Evolution of Active Oxygen Species Originating from O2 Cleavage over Fe-FER for Application in Methane Oxidation

Abstract

Here, we show a spectroscopic study of the formation and oxidation properties of α-oxygen originating from O2 dissociation over binuclear Fe(II) structure in Fe-ferrierite. The investigation of its formation, stability, and methane oxidation properties toward methanol formation at elevated temperatures was confirmed by in situ FTIR spectroscopy and mass spectrometry. For a deeper insight into the redox properties of Fe centers embedded in ferrierite, Mössbauer and X-ray adsorption spectroscopies were used as complementary methods. In situ FTIR spectroscopy and activity test results recorded at elevated temperatures convenient for potential industrial applications (through-flow reactor, 220 °C) showed that binuclear Fe(II) centers in FER can split O2 and form stable species [Fe(IV)=O]2+ active in three consecutive cycles in methane to methanol oxidation. Those results were confirmed by changes in the values of hyperfine parameters of iron species in ferrierite in Mössbauer spectra and by changes in the Fe K-edge XAS spectrum recorded under redox conditions.