Research ArticleCHEMICAL PHYSICS

Disentangling the size-dependent geometric and electronic effects of palladium nanocatalysts beyond selectivity

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Science Advances  18 Jan 2019:
Vol. 5, no. 1, eaat6413
DOI: 10.1126/sciadv.aat6413
  • Fig. 1 Catalytic performance of Pd/Al2O3 catalysts with different particle sizes in aerobic oxidation of benzyl alcohol.

    (A) Benzaldehyde and toluene selectivity as a function of Pd particle size at 50% benzyl alcohol conversion. (B) TOFs as a function of Pd particle size. The inset in (B) shows the specific rates as a function of Pd particle size. The selectivity and TOF of the 4.2-nm Pd/Al2O3 catalyst with 10 cycles of ALD alumina overcoat (10Al2O3-Pd) under the same reaction conditions were also presented in (A) and (B), respectively, for comparison (star). Reaction conditions: normalized Pd content, 1.6 μmol Pd; substrate, 48 mmol benzyl alcohol; reaction temperature, 120°C; O2 flow rate, 15 ml/min.

  • Fig. 2 The electronic and geometric properties of Pd/Al2O3 catalysts on Pd particle size.

    (A) In situ XPS spectra of the Pd/Al2O3 catalysts with various particle sizes in the Pd 3d region. a.u., arbitrary units. (B) The Pd 3d5/2 binding energy shift compared with the 19.1-nm Pd NP sample as a function of Pd particle size, and the calculated ratios of Pd HCSs to LCSs for the Pd/Al2O3 catalysts with various particle sizes based on the cubooctahedral cluster model, as illustrated by the inset in (B).

  • Fig. 3 Structural characterization of Al2O3- and FeOx-overcoated 4.2-nm Pd/Al2O3 samples and their catalytic performances.

    DRIFT spectra of CO chemisorption on the (A) ALD Al2O3- and (B) FeOx-overcoated Pd/Al2O3 samples at the CO saturated coverage. The insets illustrate selective blocking of the LCSs (A) or HCSs (B) of Pd NPs with Al2O3 and FeOx ALD overcoat, respectively. (C) Tuned selectivity to benzaldehyde and toluene in benzyl alcohol oxidation on Pd/Al2O3 by oxide overcoats as a function of exposed Pd HCS-to-LCS ratio, measured at 50% benzyl alcohol conversion; the lines in (C) are only for guiding the eyes. Reaction conditions: normalized Pd content, 1.6 μmol Pd; substrate, 48 mmol benzyl alcohol; reaction temperature, 120°C; O2 flow rate, 15 ml/min.

  • Fig. 4 Theoretical calculations of Pd-catalyzed benzyl alcohol oxidation.

    (A) Calculated energy barriers in the oxidative dehydrogenation from benzyl alcohol to benzyloxy and OH and from benzyloxy to benzaldehyde and hydrogen on Pd(111), Pd(211), and Pd55. (B) Calculated energy barriers for competing hydrogenation of benzyl and hydroxyl to toluene and water on Pd(111), Pd(211), and Pd55. (C) Relative binding energies of benzyl alcohol and benzyl on Pd55, Pd147, and Pd309 with respect to Pd(211) surface, as well as calculated charge transfer toward these species and corresponding work function. The absolute binding energies of (C6H5)CH2OH and (C6H5)CH2 on Pd(211) are −2.05 and −2.51 eV, respectively (see fig. S19). (D) Charge density difference upon adsorption of benzyl on Pd55 and Pd(211). The blue balls are Pd atoms, while the areas of cyan and yellow contours represent the depletion and accumulation of electrons in a unit of 0.001e/Å3, respectively.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/1/eaat6413/DC1

    Supplementary Text

    Fig. S1. Morphologies of Pd/Al2O3 catalysts with various particle sizes.

    Fig. S2. The corresponding Pd size distributions in the Pd/Al2O3 catalysts.

    Fig. S3. The apparent activation energies for benzaldehyde and toluene formation.

    Fig. S4. A representative TEM image of the 10Al2O3-Pd catalyst.

    Fig. S5. A representative STEM image of the 8FeOx-Pd catalyst.

    Fig. S6. The Pd particle size distributions of uncoated and oxide-coated samples.

    Fig. S7. In situ XPS spectra of Pd/Al2O3, 10Al2O3-Pd, and 8FeOx-Pd samples in the Pd 3d region.

