The interaction of O2 with Fe supported on zeolite MFI has been investigated by the in situ UV Raman technique. Previously, the formation of adsorbed superoxide ions, O2- on the Fe/MFI prepared by sublimation of FeCl3 vapor onto HMFI, was identified by ESR at 77 K. In situ Raman data indicate that adsorbed peroxideions, O22-, are formed on the same catalysts with Fe/Al = 1 even at 300 K. A band at 730 cm-1, which was found to be sensitive to the partial pressure of O2, is tentatively assigned to the stretching vibration of peroxide ions. With the 18O2 isotope, a red shift of 32 cm-1 was observed for the 730 cm-1 band. Raman features of other catalyst samples show that the binuclear iron sites in the Fe/MFI are essential for the formation of peroxide ions. As proposed before, the same bridging sites between two Fe ions, that are occupied by O2- in the calcined catalyst, are also able to adsorb di-oxygen complexes.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry