用于化学循环空气分离的 Brownmillerite 结构 Ca2MnAlO5+δ 的氧非化学计量和缺陷模型,ACS Sustainable Chemistry & Engineering

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用于化学循环空气分离的 Brownmillerite 结构 Ca2MnAlO5+δ 的氧非化学计量和缺陷模型
ACS Sustainable Chemistry & Engineering ( IF 7.1 ) Pub Date : 2022-07-28 , DOI: 10.1021/acssuschemeng.2c03485
Yuan Tian ₁ , Giancarlo Luongo ₂ , Felix Donat ₂ , Christoph R. Müller ₂ , Yngve Larring ₃ , Phillip R. Westmoreland ₁ , Fanxing Li ₁

Affiliation

Brownmillerite 结构的 Ca ₂ MnAlO _5+δ具有出色的储氧能力，可用于化学循环空气分离 (CLAS)，这是一种从空气中生产高纯度氧气的潜在有效方法。为了在 CLAS 中有效地利用这种材料作为氧吸附剂，有必要全面了解其热力学性质和感兴趣的工作范围内的结构-性能关系。在这项工作中，Ca ₂ MnAlO _{5+δ的氧非化学计量比 (δ)}在 440 至 660 °C 的温度和 0.01 至 0.8 atm 的氧分压下，通过热重分析 (TGA) 系统地测量。使用van't Hoff方程计算放氧反应的偏摩尔焓和熵，平均值分别为146.5 ± 4.7 kJ/mol O ₂和162.7 ± 5.1 J/K mol O ₂。实验测量的非化学计量比 (δ) 与应用于两个区域的点缺陷模型很好地拟合，除以预测的平衡P - T曲线。还确定了适当缺陷反应的平衡常数。从缺陷模型得到的主反应的热化学参数、摩尔焓和熵分别为136.9 kJ/mol O ₂和225.3 J/K mol O ₂，与上述值有合理的一致性。缺陷模型的适用性也在高达 4 atm 的较高氧分压环境下得到验证，并显示出对趋势的合理预测。氧非化学计量与缺陷建模相结合的实验研究为氧吸附剂的氧化还原性能提供了有用的见解，并为 CLAS 中氧吸附剂的设计和优化提供了有用的信息。

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Oxygen Nonstoichiometry and Defect Models of Brownmillerite-Structured Ca2MnAlO5+δ for Chemical Looping Air Separation

Brownmillerite-structured Ca₂MnAlO_5+δ has demonstrated excellent oxygen storage capacity that can be used for chemical looping air separation (CLAS), a potentially efficient approach to produce high-purity oxygen from air. To effectively utilize this material as an oxygen sorbent in CLAS, it is necessary to comprehensively understand its thermodynamic properties and the structure–performance relationships in the operating range of interest. In this work, the oxygen nonstoichiometry (δ) of Ca₂MnAlO_5+δ was systematically measured by thermogravimetric analysis (TGA) in the temperature ranging from 440 to 660 °C and under an oxygen partial pressure ranging from 0.01 to 0.8 atm. The partial molar enthalpy and entropy for the oxygen-releasing reaction were calculated using the van’t Hoff equation with an average value of 146.5 ± 4.7 kJ/mol O₂ and 162.7 ± 5.1 J/K mol O₂, respectively. The experimentally measured nonstoichiometry (δ) was well fitted by a point defect model applied in two regions divided by the predicted equilibrium P–T curve. The equilibrium constants for appropriate defect reactions were also determined. The thermochemical parameters, molar enthalpy and entropy for the main reaction, obtained from the defect model were 136.9 kJ/mol O₂ and 225.3 J/K mol O₂, respectively, showing reasonable agreement with the aforementioned values. The applicability of the defect model was also verified at a higher oxygen partial-pressure environment of up to 4 atm and exhibited reasonable prediction of the trend. The experimental studies on oxygen nonstoichiometry combined with the defect modeling provide useful insights into oxygen sorbents’ redox performances and helpful information for the design and optimization of oxygen sorbents in CLAS.

更新日期：2022-07-28

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