Deactivation behavior of upscaled Fe₂O₃–MgAl₂O₄ oxygen carriers: Impact of operating conditions in chemical looping rWGS

To understand the deactivation mechanisms of oxygen carriers (OC), an industrially prepared Fe₂O₃-MgAl₂O₄ is examined as step up to engineering materials that excel under real-world industrial conditions. This study explores the impact of active gas concentration (H₂/CO₂) and temperature upon performance and resilience of the supported Fe₂O₃ for the chemical looping reverse water–gas shift (CL-rWGS) process. CL-rWGS experiments with a duration of 200 redox cycles reveal that operating temperatures of 1023 K and higher active gas concentrations (32 % and 80 %) result in noticeably reduced activity with longer times on stream, underscoring the impact of gas concentration on the OC's performance. When applying an industrially relevant active gas concentration of 80 %, an optimal temperature of 923 K is identified, at which high CO₂ conversion rates are maintained without significant deactivation (0.05 %/h compared to 1.7 %/h at 1023 K). Rietveld refinement of x-ray diffraction patterns indicates substantial phase transformations, from Fe₃O₄ to FeO and Mg_xFe_1-xAl₂O₄ spinel structures contributing to the OC deactivation. XPS analysis confirms the formation of Mg_xFe_1-xFe_yAl_2-yO₄ phases, indicated by Fe²⁺ and Fe³⁺ peak shifts that suggest strengthened interaction with the support elements. This is corroborated by surface enrichment of Mg and Fe, a decreased Al/Mg ratio, and an increased Fe²⁺/Fe³⁺ ratio. These findings underscore the delicate interplay between temperature, gas concentration, and OC stability, paving the way for material optimization to enhance CO₂ conversion and reactor efficiency in CL-rWGS applications.