Hydrogarnet-Derived Porous Polyhedral Particles of SrFeO_3-δ Perovskite

Introduction of open mesoporosity into microparticles with a robust morphology provides a high active surface area together with good thermal stability and shows benefit in various applications at high temperatures. Recently, nonstoichiometric Sr–Fe perovskites with an oxygen release/absorption capability have attracted interests as an oxidation catalyst operated at elevated temperatures. Here, we demonstrate the topotactic synthesis approach to fabricate mesoporous microparticles of SrFeO 3−δ with monodispersibility as well as rhombic dodecahedral morphology from the correspondent hydrogarnet precursor (Sr 3 Fe 2 (OH) 12 ) prepared by the hydrothermal reaction. Relationship between synthetic conditions and the formed crystal morphology has been systematically explored, which discloses that the crystallization of hydrogarnet can take place at as low as 40 °C. On heating, the dehydration of Sr 3 Fe 2 (OH) 12 gives rise to phase separation into Sr(OH) 2 and SrFeO 3−δ via a transient phase of “oxyhydrogarnet”. Selective removal of the Sr(OH) 2 -derived phase leaves three-dimensionally interconnected mesopores in individual polyhedral microparticles. Meanwhile, further increase of the heat-treatment temperature sets off the reaction between the two separated phases, ending up in nonporous polyhedral particles composed of Ruddlesden–Popper-type layered perovskite (Sr 3 Fe 2 O 7−δ ) at 1200 °C. The mesoporous SrFeO 3−δ polyhedral microparticles exhibit an enhanced catalytic performance of CO oxidation superior to the nonporous counterparts, which is associated with the stimulated oxygen release capability owing to mesoporosity rather than the oxygen uptake rate.