Enhanced activity of Mg-Fe-O ferrites for two-step thermochemical CO2 splitting

Abstract

Fe-based ferrites have been investigated as the most promising and active redox materials for two-step thermochemical CO2 splitting. Reactions are conducted in a two-step cycle, in which the ferrites are generally reduced at 1400 °C in an inert atmosphere, then the reduced ferrites are re-oxidized by reacting with CO2 at 1000 °C to produce CO. In this work, Mg-Fe-O ferrites (designated as FM-x, x denotes as the mole fraction of Fe2O3 to MgO + Fe2O3) were screened for activity in two-step thermochemical CO2 splitting. Ferrites were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and Mössbauer spectroscopies. The self-regenerative function and internal reaction, which are responsible for the initial higher CO production rate and a greater utilization of the bulk ferrites, respectively, were confirmed for Mg-Fe-O ferrites. Consequently, the self-regenerative FM-0.2 with internal reaction possesses a 2.2 times higher CO yield as compared with that of FM-0.5. Kinetic analysis was conducted in consideration of various solid state reaction models, and bulk diffusion, which is an indication of internal reaction, was found to be the crucial factor for the accessibility of the bulk redox species.