| This study follows two methods to achieve a modified CaMnO 3-delta structure with higher oxygen capacity and stability. The first method is replacement of manganese with iron as a cheaper alternative and the second method is size effect investigations of A-site dopants on CaMn 0.9Fe0.1O3-delta and its oxygen capacity and stability. Solid state reaction followed by mechanical extrusion is used as the preparation method. All synthesized perovskites are characterized by TGA and XRD analyses. The samples of highest oxygen capacity and stability are further characterized by SEM and BET analyses. Oxygen uncoupling behavior and reactivity of these samples are also examined using a fluidized bed reactor performing Chemical Looping Combustion. The temperature effect is also investigated during chemical looping process at temperatures of 800, 850, 900 and 950 °C.;In the first method, since calcium could not be incorporated in the structure, strontium is used as the A-site cation. SrFeO3-delta has shown to be more stable than CaMnO3-delta. However, because of low oxygen capacity, it is doped on the A-site (La and Ba) and B-site (Al, Ti, Mn, Co) by 10 mol% (Sr0.9La0.1FeO3-delta, Sr0.9Ba0.1FeO3-delta, SrFe0.9Al 0.1O3-delta, SrFe0.9Ti0.1O3-delta , SrFe0.9Mn0.1O3-delta, SrFe 0.9Co0.1O3-delta). Results reveal that manganese doped structure (SrFe0.9Mn0.1O3-delta) has the highest oxygen capacity. Adding more manganese to the structure increases the oxygen capacity even further. The best iron-based structure has 30 mol% manganese, doped on the B-site, having 28% mass change in an inert atmosphere (SrFe0.7Mn0.3O3-delta, SFM73) and high stability.;Results of conducted experiments in second method demonstrated that Strontium doped perovskite (Ca0.9Sr0.1Mn0.9Fe 0.1O3-delta, CS91MF91) is the best synthesized oxygen carrier among all synthesized manganese and iron-based perovskites. This material shows excellent oxygen uptake and release (1.78 wt. %) and high stability. The reactivity and oxygen uncoupling behavior experiments of SFM73 and CS91MF91 show no uncoupling behavior in the synthesized perovskites, nearly complete methane conversion for SFM73 and complete methane conversion for CS91MF91. The synthesized perovskites also possess high stability and no agglomeration tendency. |
