect of preparation method and acid-base properties. In Scientific Bases for the Preparation of Heterogeneous Catalysts: Proceedings of the 10th International Symposium 2010, 175, 301-304. 32. Benrabaa, R.; Boukhlouf, H.; Barama, S.; Bordes-Richard, E.; Vannier, R. N.; Barama, A. Structural, Textural and Acid-Base Properties of Nano-Sized NiFe2O4 Spinel Catalysts. Catal. Lett. 2012, 142 (1), 42-49. 33. Ceylan, A.; Ozcan, S.; Ni, C.; Ismat Shah, S. Solid state reaction synthesis of NiFe2O4 nanoparticles. J. Magn. Magn. Mater. 2008, 320 (6), 857-863. 34. Cavani, F.; Trifiro, F.; Vaccari, A. Hydrotalcite-type anionic clays: preparation, properties and applications. Catal. Today 1991, 11 (2), 173-301. 35. Sadykov, V. A.; Gubanova, E. L.; Sazonova, N. N.; Pokrovskaya, S. A.; Chumakova, N. A.; Mezentseva, N. V.; Bobin, A. S.; Gulyaev, R. V.; Ishchenko, A. V.; Krieger, T. A.; Mirodatos, C. Dry reforming of methane over Pt/PrCeZrO catalyst: Kinetic and mechanistic features by transient studies and their modeling. Catal. Today 2011, 171 (1), 140-149. 36. http://www.lasurface.com. 37. Li, D.-y.; Sun, Y.-k.; Gao, P.-z.; Zhang, X.-l.; Ge, H.-l. Structural and magnetic properties of nickel ferrite nanoparticles synthesized via a template-assisted sol–gel method. Ceram. Int. 2014, 40 (10), 16529-16534. 38. Chen D.-H.; He X.-R. Synthesis of nickel ferrite nanoparticles by sol-gel method. Mater. Res. Bull. 2001, 36, 1369–1377. 39. Menzies I, L. J. Oxidation of an Fe-12% Ni Alloy in Oxygen at 700 °C-1000 °C. Oxid. Met. 1971, 3, 41-58. 40. Kustrowski, P.; Sulkowska, D.; Chmielarz, L.; Dziembaj, R. Aldol condensation of citral and acetone over mesoporous catalysts obtained by thermal and chemical activation of magnesium-aluminum hydrotalcite-like precursors. Appl. Catal. A-Gen. 2006, 302 (2),


Energy & Fuels

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317-324. 41. Manova, E.; Tsoncheva, T.; Paneva, D.; Mitov, I.; Tenchev, K.; Petrov, L. Mechanochemically synthesized nano-dimensional iron-cobalt spinel oxides as catalysts for methanol decomposition. Appl. Catal. A-Gen. 2004, 277 (1-2), 119-127. 42. Varadwaj, K. S. K.; Panigrahi, M. K.; Ghose, J. Effect of capping and particle size on Raman laser-induced degradation of gamma-Fe2O3 nanoparticles. J. Solid State Chem. 2004, 177 (11), 4286-4292. 43. Benrabaa, R.; Löfberg, A.; Guerrero Caballero, J.; Bordes-Richard, E.; Rubbens, A.; Vannier, R.-N.; Boukhlouf, H.; Barama, A. Sol–gel synthesis and characterization of silica supported nickel ferrite catalysts for dry reforming of methane. Catal. Commun. 2015, 58 (5), 127-131. 44. Mattisson, T.; Johansson, M.; Lyngfelt, A. The use of NiO as an oxygen carrier in chemical-looping combustion. Fuel 2006, 85 (5-6), 736-747. 45. Gayan, P.; de Diego, L. F.; Garcia-Labiano, F.; Adanez, J.; Abad, A.; Dueso, C. Effect of support on reactivity and selectivity of Ni-based oxygen carriers for chemical-looping combustion. Fuel 2008, 87 (12), 2641-2650. 46. Cho, P.; Mattisson, T.; Lyngfelt, A. Defluidization conditions for a fluidized bed of iron oxide-, nickel oxide-, and manganese oxide-containing oxygen carriers for chemical-looping combustion. Ind. Eng. Chem. Res. 2006, 45, (3), 968-977.


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Screening of NiFe2O4 Nanoparticles as Oxygen Carrier in Chemical

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