Deactivation Study of Fe₂O₃–CeO₂ during Redox Cycles for CO Production from CO₂

Abstract

Deactivation was investigated in Fe 2 O 3 –CeO 2 oxygen storage materials during repeated H 2 -reduction and CO 2 -reoxidation. In situ XRD, XAS, and TEM were used to identify phases, crystallite sizes, and morphological changes upon cycling operation. The effect of redox cycling was investigated both in Fe-rich (80 wt % Fe 2 O 3 –CeO 2 ) and Ce-rich (10 wt %Fe 2 O 3 –CeO 2 ) materials. The former consisted of 100 nm Fe 2 O 3 particles decorated with 5–10 nm Ce 1– x Fe x O 2− x . The latter presented CeO 2 with incorporated Fe, i.e. a solid solution of Ce 1– x Fe x O 2− x, as the main oxygen carrier. By modeling the EXAFS Ce–K signal for as-prepared 10 wt %Fe 2 O 3 –CeO 2, the amount of Fe in CeO 2 was determined as 21 mol %, corresponding to 86% of the total iron content. Sintering and solid–solid transformations, the latter including both new phase formation and element segregation, were identified as deactivation pathways upon redox cycling. In Ce-rich material, perovskite (CeFeO 3 ) was identified by XRD. This phase remained inert during reduction and reoxidation, resulting in an overall lower oxygen storage capacity. Further, Fe segregated from the solid solution, thereby decreasing its reducibility. In addition, an increase in crystallite size occurred for all phases. In Fe-rich material, sintering is the main deactivation pathway, although Fe segregation from the solid solution and perovskite formation cannot be excluded.