Nature and Redox Properties of Iron Sites in Zeolites Revealed by Mössbauer Spectroscopy

• Published in: ChemPlusChem (Weinheim, Germany) Vol. 89; no. 5; pp. e202300543 - n/a
• Main Authors: Kornas, Agnieszka, Mlekodaj, Kinga, Tabor, Edyta
• Format: Journal Article
• Language: English
• Published: Germany 01.05.2024
• Subjects: iron sites; methane; Mössbauer spectroscopy; N2O decomposition; zeolites; methane; zeolites; N2O decomposition; iron sites; Mössbauer spectroscopy
• ISSN: 2192-6506; 2192-6506
• DOI: 10.1002/cplu.202300543

Iron‐containing zeolite‐based catalysts play a pivotal role in environmental processes aimed at mitigating the release of harmful greenhouse gases, such as nitrous oxide (N2O) and methane (CH4). Despite the rich iron chemistry in zeolites, only a fraction of iron species that exhibit an open coordination sphere and possess the ability for electron transfer are responsible for activating reagents. In addition, the splitting of molecular oxygen is facilitated by bare iron cations embedded in zeolitic matrices. Mössbauer spectroscopy is the ideal tool for investigating the valency and geometry of iron species in zeolites because it leaves no iron forms silent and provides insights into in‐situ processes. This review is dedicated to the utilization of Mössbauer spectroscopy to elucidate the nature of the extra‐framework iron centers in ferrierite (FER), beta‐structured (*BEA), and ZSM‐5 zeolite (MFI) zeolites, which are active in N2O decomposition and CH4 oxidation through using the active oxygen derived from N2O and O2. In this work, a structured summary of the Mössbauer parameters established over the last two decades is presented, characterizing the specific iron active centers and intermediates formed upon iron's interaction with N2O/O2 and CH4. Additionally, the impact of preparation methods, iron loading, and the long‐term stability on iron speciation and its redox behavior under reaction conditions is discussed. Mössbauer spectroscopy is extensively employed in the characterization of iron‐containing materials. Here, we explore the application of Mössbauer spectroscopy to the identification of active iron centers located in extra‐framework positions in FER, *BEA, and MFI zeolites, which serve as catalysts for N2O decomposition and CH4 oxidation by active oxygen derived from N2O and O2.