Dynamics of the Lattice Oxygen in a Ruddlesden–Popper-type Sr3Fe2O7−δ Catalyst during NO Oxidation

In situ observation is a powerful and interesting technique for the characterization of functional materials in their working states. In this study, we used in situ dispersive X-ray absorption fine structure (DXAFS) measurements to observe the lattice oxygen dynamics in SrFeO 3−δ and Sr 3 Fe 2 O 7−δ during NO oxidation. The white-line intensities of Sr K-edge XAFS reflect the concentration of oxygen vacancies, and the lattice oxygen dynamics during NO oxidation are observed. Using a kinetics model, the rate-determining step (RDS) for NO oxidation was found to be an oxygen migration step. The activation energy obtained from the Arrhenius plots for Sr 3 Fe 2 O 7−δ is much smaller than that obtained for SrFeO 3−δ . Sr 3 Fe 2 O 7−δ with a Ruddlesden–Popper-type layered perovskite can release oxygen with relatively small structural rearrangements. In contrast, SrFeO 3−δ requires a significant rearrangement of oxygen vacancies to form the brownmillerite phase and the transformation restricts the oxygen release rate. The oxygen storage profiles with O 2 also show that the RDS is the oxygen migration step, although the dissociative adsorption of O 2 suppresses oxygen storage at low temperatures. The lattice oxygen dynamics obtained from the DXAFS measurements, which cannot be obtained from steady-state kinetics experiments, reveal the importance of the perovskite structure for NO oxidation.