Oxygen Storage Properties of La_1–xSr_xFeO_3−δ for Chemical-Looping Reactions—An In Situ Neutron and Synchrotron X-ray Study

Abstract

Oxygen storage materials (OSMs) provide lattice oxygen for a number of chemical-looping reactions including natural gas combustion and methane reforming. La1–x Sr x FeO3−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 La1–x Sr x FeO3−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 La2/3Sr1/3FeO3−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.

Evidence for oxygen vacancy manipulation in La1/3Sr2/3FeO3−𝜹 thin films via voltage controlled solid-state ionic gating

“…The structural change in the LSFO channel is attributed to oxygen vacancy formation within LSFO, consistent with previous works that demonstrated oxygen loss leads to a lattice expansion in LSFO. 42,43 Comparing these results to previous experiments of uncapped LSFO films, 44 the changes in the LSFO lattice parameter are smaller and take longer than a single layer of an uncapped LSFO film of similar thickness heated to 200 • C. This difference is thought to arise from the GDC forming a barrier layer that partially inhibits the reduction of LSFO. Without the presence of the GDC layer, the oxygen ions are more readily desorbed from the surface.…”

Life cycle assessment of optimised chemical looping air separation systems for electricity production

“…Here, the model assumes that the solid in the dual circulating fluidized bed consists of active material only, i.e. no support material is added to the oxygen carrier material (Taylor et al, 2016). The net electrical efficiency, excluding the flue gas cleaning requirements, is 38.9 %.…”

Combined Syngas and Hydrogen Production using Gas Switching Technology

“… 50 Perovskite-based metal oxides have demonstrated good performance for the production of syngas from CH 4 . 51 − 54 Perovskites have the general formula of ABO 3 , where A represents a rare earth metal and/or an alkaline earth metal, and B is a transition metal. 55 , 56 Perovskites generally possess good redox properties under the appropriate temperature and pressure conditions, 55 , 56 offer more resistance to carbon deposition, and are thermodynamically suitable to convert CH 4 to syngas.…”