Oxygen release–absorption properties and structural stability of Ce0.8Fe0.2O2−x

Abstract

Oxygen release–absorption properties and structural stability of Ce–Fe mixed oxides (Ce0.8Fe0.2O2−x) with different calcination temperatures (600–1000 °C) were investigated and correlated to their oxygen storage capacity. Iron ions could be incorporated into the CeO2 lattice to form a solid solution after calcination at low temperatures, but such solid solution was unstable under high-temperature thermal treatments. High-temperature (≥800 °C) calcination resulted in the appearance of exposed Fe2O3 phases on the surface of the solid solution, and this structural evolution finally affected the reduction behavior. The Fe3+ reduction from the Ce–Fe oxide solid solution was easier than the bulk Fe2O3 particles, while the small Fe2O3 particles in close contact with CeO2 could enhance the reducibility of cerium oxides. The strong interaction between the exposed small Fe2O3 particles and the solid solution made the Ce–Fe mixed oxides possess good reduction stability and high oxygen storage capacity (OSC) even after repeated redox treatments. Such interactions were absent toward the physically mixed sample. An unusual enhancement on the reducibility of Ce–Fe mixed oxides was observed after a successive redox treatment. Large oxygen evolution appeared at around 600 °C for the recycled samples, and the OSC rose to 1.31 mmol-O2/g after six redox cycles. The XRD, Raman, and TEM analyses revealed that the material structure of the mixed oxides was stabilized to have an inter-region between the Fe2O3 particles and the solid solution after the redox treatment. It was concluded that such microstructural evolutions of composite particle from solid solution under redox conditions brought beneficial property to the OSC of the Ce–Fe mixed oxides.