Evolution of nanoscale morphology in single and binary metal oxide microparticles during reduction and oxidation processes

Qin, Lang; Majumder, Ankita; Fan, Jonathan A.; Kopechek, David

doi:10.1039/c4ta04338c

Cited by 67 publications

(44 citation statements)

References 36 publications

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“…Subsequently, the NiFe alloys were reoxidized by O 2 to form NiFe 2 O 4 . Due to differences in the oxidation and ion diffusion rates of Ni and Fe, uniform NiFe microparticles are transformed into particles with a NiO‐rich core and a Fe 2 O 3 ‐rich shell during oxidation . So, the phase segregation of NiFe 2 O 4 gradually occurred with the increase of redox cycles.

Reduction : {NiFe}_{2} {normalO}_{4} + {normalH}_{2} \to Ni + {Fe}_{3} {normalO}_{4} + {normalH}_{2} O \to NiFe + {normalH}_{2} O

Oxidation : NiFe + {normalO}_{2} \to {NiFe}_{2} {normalO}_{4}

…”

Section: Resultsmentioning

confidence: 99%

“…Figure shows the surface Fe atomic ratio of fresh and spent NiFe 2 O 4 OCs based on the EDS‐mapping results in Figure and . Due to no Ni migration in the redox reactions, atomic ratio of Fe/(Fe + Ni) was used to quantify the Fe concentration changes on the surface of NiFe 2 O 4 OCs. Compared with the EDX‐mapping images in Figure , the surface concentration of Ni, Ce, and Zr decreased significantly for CeZrO 2 –NiFe 2 O 4 and ZrO 2 –NiFe 2 O 4 after ten redox cycles, as shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…However, there have been few studies focusing on the Fe segregation of NiFe 2 O 4 OCs in the CL process. The literature reported that a structure with a NiO‐rich core and an Fe 2 O 3 ‐rich shell was produced from homogeneous FeNi particles during the redox process . The higher diffusion coefficient of Fe than that of oxygen was recognized as an important driving force for Fe segregation [4a,20].…”

Section: Introductionmentioning

confidence: 99%

“…The literature reported that a structure with a NiO‐rich core and an Fe 2 O 3 ‐rich shell was produced from homogeneous FeNi particles during the redox process . The higher diffusion coefficient of Fe than that of oxygen was recognized as an important driving force for Fe segregation [4a,20]. Consequently, it is reasonable to expect that abundant oxygen vacancies can improve the surface stability of NiFe 2 O 4 .…”

Section: Introductionmentioning

confidence: 99%

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Effect of Supports on the Redox Performance of NiFe₂O₄ in a Chemical Looping Process

Zeng

Zhang

et al. 2019

Energy Tech

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NiFe2O4 oxygen carrier (OC) presents higher oxygen carrying capacity than single metal oxides (NiO and Fe2O3). However, the redox ability of NiFe2O4 gets deactivated due to phase segregation. Herein, the investigation of the effect of supports (CeO2, CeZrO2, and ZrO2) on the phase stability and the redox performance of NiFe2O4 during the chemical looping (CL) process are presented. The structure of NiFe2O4‐based OCs is characterized using different characterization methods. The CL reaction is conducted in a fixed‐bed reactor at 900 °C under alternate 5% CO/N2 and 5% O2/N2 atmospheres. The results indicate that the redox performance and the phase stability of NiFe2O4‐based OCs are significantly affected by the supports. According to experimental results, CeO2 can improve the oxygen mobility of NiFe2O4. The CeO2–NiFe2O4 OC has the best performance in terms of both recyclability and phase stability during the redox cycles. The results show that CeO2–NiFe2O4 can reduce the tendency of Fe segregation due to the high concentration of oxygen vacancies. It can be reduced and reoxidized to the original crystalline phase of NiFe2O4. Nevertheless, the CeZrO2–NiFe2O4 and ZrO2–NiFe2O4 OCs have drawbacks related to serious sintering and phase segregation into Fe2O3.

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Reduction : {NiFe}_{2} {normalO}_{4} + {normalH}_{2} \to Ni + {Fe}_{3} {normalO}_{4} + {normalH}_{2} O \to NiFe + {normalH}_{2} O

Oxidation : NiFe + {normalO}_{2} \to {NiFe}_{2} {normalO}_{4}

…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Effect of Supports on the Redox Performance of NiFe₂O₄ in a Chemical Looping Process

Zeng

Zhang

et al. 2019

Energy Tech

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“…9, probably due to the iron migration onto the surface of oxygen carriers. Qin et al (2014) analyzed the core-shell structure formations of FeNi microparticles during the cyclic oxidation-reduction reaction, and reported that the outward iron ions diffusion was faster than the inward oxygen diffusion in iron oxide. Hence, the preliminarily simplified mechanism for iron cations diffusion of FeAl320-S10 and FeTi320-S0 pellets during reduction and oxidation operations are demonstrated as Fig.…”

Section: Resultsmentioning

confidence: 99%

Preparation of Fe2O3/Al2O3 and Fe2O3/TiO2 Pellets as Oxygen Carrier for Chemical Looping Process

Lin

et al. 2017

Aerosol Air Qual. Res.

