Mössbauer Study of (Sr,Ca)(Fe,Co)O_3−δ Applied to CO₂ Absorption at High Temperatures

Abstract

CO₂ absorption properties and microstructure of the perovskite (Sr,Ca)(Fe,Co)O_3−δ with different compositions were characterized by TGA, XRD, FT-IR and Mössbauer spectroscopy (TMS and EMS). (Sr_0.5Ca_0.5)(Fe_0.5Co_0.5)O_3−δ showed the highest absorption of CO₂ in the temperature range of 550°C to 850°C in the series of (Sr,Ca)(Fe,Co)O_3−°. In the Mössbauer spectra of the oxides after CO₂ absorption, a new sextet of Fe^III spinel compounds appeared in addition to two broad sextets of Fe^III species at octahedral and tetrahedral sites of brownmillerite structured CaFeO_2.5. It is found directly by EMS that Co atoms in the oxides prefer the tetrahedral sites as +3 valence state. The oxides with high activity of CO₂ absorption showed an intense vibration band in the FT-IR spectra. These results suggested that the zigzag structure of the mixed oxides is helpful for understanding the rapid absorption of CO₂.