Sr substitution effects on atomic and local electronic structure of Ca<sub>2</sub>AlMnO<sub>5+δ</sub>

Kunisada, Yuji; Saito, Genya; Hayami, Kazuki; Nomura, Takahiro; Sakaguchi, Norihito

doi:10.1002/sia.6549

Cited by 4 publications

(9 citation statements)

References 20 publications

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“…In all structures, all axial lengths increased with an increase in the amount of Sr 2+ , which has a larger ionic radius of (1.21 Å; coordination = 7) than Ca 2+ (1.06 Å; coordination = 7). 22,32 On the other hand, the length of the long axes (b-axis in the BM structure and c-axis in the DP structure) was uniformly and significantly reduced with oxygen storage at all the x values. As shown in Figure 4b, this significant reduction in the long axis length is due to the significant flattening of the MnO 6 octahedra.…”

Section: ■ Results and Discussionmentioning

confidence: 94%

“…The structural modification between the storage phase and the release phase on the lower x side falls between the BM structure, n = 1, I 2 mb , and BM structure, n = 3, Imma . Kunisada et al calculated the decrease in the oxygen release and storage temperatures of Sr-doped CAMO, assuming this structural change . They reported that Sr doping lengthened the bond between Mn 4+ and O at the apex of the AlO 4 tetrahedron in the storage phase, preventing Mn 3+ from releasing the Jahn–Teller strain and converting to Mn 4+ .…”

Section: Resultsmentioning

confidence: 99%

“…However, with CAMO, the pressure swing gap becomes wide because of the large hysteresis loop caused by oxygen storage and release. While elemental doping has been theoretically studied as a method for shifting the equilibrium of the oxygen storage and release reaction of Sr-doped CAMO (CSAMO), , it has not been validated experimentally. In general, equal valence ion doping at the A site alters the lattice skeleton.…”

Section: Introductionmentioning

confidence: 99%

“…Doping with larger ions is expected to expand the lattice, weaken the bonds, and facilitate oxygen release. In particular, Sr doping is expected to cause instability in the oxygen storage phase, based on theoretical studies …”

Section: Introductionmentioning

confidence: 99%

“…In particular, Sr doping is expected to cause instability in the oxygen storage phase, based on theoretical studies. 22 In this study, we experimentally investigated CSAMO and revealed the effect of Sr doping on the crystal structure and the oxygen storage/release characteristics. The oxygen storage/ release characteristics of CSAMO were evaluated using a pressure−composition−temperature (PCT) diagram.…”

Section: ■ Introductionmentioning

confidence: 99%

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Sr-Doped Ca₂AlMnO_5 + δ for Energy-Saving Oxygen Separation Process

Tanahashi

Omura

Naya

et al. 2021

ACS Sustainable Chem. Eng.

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Pressure swing adsorption (PSA) is expected to replace the currently used energy-intensive cryogenic distillation process for oxygen separation. For realizing an energy-saving PSA, an oxygen storage material (OSM) with a high oxygen storage capacity and narrow pressure swing gap during reversible oxygen storage and release is necessary. While Ca 2 AlMnO 5 is a promising candidate for PSA, it exhibits a large pressure hysteresis loop during oxygen storage and release. In this study, we investigated the effect of Sr doping of the Ca sites of Ca 2 AlMnO 5 (Ca 2−x Sr x AlMnO 5 ) on the phase compositions and oxygen storage/release performance with the aim of realizing an optimum OSM for the PSA process. From the results of structural refinement, while the oxygen release phase has a Brownmillerite (BM) structure (n = 1) at 0 ≤ x ≤ 1.0, BM (n = 3) and oxygen-defective perovskite were found to be the main structures in the oxygen storage phase at 0 ≤ x < 0.50 and 0.50 ≤ x ≤ 1.0, respectively. The oxygen storage/release temperature obtained from the thermogravimetry curves decreased in the 0 ≤ x < 0.50 range and increased in the 0.50 ≤ x ≤ 1.0 range with increasing x. This difference may be attributed to the structural differences in the storage phase. The pressure− composition−temperature (PCT) analysis by Sieberts' method was applied to the OSM. Although PCT curves exhibited a remarkable decrease in hysteresis in the PSA process as x increased, the difference between onset and offset temperatures for each oxygen storage/release reaction broadened. A new evaluation method to optimize x of Ca 2−x Sr x AlMnO 5 and operating condition in the PSA process using the OSM was also examined. Plots of the pressure change required to release oxygen versus the amount of oxygen extracted allow for the efficient determination of optimal composition and working temperature. Ca 1.2 Sr 0.8 AlMnO 5 (x = 0.80), which exhibited excellent repetition durability, was found to be optimal in this evaluation. The ideal PSA oxygen separation process using Ca 1.2 Sr 0.8 AlMnO 5 has the potential for producing pure oxygen with an energy input of 109.6 kWh/kNm 3 -O 2 , which is a significant energy saving compared to conventional processes.

