<i>In Situ</i> and Simultaneous Observation of Palladium Redox and Oxygen Storage/Release in Pd/Sr&ndash;Fe&ndash;O Perovskite Catalysts Using Dispersive XAFS

Abstract

We have succeeded in in situ and simultaneously observing the redox reaction of palladium and the oxygen storage/release process in a newly developed palladium-promoted SrFeO (Pd/SrFeO) catalyst during redox-gas cycles using dispersive X-ray absorption fine structure (XAFS) analysis at 673 K with a time resolution of less than 20 ms. The Pd/SrFeO catalyst, which exhibits high performance for automotive emission control, has a unique "multi-phase-domain" structure, where a single grain is composed of nano-sized domains of three phases: SrFeO 3¹¤ , Sr 4 Fe 6 O 13¹¤ and SrFe 12 O 19¹¤ . In situ observation has shown a strong correlation between the redox of the palladium and the oxygen storage/release in the Pd/SrFeO catalyst, and the correlation factors differ between the reduction and oxidation reactions. The oxide phases exhibit a type of "oxygen buffer" effect in the oxidation cycle and delay the formation of PdO, resulting in the high performance of the catalyst.

Oxygen Storage Property and Chemical Stability of SrFe1–xTixO3−δ with Robust Perovskite Structure

“…Although the TG analysis can roughly evaluate the oxygen storage and release rates at a low time resolution (in the order of seconds), it is unfortunately inadequate for measuring the faster rates of SrFe 1– x ­Ti x ­O 3−δ . Instead, we measured these rates of SrFe 1– x ­Ti x ­O 3−δ by using in situ DXAFS which has a much higher time resolution (in the order of milliseconds) Figure S3 shows the Sr K-edge X-ray absorption near edge structure (XANES) spectra of the as-prepared SrFeO 3−δ and Sr 2 Fe 2 O 5 .…”

Synchrotron Radiation Shed Light to <i>In Situ </i>and Dynamic Observation of High-Temperature Processes

“…Furthermore, the atomic structure and microstructure of the catalyst are extensively investigated. Based on these results, we proposed reaction mechanisms in terms of the correlation between the redox of palladium and the oxygen storage/release during redoxgas cycles, which is crucial information for understanding the mechanism of the high performance of not only the Pd/Sr-Fe-O catalyst but also other TWCs [19,20].…”

“…Pd/Sr-Fe-O Catalyst [19,20] We have developed the Pd/Sr-Fe-O catalyst which exhibits high performance for automotive emission control. The Sr-Fe-O oxide support has a unique "multiphase-domain" structure, where a single grain is composed of nano-sized domains of three phases: SrFeO 3−δ , Sr 4 Fe 6 O 13−δ , and SrFe 12 O 19−δ (Fig.…”

Time-Resolved Observation of Phase Transformation in Fe–C System during Cooling via X-ray Absorption Spectroscopy

“…DXAFS is a technique for time-resolved observation of XAFS spectra with white X-rays converged on to a specimen, which requires no scanning of the energy of X-rays, and has been applied for in situ obsenvation of reactions. 12) The specimens were heated by a laser, and changes in the iron atomic structures in the FeC system were observed during cooling after terminating the heat treatment. Through the proposed technique, the detection of different behaviors during the change of atomic structures at the SRO scale, was studied.…”