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MnTiO3-driven low-temperature oxidative coupling of methane over TiO2-doped Mn2O3-Na2WO4/SiO2 catalyst

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Science Advances  09 Jun 2017:
Vol. 3, no. 6, e1603180
DOI: 10.1126/sciadv.1603180
  • Fig. 1 The MnTiO3-governed OCM performance of the TiO2-doped Mn2O3-Na2WO4/SiO2 catalysts.

    (A) CH4 conversion and C2-C3 selectivity over the Ti-MWW–, TS-1–, and SiO2-supported Mn2O3-Na2WO4 catalysts. (B) XRD patterns of the Mn2O3-Na2WO4/Ti-MWW, Mn2O3-Na2WO4/TS-1, and Mn2O3-Na2WO4/SiO2 catalysts, with (C) the magnified part of 2θ from 31° to 37°. a.u., arbitrary units; α-Crist., α-cristobalite. (D) CH4 conversion and C2-C3 selectivity and (E) XRD patterns as well as (F) the magnified part of 2θ from 31° to 37° of the Mn2O3-Na2WO4/Ti-MWW catalysts with different Si:Ti molar ratio in Ti-MWW zeolites after directly running at 720°C. (G and H) Raman spectra of the Ti-MWW–, TS-1–, and SiO2-supported Mn2O3-Na2WO4 catalysts. Reaction conditions: GHSV of 8000 ml gcat.−1 hour−1 of a feed of 50% CH4 in air. C3 selectivity was 3 to 5%, 2 to 3%, and 0 to 2% for all catalysts at a C2-C3 total selectivity above 60%, between 40 and 60%, and below 40%, respectively.

  • Fig. 2 The temperature-dependent evolution of phase structures and surface states for the Ti-MWW– and SiO2-supported Mn2O3-Na2WO4 catalysts in O2 or CH4 at 720° to 800°C.

    (A to C) XRD patterns. The Mn3+ fractions evolving at (D) 800°C, (E) 760°C, and (F) 720°C. (G to I) Raman spectra. The Ti-MWW–supported catalyst reduced in CH4 at 800°C for 0.5 hour exhibits dominant MnTiO3 signal. After subsequent oxidation in O2 stream for 1 min at 800°C, 2 min at 760°C, and 4 min at 720°C, the MnTiO3 signal disappears, whereas the TiO2 appears, and is reformed in CH4 stream for 9 min at 800°C, 15 min at 760°C, and 30 min at 720°C. The SiO2-supported catalyst reduced in CH4 at 800°C for 0.5 hour exhibits a dominant MnWO4 signal. After subsequent oxidation in O2 stream for 3 min at 800°C, 15 min at 760°C, and 30 min at 720°C, the MnWO4 signal disappears, whereas the Mn2O3 appears, and can be reformed in CH4 stream for 15 min at 800°C, 35 min at 760°C, and 60 min at 720°C. The detailed calculations of the Mn3+ fractions are given in the Supplementary Materials.

  • Fig. 3 The Mn2+-to-Mn3+ transition rate and proposed catalytic recycle for OCM process.

    (A) Temperature-dependent transition rate of Mn2+ to Mn3+ correlated to CH4 conversion. (B) The Mn2O3-Na2WO4/Ti-MWW and Mn2O3-Na2WO4/SiO2 catalysts and the proposed catalytic cycles of Mn2O3-Na2WO4 and MnTiO3-Na2WO4 combinations. Detailed calculations of the transition rate are given in the Supplementary Materials.

  • Fig. 4 The OCM performance and XRD/Raman results of the 6.2Mn2O3-6.3TiO2-10Na2WO4/SiO2 catalyst.

    (A) Temperature-dependent CH4 conversion and C2-C3 selectivity. (B) XRD pattern and (C) Raman spectrum of this catalyst. (D) CH4 conversion and C2-C3 selectivity along with the time on stream at 720°C. Reaction conditions: GHSV of 8000 ml gcat.−1 hour−1 of a feed of 50% CH4 in air. The C3 selectivity was 3 to 5%, 2 to 3%, and 0 to 2% for all catalysts at a C2-C3 total selectivity above 60%, between 40 and 60%, and below 40%, respectively.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/6/e1603180/DC1

    Supplementary Text

    fig. S1. CH4 conversion and C2-C3 selectivity for the pure supports and the supported Mn2O3-Na2WO4 catalysts.

    fig. S2. SEM and EDX mapping images.

    fig. S3. XRD patterns and testing results of the 2.7Mn2O3-5.0Na2WO4/Ti-MWW and 2.7Mn2O3-5.0Na2WO4/TS-1 catalysts under different reaction conditions.

    fig. S4. XRD patterns and testing results for various samples with different Si:Ti molar ratio (or Ti content).

    fig. S5. XPS spectra of various samples.

    fig. S6. Raman spectra of various samples.

    fig. S7. Testing results of the catalysts with different active components.

    fig. S8. Ea calculations.

    fig. S9. Testing results of the catalysts with different active components prepared by the grinding method.

    fig. S10. H2-TPR profiles and XRD patterns.

    fig. S11. Effects of Mn2O3 plus TiO2, and Na2WO4 loadings on the OCM performance for the Mn2O3-TiO2-Na2WO4/SiO2 catalyst.

    fig. S12. Stability testing of the 6.2Mn2O3-6.3TiO2-10Na2WO4/SiO2 catalyst.

    fig. S13. Testing results and XRD patterns for the 6.2Mn2O3-6.3TiO2-10Na2WO4/SiO2 catalyst under different reaction conditions.

    table S1. Detailed treatment history of some catalysts for XRD and Raman measurements.

    table S2. Specific surface areas and real contents of Mn, W, Na, and Ti of all used catalysts.

    table S3. Surface contents of W, Mn, Na, Ti, Si, O, and C measured by XPS for the used catalysts.

    table S4. CH4 conversion and C2-C3 selectivity over representative catalysts.

    References (3849)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. CH4 conversion and C2-C3 selectivity for the pure supports and the supported Mn2O3-Na2WO4 catalysts.
    • fig. S2. SEM and EDX mapping images.
    • fig. S3. XRD patterns and testing results of the 2.7Mn2O3-5.0Na2WO4/Ti-MWW and 2.7Mn2O3-5.0Na2WO4/TS-1 catalysts under different reaction conditions.
    • fig. S4. XRD patterns and testing results for various samples with different Si:Ti molar ratio (or Ti content).
    • fig. S5. XPS spectra of various samples.
    • fig. S6. Raman spectra of various samples.
    • fig. S7. Testing results of the catalysts with different active components.
    • fig. S8. Ea calculations.
    • fig. S9. Testing results of the catalysts with different active components prepared by the grinding method.
    • fig. S10. H2-TPR profiles and XRD patterns.
    • fig. S11. Effects of Mn2O3 plus TiO2, and Na2WO4 loadings on the OCM performance for the Mn2O3-TiO2-Na2WO4/SiO2 catalyst.
    • fig. S12. Stability testing of the 6.2Mn2O3-6.3TiO2-10Na2WO4/SiO2 catalyst.
    • fig. S13. Testing results and XRD patterns for the 6.2Mn2O3-6.3TiO2-10Na2WO4/SiO2 catalyst under different reaction conditions.
    • table S1. Detailed treatment history of some catalysts for XRD and Raman measurements.
    • table S2. Specific surface areas and real contents of Mn, W, Na, and Ti of all used catalysts.
    • table S3. Surface contents of W, Mn, Na, Ti, Si, O, and C measured by XPS for the used catalysts.
    • table S4. CH4 conversion and C2-C3 selectivity over representative catalysts.
    • References (38–49)

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