Solvent-free, improved synthesis of pure bixbyite phase of iron and manganese mixed oxides as low-cost, potential oxygen carrier for chemical looping with oxygen uncoupling

Chemical looping with oxygen uncoupling (CLOU) is the tendency of releasing gaseous oxygen of an oxygen carrier upon heating, which is the key property for the efficient and cleaner combustion of solid fuels for their wide exploitation for thermal power applications. The solvent-free, improved synthesis method was developed for the synthesis of pure bixbyite, FeMnO₃ (Ia3-, a=b=c=0.94 nm) as a low-cost, oxygen carrier by exposing of the abundantly available precursors (Fe₃O₄ and MnO) under inert- or reduction- atmosphere followed by air at 900°C. The bixbyite FeMnO₃ showed the enhanced, stable multi-cycle CLOU performance than that of the physical mixture and it is converted into FeMn₂O₄ after the complete exhaustion of reactive oxygen under CLOU conditions. FeMnO₃ showed the uniform elemental distribution of Fe, Mn and O, which facilitate the regeneration in air upon heating for multi-cycle performance. 3.2 wt.% of reactive oxygen can be obtained compared to the mass of FeMnO₃ which is almost equal to the theoretical value under CLOU conditions. The lattice of FeMnO₃ is altered linearly above 100°C with the increase of temperature, however; without the decomposition of the bixbyite phase and it was reinstated virtually upon cooling in air.