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Fe-based oxygen carriers supported by Al 2 O 3 and TiO 2 were prepared as pellets for chemical looping combustion in this study. Over 90% conversions were obtained for most experiments operated in the TGA; however, experiments conducted with FeTi320 pellets exhibited higher conversions than those with FeAl320. The prepared pellets sintered at higher temperatures always exhibited higher crush strength. The crush strength of prepared FeAl320 and FeTi320 pellets were decreased for experiments conducted with greater starch content, because the more pore spaces are formed in the original places of the starch grains. For experiments conducted in the fixed bed reactor, the prepared pellets exhibited relatively high conversion. The conversions of FeTi320 were remained to be about 80% with increasing starch content because high porosity (approximately 50%) was formed for 0-20% starch contents of FeTi320 pellets after 10 redox cycles. Less porosity was formed after 20 redox cycles for experiments conducted with FeAl320 pellets prepared with higher starch contents. Therefore, the conversion of FeAl320 pellets was elevated with increasing starch content. Iron content for inner part of prepared pellets was significantly decreased after operated for 20 redox cycles, while iron content for outer part of pellets were increased. It is suggested that the iron ions may diffuse onto the surface of oxygen carriers to react with oxygen during the oxidation period.

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Tungsten's Role in Enhancing Sintering Resistance of Fe‐W Hierarchical Foams during Redox Cycling

Chen,

Pennell,

Dunand

2024

Adv Funct Materials

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Directional freeze‐cast Fe‐W lamellar foams with 10–33 at.% W show distinct microstructural evolutions during steam/hydrogen redox cycling between oxidized and reduced states at 800 ⁰C, depending on W concentration. The Fe‐18 W and Fe‐25 W foams exhibit a sufficient volume fraction of W‐rich phases – λ‐Fe2W to inhibit sintering for α‐Fe in the reduced state and FeWO4 to inhibit sintering for Fe3O4 in the oxidized state – thus forming ligaments comprising two phases (Fe/λ‐Fe2W and Fe3O4/FeWO4, respectively). In contrast, a Fe‐10 W foam with a lower volume fraction of W‐containing phases (λ‐Fe2W and FeWO4) shows lamellae densification as well as core‐shell structure formation, due to Fe outward diffusion during oxidation. While higher W concentration enhances the stability of lamellar structure in Fe‐W foams, degradation still occurs, via buckling of lamellae and swelling of foams after extensive cycling. In situ XRD characterization shows that W addition has a minor effect on the oxidation process but slows reduction due to the sluggish kinetics of FeWO4 reduction. This influence is mitigated by the formation of nanocrystalline W‐rich phases due to the chemical vapor transport (CVT) mechanism during the reduction of FeWO4 to boost the reaction kinetics during redox cycling.

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Evolution of nanoscale morphology in single and binary metal oxide microparticles during reduction and oxidation processes

Abstract: Metal oxide composites are enabling materials for many energy conversion systems such as chemical looping and photocatalysis.

Cited by 67 publications

References 36 publications

Effect of Supports on the Redox Performance of NiFe₂O₄ in a Chemical Looping Process

Effect of Supports on the Redox Performance of NiFe₂O₄ in a Chemical Looping Process

Preparation of Fe2O3/Al2O3 and Fe2O3/TiO2 Pellets as Oxygen Carrier for Chemical Looping Process

Tungsten's Role in Enhancing Sintering Resistance of Fe‐W Hierarchical Foams during Redox Cycling

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Evolution of nanoscale morphology in single and binary metal oxide microparticles during reduction and oxidation processes

Abstract: Metal oxide composites are enabling materials for many energy conversion systems such as chemical looping and photocatalysis.

Cited by 67 publications

References 36 publications

Effect of Supports on the Redox Performance of NiFe2O4 in a Chemical Looping Process

Effect of Supports on the Redox Performance of NiFe2O4 in a Chemical Looping Process

Preparation of Fe2O3/Al2O3 and Fe2O3/TiO2 Pellets as Oxygen Carrier for Chemical Looping Process

Tungsten's Role in Enhancing Sintering Resistance of Fe‐W Hierarchical Foams during Redox Cycling

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Effect of Supports on the Redox Performance of NiFe₂O₄ in a Chemical Looping Process

Effect of Supports on the Redox Performance of NiFe₂O₄ in a Chemical Looping Process