Investigation of perovskite supported composite oxides for chemical looping conversion of syngas

In typical chemical looping processes, a transition metal oxide based oxygen carrier is used to indirectly convert carbonaceous fuels into concentrated CO2 and carbon free products through cyclic redox reactions. Among the various oxygen carrier candidates, iron oxide represents a promising option due to its abundance, low cost, and unique thermodynamic properties. A key challenge for ferrite based oxygen carriers resides in their low redox activity. In the current study, composite iron oxides with three types of mixed ionic–electronic conductive (MIEC) supports, i.e. lanthanum strontium ferrite (Sr-substituted lanthanum ferrite or LSF), barium cerium ferrite (Ce-substituted barium ferrite, BCF) and calcium titanate ferrite (Fe-substituted calcium titanate, CTF), are synthesized using solid state reaction (SSR) and sol–gel methods. Among the three MIEC materials, CTF support is found to possess superior structural stability. MIEC supported oxygen carriers are found to be significantly more active than a reference, yttrium-stabilized zirconia (YSZ) supported oxygen carrier. Higher support conductivity and smaller iron oxide precursor sizes generally lead to enhanced oxygen carrier activity. In contrast, surface area of the oxygen carrier is weakly correlated with its redox activity. CTF, although less conductive compared to BCF and LSF, is stable and sufficiently effective in shuttling active O2− and electrons for syngas oxidation and iron oxide regeneration. Therefore, CTF supported ferrites can potentially be a cost-effective oxygen carrier candidate for chemical looping processes. Further improvements in redox activity of the oxygen carriers can be achieved through iron oxide particle size reduction and support conductivity enhancement.