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Carbon-free H2 production from ammonia triggered at room temperature with an acidic RuO2/γ-Al2O3 catalyst

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Science Advances  28 Apr 2017:
Vol. 3, no. 4, e1602747
DOI: 10.1126/sciadv.1602747
  • Fig. 1 Schematic of the catalytic cycle developed for oxidative decomposition of ammonia.
  • Fig. 2 Triggering tests over RuO2/γ-Al2O3.

    (A) Time dependence of formation rates of H2 and N2. (B) Temperatures at the inlet of the catalyst bed during oxidative decomposition of ammonia. (C) Distribution of the catalyst bed temperature measured at 300 s (see fig. S5). The catalysts were pretreated in pure He at 300°C and subsequently cooled to room temperature (~25°C) under He. The triggering tests were then carried out under quasi-adiabatic conditions (see fig. S4). A gaseous mixture (NH3/O2/He ratio, 150:37.5:20.8 ml min−1) was supplied at room temperature at a GHSV of 62.5 liters hour−1 gcat−1 (see fig. S3).

  • Fig. 3 Self-heating of catalysts upon the addition of ammonia.

    Time dependence of catalyst bed temperatures upon exposure of NH3/He to RuO2/γ-Al2O3 and RuO2/La2O3. The catalysts were pretreated in pure He at 300°C and subsequently cooled to room temperature under He. After this, a mixture of NH3/He (NH3/He ratio, 150:58.3 ml min−1) was supplied at room temperature to the catalysts.

  • Fig. 4 Relationship between heat evolution and amount of ammonia adsorbed.

    (A) Total heat evolution and amount of ammonia absorbed as a function of the adsorption-equilibrium pressure and (B) differential heat of ammonia adsorption as a function of total amount of ammonia adsorbed over RuO2/γ-Al2O3, γ-Al2O3, and RuO2/La2O3. (C) Image of ammonia adsorption on RuO2/γ-Al2O3. The catalysts were pretreated in pure He at 300°C and subsequently cooled to 50°C under He and kept under vacuum. Ammonia was then supplied at 50°C.

  • Fig. 5 Determination of the catalytic autoignition temperature.

    Changes in the catalyst bed temperatures for RuO2/γ-Al2O3 (A) and RuO2/La2O3 (B). After He pretreatment at 300°C, the catalyst bed temperatures were measured in a flow of NH3/He (NH3/He ratio, 150:20.8 ml min−1) and then with the addition of O2 (37.5 ml min−1) to the gas stream.

  • Fig. 6 Cycle tests over RuO2/γ-Al2O3.

    For the first cycle, the triggering test was carried out as described in Fig. 2. After 35 min, the reaction was terminated by substitution of the NH3/O2/He mixture with He, and the catalyst was cooled to room temperature. O2 was then briefly supplied over the catalyst, and an NH3/O2/He mixture (NH3/O2/He ratio, 150:37.5:20.8 ml min−1) with a GHSV of 62.5 liters hour−1 gcat−1 was supplied to the catalyst for the measurement (fig. S10). This purge-feed sequence was repeated three more times. The dotted line shows the calculated maximum theoretical percentage yield of hydrogen (that is, 67%), assuming a stoichiometric reaction between ammonia and O2 (Eq. 2).

  • Fig. 7 Results for long-term testing over RuO2/γ-Al2O3.

    The triggering test was carried out as described in Fig. 2.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1602747/DC1

    Procedures for characterizing the catalysts

    fig. S1. Conversions and yields for oxidative decomposition of ammonia (Eq. 2) calculated from thermodynamics with HSC Chemistry 6.1.

    fig. S2. Characterizations of RuO2/γ-Al2O3.

    fig. S3. Typical experimental procedure for triggering tests using heat produced by adsorption of ammonia on the catalyst.

    fig. S4. Schematic of the quasi-adiabatic reactor with a quadrupole mass spectrometer (Q-MS) and gas chromatograph (GC).

    fig. S5. Experimental setup for observing the temperature distribution of the catalyst bed.

    fig. S6. Trends of MS peak intensities during triggering tests over RuO2/γ-Al2O3 (A) and bare γ-Al2O3 (B).

    fig. S7. Triggering tests over RuO2/γ-Al2O3 with three GHSVs.

    fig. S8. Distribution of catalyst bed temperature measured at 300 s during triggering tests over RuO2/γ-Al2O3 with three GHSVs.

    fig. S9. NH3-TPD profiles of RuO2/γ-Al2O3 (solid lines) and bare γ-Al2O3 (dashed lines).

    fig. S10. Experimental procedure used for five cycles of testing.

    table S1. Conversions of ammonia and oxygen and yields of hydrogen during triggering tests over RuO2/γ-Al2O3 at three GHSVs.

    table S2. Proportions of converted NH3 and O2 and percentage yields of hydrogen during triggering tests over RuO2/γ-Al2O3 with various NH3/O2 molar ratios in the feed gas.

    table S3. Physicochemical properties of the catalysts.

    table S4. Molar ratio of Ru/Al in RuO2/γ-Al2O3 before testing (untreated), after five cycles of testing, and after long-term testing (100 hours).

    Reference (39)

  • Supplementary Materials

    This PDF file includes:

    • Procedures for characterizing the catalysts
    • fig. S1. Conversions and yields for oxidative decomposition of ammonia (Eq. 2) calculated from thermodynamics with HSC Chemistry 6.1.
    • fig. S2. Characterizations of RuO2/γ-Al2O3.
    • fig. S3. Typical experimental procedure for triggering tests using heat produced by adsorption of ammonia on the catalyst.
    • fig. S4. Schematic of the quasi-adiabatic reactor with a quadrupole mass spectrometer (Q-MS) and gas chromatograph (GC).
    • fig. S5. Experimental setup for observing the temperature distribution of the catalyst bed.
    • fig. S6. Trends of MS peak intensities during triggering tests over RuO2/γ-Al2O3 (A) and bare γ-Al2O3 (B).
    • fig. S7. Triggering tests over RuO2/γ-Al2O3 with three GHSVs.
    • fig. S8. Distribution of catalyst bed temperature measured at 300 s during triggering tests over RuO2/γ-Al2O3 with three GHSVs.
    • fig. S9. NH3-TPD profiles of RuO2/γ-Al2O3 (solid lines) and bare γ-Al2O3 (dashed lines).
    • fig. S10. Experimental procedure used for five cycles of testing.
    • table S1. Conversions of ammonia and oxygen and yields of hydrogen during triggering tests over RuO2/γ-Al2O3 at three GHSVs.
    • table S2. Proportions of converted NH3 and O2 and percentage yields of hydrogen during triggering tests over RuO2/γ-Al2O3 with various NH3/O2 molar ratios in the feed gas.
    • table S3. Physicochemical properties of the catalysts.
    • table S4. Molar ratio of Ru/Al in RuO2/γ-Al2O3 before testing (untreated), after five cycles of testing, and after long-term testing (100 hours).
    • Reference (39)

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