    Fig. S8. Semiquantitative analysis of the DRIFT spectra.

    Fig. S9. The ratios of exposed Pd HCSs to LCSs on oxide-coated and uncoated Pd/Al2O3 samples determined by semiquantitative analysis of the DRIFT CO chemisorption spectra.

    Fig. S10. Catalytic performance of 4.2-nm Pd/Al2O3 catalysts with different cycles of alumina and FeOx overcoating in aerobic oxidation of benzyl alcohol at 120°C.

    Fig. S11. Catalytic performance of 4.2-nm Pd/Al2O3 catalysts with different cycles of alumina overcoating in aerobic oxidation of benzyl alcohol at 120°C.

    Fig. S12. Catalytic performance of 4.2-nm Pd/Al2O3 and 10Al2O3-Pd catalysts in aerobic oxidation of benzyl alcohol at different temperatures.

    Fig. S13. Catalytic performance of 4.2-nm Pd/Al2O3 and 10Al2O3-Pd catalysts in aerobic oxidation of benzyl alcohol at 90°C.

    Fig. S14. Catalytic performance of 4.2-nm Pd/Al2O3 and 10Al2O3-Pd catalysts in aerobic oxidation of benzyl alcohol at 140°C.

    Fig. S15. Structural characterization of Al2O3- and FeOx-overcoated 5.1-nm Pd/Al2O3 samples and their catalytic performances.

    Fig. S16. Morphology of the 2.9-nm Pd/C catalyst.

    Fig. S17. Catalytic performance of the 2.9-nm Pd/C, 10Al2O3-Pd/C, and 8FeOx-Pd/C catalysts in aerobic oxidation of benzyl alcohol at 120°C.

    Fig. S18. Recycling stability of the 10Al2O3-Pd catalyst.

    Fig. S19. Optimized geometries and calculated binding energies of benzyl alcohol and its derived key intermediates on Pd surfaces.

    Fig. S20. Optimized geometries and calculated binding energies of O2, O, H, OH, and H2O intermediates on Pd surfaces with respect to the corresponding species in the gas phase.

    Fig. S21. The side views of optimized geometries of benzyl alcohol and its derived key intermediates on Pd surfaces.

    Fig. S22. The transition states of elementary steps involved in benzyl alcohol oxidation on Pd(111).

    Fig. S23. The transition states of elementary steps involved in benzyl alcohol oxidation on Pd(211).

    Fig. S24. Energy profiles of the direct and oxidative dehydrogenation paths on Pd surfaces.

    Fig. S25. Energy profiles of the hydrogenolysis path to toluene formation on Pd surfaces.

    Fig. S26. Energy profiles of C–O scission of (C6H5)CH2OH*, (C6H5)CHOH*, and (C6H5)CH2O* on Pd surfaces.

    Fig. S27. Models of freestanding Pd55, Pd147, and Pd309 clusters.

    Fig. S28. The optimized most stable geometries of (C6H5)CH2OH*, (C6H5)CH2*, and OH* on freestanding Pd55, Pd147, and Pd309 clusters.

    Fig. S29. Comparison of the side view of charge density difference upon adsorption of benzyl on Pd55, Pd147, Pd309, and Pd(211) surfaces.

    Fig. S30. Comparison of the top view of charge density difference upon adsorption of benzyl on Pd55, Pd147, Pd309, and Pd(211) surfaces.

    Fig. S31. Optimized transition state structures of the key steps involved in benzaldehyde and toluene formations on Pd55 cluster.

    Fig. S32. Energy profiles of the oxidative dehydrogenation and hydrogenolysis paths on Pd55 cluster.

    Table S1. Conditions for synthesis of Pd/Al2O3 samples with various Pd particle sizes using the WI method.

    Table S2. Calculated activation barriers (Ea) and reaction energies (Er) of elementary steps in oxidation of benzyl alcohol on Pd(111) and Pd(211) surfaces.

    Table S3. Pd dispersion determined by CO pulse chemisorption for various Pd catalysts.

