Research ArticleMATERIALS SCIENCE

Dioxygen dissociation over man-made system at room temperature to form the active α-oxygen for methane oxidation

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Science Advances  13 May 2020:
Vol. 6, no. 20, eaaz9776
DOI: 10.1126/sciadv.aaz9776

Figures

  • Fig. 1 Optimized structures.

    (A) The two adjacent β sites of Fe-ferrierite 1 after molecular dynamics (MD) simulations. (B) The monodentate Fe OOmono…Fe complex 2 formed in the two adjacent β sites. (C) The bidentate Fe OObi…Fe complex 3 formed in the two adjacent β sites. (D) The transition state TS created in the two adjacent β sites. (E) The Fe═O O═Fe product 4 created in the two adjacent β sites. The distances are in angstroms. Silicon atoms are in gray, oxygen atoms in red, aluminum atoms in yellow, and iron atoms in blue. Schematic energy profile (in kilocalorie per mole). (F) The formation of the Fe═O O═Fe product.

  • Fig. 2 Mössbauer spectra and their fits of 57Fe-ferrierite.

    (A) Mössbauer spectra after an evacuation at 450°C for 3 hours. (B) An evacuation at 450°C for 3 hours, then an interaction with O2 (105 Pa) at room temperature for 40 min, and after that, a desorption of O2 at 200°C for 5 min. The curve in red represents the α-oxygens. (C) An evacuation at 450°C for 3 hours and then an interaction with O2 (105 Pa) at room temperature for 40 min, and subsequently, a desorption of O2 at 200°C for 5 min, and after that, an interaction with CH4 (105 Pa) at room temperature for 40 min, and subsequently, an evacuation of CH4 at 200°C for 5 min. The insets show the corresponding full-range spectra.

  • Fig. 3 FTIR spectra of Fe-ferrierite.

    (A) FTIR spectra after an evacuation at 450°C for 3 hours. The measured data correspond to the dots, while the gray curves represent the deconvoluted profiles. (B) An evacuation at 450°C for 3 hours and then an interaction with O2 (105 Pa) at room temperature for 40 min (black curve), and after that, a desorption of O2 at 200°C for 5 min (red curve). (C) An evacuation at 450°C for 3 hours and then an interaction with O2 (105 Pa) at room temperature for 40 min, and subsequently, a desorption of O2 at 200°C for 5 min, and after that, an interaction with CH4 (105 Pa) at room temperature for 40 min, and subsequently, an evacuation of CH4 at 200°C for 5 min.

  • Fig. 4 The mass spectrometry results for Fe-ferrierite.

    Time dependence of the intensity of the signals of ion currents reflecting the products of the oxidation of methane by the α-oxygen formed on Fe-ferrierite during the first oxidation cycle monitored by mass spectrometry (MS). The signal with m/z = 31 relates to methanol, that with m/z = 44 links with CO2, and that with m/z = 29 corresponds to methanol and other possible oxidation products (i.e., formaldehyde, formic acid, and dimethyl ether).

Tables

  • Table 1 Mössbauer parameters and spectral contributions of 57Fe-ferrierite.

    57Fe-FERIsomer shiftQuadrupole splittingRel.Fe species
    Fe/Al 0.04mm/smm/s%
    Evacuated*0.930.4633Fe(II)
    0.980.7240Fe(II)
    1.022.0627Fe(II)
    +O20.890.5110Fe(II)
    1.601.3218Fe(II)
    0.380.7872Fe(III)-O−●
    +O2/CH40.980.4939Fe(II)
    0.900.8331Fe(II)
    1.052.1430Fe(II)

    *An evacuation at 450°C for 3 hours.

    †An evacuation at 450°C for 3 hours, then an interaction with O2 at room temperature for 40 min, and after that, an O2 desorption at 200°C for 5 min.

    ‡An evacuation at 450°C for 3 hours, then an interaction with O2 at room temperature for 40 min, and consequently, a desorption of O2 at 200°C for 5 min, and after that, an interaction with CH4 at room temperature for 40 min, and subsequently, an evacuation of CH4 at 200°C for 5 min.

    • Table 2 Yields of methanol from the MS experiments.

      Yield of
      CH3OH [μmol/
      gcat]
      CH3OH/Fe
      [mol/mol]
      CH3OH/Feβ
      [mol/mol]
      First cycle750.440.63
      Second cycle520.300.44

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