Sustainable iron-based oxygen carriers for hydrogen production – Real-time operando investigation. (September 2019) - De Vos, Yoran
Graphical abstract: Highlights: The solid-state chemistry in the oxygen carrier was investigated in real-time. The Fe/MgAlFeOx oxygen carrier displays sequential reactions from Fe2O3 to Fe/Fe3C. Fe-cations incorporate in the support at tetragonal position when FeII is formed. Fe-cations release from the support when FeII is oxidized/reduced to FeIII/Fe0. Abstract: In this work, a spray-dried Fe-based oxygen carrier with an in situ generated Mg1-x Al2-y Fex+y O4 -support was investigated during packed-bed chemical looping operation with methane at 900 °C. The evolution of the solid-state chemistry taking place in the oxygen carrier material was investigated in real-time with synchrotron X-ray diffraction while the spatial distribution of the phases was investigated using X-ray diffraction computed tomography (XRD-CT). These measurements revealed that some Fe-cations were systematically taken up and released from the spinel support. This take-up and release was shown to be strongly related with the oxidation state of the active phase. Although this take-up and release of Fe-cations decreased the amount of Fe-oxides active in the chemical looping process, the oxygen transfer capacity was still sufficiently high. The microstructure of the oxygen carriers along the length of the packed reactor bed was also investigated with scanning electron microscopy (SEM). The experiments indicate that the MgFeAlOx support with an extra Fe-based active phase is a promising material for oxygen carriers, as it forms a sustainable non-toxic, stable and green alternative to the typical Ni-based oxygen carriers, for hydrogen generation by chemical looping.