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • Fig. S1. Morphologies of Pd/Al2O3 catalysts with various particle sizes.
    • Fig. S2. The corresponding Pd size distributions in the Pd/Al2O3 catalysts.
    • Fig. S3. The apparent activation energies for benzaldehyde and toluene formation.
    • Fig. S4. A representative TEM image of the 10Al2O3-Pd catalyst.
    • Fig. S5. A representative STEM image of the 8FeOx-Pd catalyst.
    • Fig. S6. The Pd particle size distributions of uncoated and oxide-coated samples.
    • Fig. S7. In situ XPS spectra of Pd/Al2O3, 10Al2O3-Pd, and 8FeOx-Pd samples in the Pd 3d region.
    • Fig. S8. Semiquantitative analysis of the DRIFT spectra.
    • Fig. S9. The ratios of exposed Pd HCSs to LCSs on oxide-coated and uncoated Pd/Al2O3 samples determined by semiquantitative analysis of the DRIFT CO chemisorption spectra.
    • Fig. S10. Catalytic performance of 4.2-nm Pd/Al2O3 catalysts with different cycles of alumina and FeOx overcoating in aerobic oxidation of benzyl alcohol at 120°C.
    • Fig. S11. Catalytic performance of 4.2-nm Pd/Al2O3 catalysts with different cycles of alumina overcoating in aerobic oxidation of benzyl alcohol at 120°C.
    • Fig. S12. Catalytic performance of 4.2-nm Pd/Al2O3 and 10Al2O3-Pd catalysts in aerobic oxidation of benzyl alcohol at different temperatures.
    • Fig. S13. Catalytic performance of 4.2-nm Pd/Al2O3 and 10Al2O3-Pd catalysts in aerobic oxidation of benzyl alcohol at 90°C.
    • Fig. S14. Catalytic performance of 4.2-nm Pd/Al2O3 and 10Al2O3-Pd catalysts in aerobic oxidation of benzyl alcohol at 140°C.
    • Fig. S15. Structural characterization of Al2O3- and FeOx-overcoated 5.1-nm Pd/Al2O3 samples and their catalytic performances.
    • Fig. S16. Morphology of the 2.9-nm Pd/C catalyst.
    • Fig. S17. Catalytic performance of the 2.9-nm Pd/C, 10Al2O3-Pd/C, and 8FeOx-Pd/C catalysts in aerobic oxidation of benzyl alcohol at 120°C.
    • Fig. S18. Recycling stability of the 10Al2O3-Pd catalyst.
    • Fig. S19. Optimized geometries and calculated binding energies of benzyl alcohol and its derived key intermediates on Pd surfaces.
    • Fig. S20. Optimized geometries and calculated binding energies of O2, O, H, OH, and H2O intermediates on Pd surfaces with respect to the corresponding species in the gas phase.
    • Fig. S21. The side views of optimized geometries of benzyl alcohol and its derived key intermediates on Pd surfaces.
    • Fig. S22. The transition states of elementary steps involved in benzyl alcohol oxidation on Pd(111).
    • Fig. S23. The transition states of elementary steps involved in benzyl alcohol oxidation on Pd(211).
    • Fig. S24. Energy profiles of the direct and oxidative dehydrogenation paths on Pd surfaces.
    • Fig. S25. Energy profiles of the hydrogenolysis path to toluene formation on Pd surfaces.
    • Fig. S26. Energy profiles of C–O scission of (C6H5)CH2OH*, (C6H5)CHOH*, and (C6H5)CH2O* on Pd surfaces.
    • Fig. S27. Models of freestanding Pd55, Pd147, and Pd309 clusters.
    • Fig. S28. The optimized most stable geometries of (C6H5)CH2OH*, (C6H5)CH2*, and OH* on freestanding Pd55, Pd147, and Pd309 clusters.
    • Fig. S29. Comparison of the side view of charge density difference upon adsorption of benzyl on Pd55, Pd147, Pd309, and Pd(211) surfaces.
    • Fig. S30. Comparison of the top view of charge density difference upon adsorption of benzyl on Pd55, Pd147, Pd309, and Pd(211) surfaces.
    • Fig. S31. Optimized transition state structures of the key steps involved in benzaldehyde and toluene formations on Pd55 cluster.
    • Fig. S32. Energy profiles of the oxidative dehydrogenation and hydrogenolysis paths on Pd55 cluster.
    • Table S1. Conditions for synthesis of Pd/Al2O3 samples with various Pd particle sizes using the WI method.
    • Table S2. Calculated activation barriers (Ea) and reaction energies (Er) of elementary steps in oxidation of benzyl alcohol on Pd(111) and Pd(211) surfaces.
    • Table S3. Pd dispersion determined by CO pulse chemisorption for various Pd catalysts.

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