Migration Mechanism of Lattice Oxygen: Conversion of CO₂ to CO Using NiFe₂O₄ Spinel Oxygen Carrier in Chemical Looping Reactions

Abstract

CO2 resourceful utilization contributes to the goal of carbon neutrality. Chemical Looping Dry Reforming (CLDR) has attracted significant attention as a method for converting CO2 to CO. NiFe2O4 oxygen carrier (OC) is found to be a potential material for CLDR. However, the migration process of lattice oxygen, which are critical for the conversion of CO2 to CO, was not extensively investigated. In this study, the reduction and oxidation degrees of the NiFe2O4 were finely modulated in a thermogravimetric analyzer. The lattice oxygen migration mechanism of the NiFe2O4 in redox cycles was characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and in-situ Raman. The novelty of this paper is clarifying the release-uptake paths of lattice oxygen during CO2 resourceful utilization. The result indicates that the concentration gradient between the surface and the bulk drives the diffusion of lattice oxygen. The stabilization of surface lattice oxygen content is attributed to the rapid migration of O anion, which is closely associated with the movement process of Ni particles inward and outward through the spinel bulk. In addition, a highly reactive chemical reaction interface consisting of lattice oxygen and the corresponding metal atoms is always present on the surface of the oxygen carrier and is confirmed by an in-situ Raman and XPS during the whole process of CLDR. The results of this paper offer reference and basis for further development and design of CLDR using spinel OC.

Keywords

• chemical looping (CL)
• oxygen carrier (OC)
• CO₂ splitting
• lattice oxygen
• NiFe₂O₄