Exploring the migration and transformation of lattice oxygen during chemical looping with NiFe2O4 oxygen carrier

Abstract Chemical looping (CL) technology using an oxygen carrier (OC) offers a versatile platform to convert various fuels (e.g., CH4, coal, and biomass) to value-added products (e.g., heat, syngas, and H2) in a clean and efficient approach. Currently, the migration and transformation mechanisms of lattice oxygen in spinel OCs were not extensively investigated, which are considered the cornerstone of OC. In this work, the release-uptake paths of lattice oxygen and the chemical reaction laws at interface were studied in detail using a composite metal oxide (NiFe2O4) as an OC through (in-situ) XPS technology coupled with fixed bed experiments. Mechanistic studies indicate that the chemical reaction interface is fixed on the surface of OC particles, and the concentration gradient between the surface and the bulk drives the transmission of lattice oxygen to achieve the reduction or oxidation of OC. Additionally, an important hydroxyl ions formation process of OC is confirmed by an in-situ XPS.