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Chemical imaging of Fischer-Tropsch catalysts under operating conditions

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Science Advances  17 Mar 2017:
Vol. 3, no. 3, e1602838
DOI: 10.1126/sciadv.1602838
  • Fig. 1 Conventional catalyst precursor structure.

    (Top) XRF-CT reconstructions showing elemental distributions for the conventional catalytic precursor. Green, Ti; blue, Co; orange, Re. Absorption-CT reconstruction (gray) also shows the capillary wall surrounding the particles. (Middle) XRD-CT reconstructions of the conventional catalyst revealing the phases present. (Bottom) Average crystallite size per pixel for each phase identified. Each pixel is 5 μm × 5 μm. Gas flow was 6 ml min−1 He at 25°C.

  • Fig. 2 Conventional catalyst structure after reduction.

    (Top) XRF-CT reconstructions showing elemental distributions for the conventional catalyst after the reduction step. Green, Ti; blue, Co; orange, Re. Absorption-CT reconstruction (gray) also shows the capillary wall surrounding the particles. (Middle) XRD-CT reconstructions of the conventional catalyst revealing the phases present. (Bottom) Average crystallite size per pixel for each phase identified. Each pixel is 5 μm × 5 μm. Gas flow was 6 ml min−1 5% H2/He at 400°C.

  • Fig. 3 Conventional catalyst structure during FTS.

    (Top) XRF-CT reconstructions showing elemental distributions for the conventional catalyst during FTS at 2-bar pressure. Green, Ti; blue, Co; orange, Re. Absorption-CT reconstruction (gray) also shows the capillary wall surrounding the particles. (Middle) XRD-CT reconstructions of the conventional catalyst revealing the phases present. (Bottom) Average crystallite size per pixel for each phase identified. Each pixel is 5 μm × 5 μm. Gas flow was 4 ml min−1 5% H2/He and 2 ml min−1 5% CO/He at 200°C (H2/CO 2:1 and 95% inerts).

  • Fig. 4 Offline mass spectrometry.

    ■ □, Offline CO conversion; ● ○, CH4 selectivity; C5+ ▲ △, selectivity. Conventional catalyst (closed points), inverse catalyst (open points). T = 205°C, P = 20 bar, H2/CO = 2;1, 5% N2, gas hourly space velocity = 3100 hour−1. Tabulated values are shown in table S4.

  • Fig. 5 Simulation of diffraction patterns.

    (Left) Co crystal structures used for XRD simulations: Cubic (fcc) with ABC stacking, intergrown with fully random stacking, and hexagonal (hcp) with ABAB layer sequence. (Right) Exemplar fit of the XRD pattern generated from cluster analysis of inverse catalyst after reduction using DISCUS. Black points, experimental pattern; red, fitted pattern; blue, fit to cubic phase; green, fit to intergrown phase; gray, difference curve.

  • Table 1 Fitted XRD crystallite sizes and dispersion for Ti and Co phases.

    The error in the average sizes is ±0.5 nm.

    Sample and conditionPhases and average crystallite sizes (nm)Dispersion
    TiO2Co3O4CoOCubic CoIntergrown CoCubic Co dispersionIntergrown Co dispersion*
    ConventionalCalcined3.010.06.0
    Reduced3.06.93.313.929.1
    FTS (2 bar)3.06.09.56.510.114.8
    InverseCalcined12.57.0
    Reduced9.03.010.732
    FTS (2 bar)8.53.011.332

    *Co dispersion was estimated using the formula D = 96/d, where D (%) is Co dispersion and d (nm) is Co particle size (62), assuming uniform spheres of Co and a site density of 15.2 atoms/nm2. If the intergrown and cubic domains are part of a larger particle, then the average particle size will be somewhat larger than that reported, and consequently, the dispersion will be lower.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1602838/DC1

      Supplementary Text

      fig. S1. Schematic of the experimental setup including exemplar XRF spectrum and XRD pattern.

      fig. S2. TPR results.

      fig. S3. Deviation in lattice parameter (±1%) from standard value (white) for conventional and inverse catalyst for room temperature measurements of the calcined catalyst.

      fig. S4. Summed XRD patterns from each XRD-CT measurement.

      fig. S5A. Inverse catalyst precursor structure.

      fig. S5B. Inverse catalyst structure after reduction.

      fig. S5C. Inverse catalyst structure during FTS at 2 bar.

      fig. S6. Diffraction cluster analysis.

      fig. S7. Deviation in lattice parameter (±1%) from standard value (white) for conventional catalyst after reduction (top), and during FTS at 2 bar (middle) and 4 bar (bottom).

      fig. S8. Deviation in lattice parameter (±1%) from standard value (white) for inverse catalyst after reduction (top), and during FTS at 2 bar (middle) and 4 bar (bottom).

      fig. S9. Change in summed XRD patterns for the conventional catalyst between reduction and FTS (2 bar).

      fig. S10A. Conventional catalyst mass spectrometry traces for C1+-C6+.

      fig. S10B. Inverse catalyst mass spectrometry traces for C1+-C6+.

      fig. S11. Conventional catalyst structure during FTS at 4 bar.

      fig. S12. Inverse catalyst structure during FTS at 4 bar.

      table S1. BET (surface area) and BJH (pore volume and size) results.

      table S2. Results of phase identification simulations of active reduced catalysts.

      table S3. Results of phase identification simulations of catalysts under 2-bar FTS conditions.

      table S4. Activity and selectivity of the catalysts, offline testing corresponding to Fig. 4.

      References (63, 64)

    • Supplementary Materials

      This PDF file includes:

      • Supplementary Text
      • fig. S1. Schematic of the experimental setup including exemplar XRF spectrum and XRD pattern.
      • fig. S2. TPR results.
      • fig. S3. Deviation in lattice parameter (±1%) from standard value (white) for conventional and inverse catalyst for room temperature measurements of the calcined catalyst.
      • fig. S4. Summed XRD patterns from each XRD-CT measurement.
      • fig. S5A. Inverse catalyst precursor structure.
      • fig. S5B. Inverse catalyst structure after reduction.
      • fig. S5C. Inverse catalyst structure during FTS at 2 bar.
      • fig. S6. Diffraction cluster analysis.
      • fig. S7. Deviation in lattice parameter (±1%) from standard value (white) for conventional catalyst after reduction (top), and during FTS at 2 bar (middle) and 4 bar (bottom).
      • fig. S8. Deviation in lattice parameter (±1%) from standard value (white) for inverse catalyst after reduction (top), and during FTS at 2 bar (middle) and 4 bar (bottom).
      • fig. S9. Change in summed XRD patterns for the conventional catalyst between reduction and FTS (2 bar).
      • fig. S10A. Conventional catalyst mass spectrometry traces for C1+-C6+.
      • fig. S10B. Inverse catalyst mass spectrometry traces for C1+-C6+.
      • fig. S11. Conventional catalyst structure during FTS at 4 bar.
      • fig. S12. Inverse catalyst structure during FTS at 4 bar.
      • table S1. BET (surface area) and BJH (pore volume and size) results.
      • table S2. Results of phase identification simulations of active reduced catalysts.
      • table S3. Results of phase identification simulations of catalysts under 2-bar FTS conditions.
      • table S4. Activity and selectivity of the catalysts, offline testing corresponding to Fig. 4.
      • References (63, 64)

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