Oxygen Storage Properties of La1–xSrxFeO3−δ for Chemical-Looping Reactions—An In Situ Neutron and Synchrotron X-ray Study

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• 作者：Daniel D. Taylor ; Nathaniel J. Schreiber ; Benjamin D. Levitas ; Wenqian Xu ; Pamela S. Whitfield ; Efrain E. Rodriguez
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：June 14, 2016
• 年：2016
• 卷：28
• 期：11
• 页码：3951-3960
• 全文大小：605K
• 年卷期：0
• ISSN：1520-5002

文摘

Oxygen storage materials (OSMs) provide lattice oxygen for a number of chemical-looping reactions including natural gas combustion and methane reforming. La_1–xSr_xFeO_3−δ has shown promise for use as an OSM in methane reforming reactions due to its high product selectivity, fast oxide diffusion, and cycle stability. Here, we investigate the structural evolution of the series La_1–xSr_xFeO_3−δ for x = 0, 1/3, 1/2, 2/3, and 1, using in situ synchrotron X-ray and neutron diffraction, as it is cycled under the conditions of a chemical-looping reactor (methane and oxygen atmospheres). In the compositions x = 1/3, 1/2, 2/3, and 1, we discover an “envelope”, or temperature range, of oxygen storage capacity (OSC), where oxygen can easily and reversibly be inserted and removed from the OSM. Our in situ X-ray and neutron diffraction results reveal that while samples with higher Sr contents had a higher OSC, those same samples suffered from slower reaction kinetics and some, such as the x = 1/2 and x = 2/3 compositions, had local variations in Sr content, which led to inhomogeneous regions with varying reaction rates. Therefore, we highlight the importance of in situ diffraction studies, and we propose that these measurements are required for the thorough evaluation of future candidate OSMs. We recommend La_2/3Sr_1/3FeO_3−δ as the optimal OSM in the series because its structure remains homogeneous throughout the reaction, and its OSC “envelope” is similar to that of the higher doped materials.