Microstructural study of the CO2 absorption in SrxCa1−xFe0.5Co0.5O3−δ

The absorption of CO2 in SrxCa1−xFe0.5Co0.5O3−δ perovskite (x=0.95, 0.5) has been studied with the aid of 57Fe Mössbauer Spectroscopy. Due to their remarkable CO2 absorption capability at high temperature, SrxCa1−xFe0.5Co0.5O3−δ-type compounds may find application in reducing the industrial CO2 output that is a major source of the global green house effect. The Mössbauer spectra of Sr0.5Ca0.5Fe0.5Co0.5O3−δ and Sr0.95Ca0.05Fe0.5Co0.5O3−δ were markedly different before as well as after CO2 absorption, indicating different microenvironments and electronic structure of the Fe atoms in the lattice. The Ca-rich compound absorbed CO2 much faster and had twice as much total CO2 absorption capacity than the other one. The high absorption rate was attributed to the orthorhombic layered brownmillerite structure of Sr0.5Ca0.5Fe0.5Co0.5O3−δ, while it was concluded that the cubic structure of Sr0.95Ca0.05Fe0.5Co0.5O3−δ, stabilized by higher O-stoichiometry, is unpreferred for CO2 absorption. In agreement with X-ray diffraction (XRD) data, the reaction 2(Sr,Ca)(Fe,Co)O2.5+CO2→(Sr,Ca)CO3+(Sr,Ca)(Fe,Co)2O4 is proposed to account for the absorption process.