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Section: ■ Results and Discussionmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Sr-Doped Ca₂AlMnO_5 + δ for Energy-Saving Oxygen Separation Process

Tanahashi

Omura

Naya

et al. 2021

ACS Sustainable Chem. Eng.

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Oxygen production at intermediate temperatures using Ca2AlMnO5+δ double perovskite-type oxides

Pishahang

Larring

Cloete

et al. 2023

J Therm Anal Calorim

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Double-perovskite Ca2AlMnO5+δ exhibits promising oxygen uptake and release capacity at intermediate temperatures (400–700 °C), which makes it an interesting candidate for in situ oxygen production in an integrated gasification combined cycle (IGCC) process. Experiments were conducted at 10 bars by alternating gas feeds of air and various sweep gases to a packed bed filled with 300 g of granular oxygen carrier materials. These realistic operating conditions demonstrated that 15–20% oxygen can be introduced to the sweep gas, which is sufficient for autothermal gasification of solid fuels in IGCC. Argon performed slightly better than CO2 as a sweep gas, presumably because of some CO2 absorption or the higher O2 partial pressure of CO2 that inhibited O2 release. Further O2 concentration increases can be expected from increasing the temperature under reduction by feeding a fuel gas to combust with the released O2, but experiments with H2 did not produce the desired effect because the combustion reaction was too slow at the optimal reactor temperature (~ 600 °C). In general, the reduction stage was more prone to kinetic limitations, as illustrated by a significant decrease in O2 concentration when the sweep flowrate was increased. A longer oxidation stage to fully charge the oxygen carrier also increased O2 concentrations in the sweep, but this requires a process integration such as IGCC where the large quantity of warm depleted air can be effectively utilized. Furthermore, the enthalpy of oxidation of Ca2AlMnO5+δ was obtained from density functional theory modeling, equilibrium conditions in thermogravimetric analysis, packed bed experiments and directly from differential scanning calorimetry. The enthalpy of oxidation obtained by these techniques range from − 166 to − 196 kJ mol−1 O2.

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Tunable Oxygen Intake/Release Characteristics of Brownmillerite-Type Ca₂AlMnO_5+δ Involving Atomic Defect Formations

Iseki

Tamura

Saito

et al. 2021

ACS Appl. Mater. Interfaces

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The oxygen intake/release characteristics were systematically studied for Ca2AlMnO5+δ samples synthesized under precisely controlled oxygen pressures. Both the oxygen storage capacity (OSC) and operating temperature were systematically lowered as the oxygen pressure in the firing atmosphere increased. Notably, the sample fired under a 1% O2 atmosphere exhibited sufficiently large OSC and superior oxygen intake/release kinetics to the pristine sample synthesized in an anaerobic condition. The high-angle annular dark-field scanning TEM observation revealed that the samples contain defects in their atomic arrangement when fired in oxygen-rich atmospheres. This result indicates that the oxygen intake/release characteristics of Ca2AlMnO5+δ are sensitive to the synthesis condition and widely tunable even without chemical substitutions.

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Sr substitution effects on atomic and local electronic structure of Ca₂AlMnO_5+δ

Cited by 4 publications

References 20 publications

Sr-Doped Ca₂AlMnO_5 + δ for Energy-Saving Oxygen Separation Process

Sr-Doped Ca₂AlMnO_5 + δ for Energy-Saving Oxygen Separation Process

Oxygen production at intermediate temperatures using Ca2AlMnO5+δ double perovskite-type oxides

Tunable Oxygen Intake/Release Characteristics of Brownmillerite-Type Ca₂AlMnO_5+δ Involving Atomic Defect Formations

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Sr substitution effects on atomic and local electronic structure of Ca2AlMnO5+δ

Cited by 4 publications

References 20 publications

Sr-Doped Ca2AlMnO5 + δ for Energy-Saving Oxygen Separation Process

Sr-Doped Ca2AlMnO5 + δ for Energy-Saving Oxygen Separation Process

Oxygen production at intermediate temperatures using Ca2AlMnO5+δ double perovskite-type oxides

Tunable Oxygen Intake/Release Characteristics of Brownmillerite-Type Ca2AlMnO5+δ Involving Atomic Defect Formations

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Product

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Sr substitution effects on atomic and local electronic structure of Ca₂AlMnO_5+δ

Sr-Doped Ca₂AlMnO_5 + δ for Energy-Saving Oxygen Separation Process

Sr-Doped Ca₂AlMnO_5 + δ for Energy-Saving Oxygen Separation Process

Tunable Oxygen Intake/Release Characteristics of Brownmillerite-Type Ca₂AlMnO_5+δ Involving Atomic Defect Formations