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.
For the successful molten salt synthesis of La0.8Sr0.2MnO3, the salt cation is more influential than the anion. With a KNO3 solvent, pure phase LSM nanoparticles are synthesized at 600 °C in 1 hour.
We have studied the reversible uptake and release of oxygen in the layered metal oxide system AB2O4 for A = Lu, Yb, Y, and In to understand their suitability as oxygen storage materials.
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