In-situ measurement of oxygen release from Ag/SrFeO 3-δ materials for chemical looping catalysis A.R.P. Harrison 1 , S.M. Fairclough 2 , J.M.A. Steele 3,4 , A. Britton 5 , E.A. Willneff 6 , E.J. Marek 1 1 Department of Chemical Engineering and Biotechnology, University of Cambridge, UK, 2 Department of Materials Science and Metallurgy, University of Cambridge, UK, 3 Yusuf Hamied Department of Chemistry, University of Cambridge, UK, 4 Maxwell Centre, Cavendish Laboratory, Cambridge, UK, 5 School of Chemical and Process Engineering, University of Leeds, UK, 6 School of Design, University of Leeds, UK Strontium ferrite (SrFeO 3‑δ ), a non-stoichiometric oxide with a perovskite structure, has attracted considerable interest for applications in chemical looping catalysis where the metal oxide donates oxygen to a reaction, then is re-oxidised in air in a separate step. Particles of SrFeO 3-δ impregnated with a noble metal can be used to catalyse selective oxidation reactions, such as ethylene epoxidation or ethanol dehydrogenation. Recent work [1] has shown that Ag impregnated on the surface of SrFeO 3‑δ readily enhances the rate of oxygen release and re-uptake from the perovskite at temperatures ≤400°C. However, the influence of Ag on the mechanisms of reduction and oxidation of SrFeO 3‑δ remains poorly understood. Here, we performed in-situ measurements of Ag/SrFeO 3-δ during reduction and oxidation using X-ray diffraction (XRD) and electron microscopy ( in-situ TEM), to determine the influence of Ag on oxygen transport within SrFeO 3-δ , and X-ray photoelectron spectroscopy (NAP-XPS) and Raman spectroscopy to determine the oxygen species at the surface of Ag during chemical looping. X-ray diffraction at elevated temperatures (200-900°C) under H 2 showed that the presence of Ag decreased the temperature required for phase transformation from perovskite to brownmillerite structure, SrFeO 2.5 , from ~500°C for bare SrFeO 3-δ to ~300°C for Ag/SrFeO 3‑δ . In-situ TEM measurements demonstrated marked changes in the perovskite non-stoichiometry and crystal structure in the close vicinity to the Ag particles. From NAP‑XPS and operando Raman spectroscopy, multiple monoatomic and diatomic surface oxygen species were detected on Ag during reduction and oxidation, with the fraction of diatomic peroxide and superoxide species markedly increasing during reoxidation, and remaining most strongly bound to the surface during reduction. This project was supported in part by the Henry Royce Institute Researcher Equipment Access Schemes, EPSRC Grant Numbers EP/P022464/1 and EP/R00661X/1 References 1. Harrison et al., 2023, Energy Fuels, 37 , 13, 9487-9499, DOI: 10.1021/acs.energyfuels.3c01263
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