Effect of iron substitution on redox kinetics of CaMn0.875-xFexTi0.125O3-δ

Aiming for a technology with high efficiency and low cost for carbon capture, chemical looping combustion (CLC) shows a promising potential. Unlike other pre-combustion and post-combustion techniques, it allows the inherent separation of CO2 during the fuel combustion. Fuel combustion happens in a nitrogen free reactor (fuel reactor) thanks to the direct reaction of the fuel with oxygen released from a solid oxygen carrier material (OCM). The spontaneous release of oxygen by the OCM prior to the fuel combustion is very efficient and is referred to as the chemical looping oxygen uncoupled (CLOU) effect. There are several important requirements to the OCM during reducing and oxidation (redox) cycles: a high oxygen capacity, high redox kinetics with both air and fuel and good mechanical properties. Furthermore it should be low cost and have a low toxicity. From expensive and carcinogenic nickel oxide to low cost ore, several hundreds of materials based on Ni, Cu, Fe, Mn, Co were studied as potential OCM for CLC. Lately, a significant interest has been shown to mixed OCM, especially to materials derived from the calcium manganite CaMnO3-δ perovskite. Substitution of Mn by magnesium, titanium or a combination of both were investigated. CaMn1-xTixO3-δ has proved to have catalytic activity with respect to CH4 reduction. Stability of the perovskite structure is enhanced by Ti substitution. Also it has been demonstrated that CaMn0.875Ti0.125O3-δ shows promising performance as an OCM for CLOU. In this study a careful tailoring of the chemical composition of CaMn0.875.xFexTi0.125O3-δ is investigated in order to control the release and uptake of oxygen. The latter were measured using cyclic thermogravimetric measurements (TG) under redox atmospheres, simulating the conditions during CLC operation. It is shown that iron substitution improves the redox kinetics. The effect of iron substitution on the mechanical properties will also be reported.