Oxygen sorption/desorption behavior and crystal structural change for SrFeO3−δ

• Oxygen desorption and structural changes for SrFeO3−δ were investigated.
• Phase transitions of SrFeO3−δ were observed in nitrogen, depending on temperature.
• Sr8Fe8O23 transferred to Sr2Fe2O5 via Sr4Fe4O11 with increasing temperature.
• Isothermal oxygen sorption/desorption of SrFeO3−δ was examined for the HT-PSA.
• Actual oxygen separation from atmospheric air was succeeded at 600 °C.

This paper aims to elucidate oxygen sorption/desorption behavior accompanying with phase transition for perovskite-type oxide of SrFeO3−δ, as a function of temperature and oxygen partial pressure. Oxygen desorption of SrFeO3−δ in the temperature range of 100–800 °C was examined in terms of oxygen non-stoichiometry and crystal structural change, by means of thermogravimetric analysis and Mössbauer spectroscopy. In the case of oxygen desorption in nitrogen, the oxygen content of SrFeO3−δ was reduced in a stepwise manner. Thus, three phases having oxygen-vacancy-ordered structures were observed, depending on temperature; Sr8Fe8O23 (SrFeO2.875) below 300 °C, Sr4Fe4O11 (SrFeO2.75) at 300–400 °C, and Sr2Fe2O5 (SrFeO2.5) above 400 °C. In contrast, in the case of oxygen desorption in air, the oxygen content decreased monotonically with increasing temperature without appearance of any stable phases. Furthermore, the isothermal oxygen sorption/desorption behavior of SrFeO3−δ was examined to evaluate the capability as an oxygen sorbent for the high-temperature pressure-swing adsorption (HT-PSA) process. The sample sorbed oxygen in air and desorbed it in nitrogen reversibly at a constant temperature above 300 °C. The oxygen-storage capacity based on the reversible weight change exhibited rather large value above 400 °C, due to the large difference in its oxygen content between in air and in nitrogen. Actual oxygen separation from atmospheric air was performed at 600 °C by means of the small-scale HT-PSA apparatus loaded with the SrFeO3−δ pellet-sample. The result suggests that SrFeO3−δ is one of potential oxygen sorbents for the HT-PSA process.