Do synthetic Fe-zeolites mimic biological Fe-porphyrins in reactions with nitric oxide?

• Published in: Catalysis today Vol. 157; no. 1; pp. 223 - 230
• Main Authors: Rivallan, Mickaël, Bromley, Bryan, Kiwi-Minsker, Lioubov
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 17.11.2010; Elsevier
• Subjects: Alpha oxygen; Bent/linear nitrosyl; Catalysis; Chemistry; Exact sciences and technology; Fe(Porph); Fe–ZSM-5; General and physical chemistry; Ion-exchange; Nitric oxide; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolites: preparations and properties; Alpha oxygen; Fe–ZSM-5; Fe(Porph); Nitric oxide; Bent/linear nitrosyl; Modification; Oxygen; Nitrogen heterocycle; Active site; Thermodesorption; Transition metal; Decomposition; Iron; Fe―ZSM-5; Characterization; Geometry; Infrared spectrometry; Heterogeneous catalysis; Porphyrin; Models; Oxidation; Nitrogen protoxide; Structure
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2010.04.014

Iron containing ZSM-5 zeolites is extremely active in nitrous oxide decomposition. This reaction involves atomic oxygen species known as “alpha oxygen” on iron sites. Despite the multiple techniques devoted to its characterization, the active sites’ structure remains nevertheless unknown. Herein, these centers are quantified via surface titration by nitrous oxide followed by temperature programmed desorption and characterized via nitric oxide probe molecule followed by infrared spectroscopy. In this latter case, two mono-nitrosyl species differing in the bonds’ geometry are observed on the iron centers. Moreover, upon NO evacuation, the two corresponding IR bands suddenly transit to lower wavenumbers. A mirror trend is also reported in biology when NO interacts with iron porphyrins and explained in terms of linear to bent Fe–N–O modification. This structural change is reversible upon addition/evacuation of NO. In the present report, the same reversible nitrosyl transition is observed for Fe–ZSM-5. Based on the close analogies found, the active site's structure in Fe–ZSM-5 is built-up from the porphyrinatoiron(II) model.