Iron Nitrosyl Species in Fe-FER: A Complementary Mössbauer and FTIR Spectroscopy Study

Abstract

FTIR spectroscopy was applied to the investigation of the nitrosyl complexes formed with the extra-framework iron species in Fe-ferrierite (Fe-FER). To clarify the loading effect on the nature of the species formed, six ferrierites with Fe loadings varying between 0 and 3.7 wt % were prepared via ionic exchange and investigated. A Fe/SiO2 and a Fe-FER sample containing iron oxide were also studied for comparison purposes. Adsorption of NO on Fe-FER (containing no iron oxide species) gives different nitrosyl species, and different iron sites can be evidenced depending on the iron concentration. The bands are assigned to mononitrosyl on iron whose oxidation state is determined to be +2 thanks to Mössbauer spectroscopy. In particular, one specific Fe2+ cation (typical of a highly loaded sample) appears to be easily converted to Fe3+ upon oxygen treatment, which makes these sites excellent candidates for catalytically active redox sites.