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Molecular ligand modulation of palladium nanocatalysts for highly efficient and robust heterogeneous oxidation of cyclohexenone to phenol

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Science Advances  06 Jan 2017:
Vol. 3, no. 1, e1600615
DOI: 10.1126/sciadv.1600615
  • Fig. 1 Reaction pathway of Pd-catalyzed aerobic dehydrogenative oxidation of cyclohexenone to phenol.

    Ln represents the various β-substituted butyric acid ligands. HX represents the acids added to the reaction.

  • Fig. 2 Comparison of TON of heterogeneous nanoparticle catalysts with homogeneous molecular catalysts.

    TON of time-dependent reaction catalyzed by HB-Pd/C (red line) and Pd(TFA)2 (black line) with different substrate/catalyst ratios of (A) 100:3, (B) 1000:3, and (C) 10,000:3.

  • Fig. 3 TEM morphology and size distribution of HB-Pd/C, AB-Pd/C, CB-Pd/C, and commercial Pd/C.

    TEM morphology of (A) as-synthesized HB-Pd/C, (B) as-synthesized AB-Pd/C, (C) as-synthesized CB-Pd/C, (D) commercial Pd/C, (E) HB-Pd/C after 24-hour reaction, (F) AB-Pd/C after 24-hour reaction, (G) CB-Pd/C after 24-hour reaction, and (H) commercial Pd/C after 24-hour reaction. Scale bars, 40 nm. Inset histograms represent the size distribution of the corresponding samples.

  • Fig. 4 Time-dependent reaction profiles of 3-methylcyclohexenone dehydrogenative oxidation.

    The black and red lines represent the reaction profiles catalyzed by the fresh and reharvested catalysts: (A) HB-Pd/C, (B) AB-Pd/C, (C) CB-Pd/C, and (D) commercial Pd/C.

  • Table 1 The TON of heterogeneous catalyst HB-Pd/C and homogeneous catalyst Pd(TFA)2 under different reaction conditions.

    Under a low turnover condition, the substrate/catalyst ratio is 100:3; under a high turnover condition, the substrate/catalyst ratio is 1000:3; and under an ultrahigh turnover condition, the substrate/catalyst ratio is 10,000:3.

    EntryCatalystLow turnoverHigh turnoverUltrahigh turnover
    1HB-Pd/C31314>3000 (linear)
    2Pd(TFA)22028
  • Table 2 The yield of various heterogeneous catalysts mediated for 3-methylcyclohexenone dehydrogenative oxidation.

    The reactions were carried out in 10 ml of dimethyl sulfoxide (DMSO) solutions containing 1 mmol of 3-methylcyclohexenone, 0.03 mmol of Pd-equivalent catalysts, and 1.2 mmol of TFA under 1 atm of oxygen at 100°C for 24 hours.

    EntryCatalystFirst-cycle yield (%)Second-cycle yield (%)
    1HB-Pd/C9383
    2AB-Pd/C7424
    3CB-Pd/C5748
    4Commercial Pd/C67<1
  • Table 3 Zeta potential measurements on Pd nanoparticles before and after dispersing into a TFA/DMSO reaction solution.
    EntryCatalystZeta potential (mV)
    (as prepared)
    Zeta potential (mV)
    (after dispersing into
    reaction solution)
    1HB-Pd−23.2−2.79
    2CB-Pd−21.6−3.76
    3AB-Pd−18.42.41

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/1/e1600615/DC1

    fig. S1. FTIR spectrum of HB-Pd/C and HB.

    fig. S2. TEM image of large particle formation after homogeneous Pd(TFA)2-catalyzed reaction.

    fig. S3. Hot filtration test of HB-Pd/C–catalyzed aerobic oxidation reaction.

    fig. S4. XPS spectra of CB-Pd/C before and after reaction in Pd 3d region.

    fig. S5. TEM morphology and size distribution of BB-Pd/C and catalytic behavior.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. FTIR spectrum of HB-Pd/C and HB.
    • fig. S2. TEM image of large particle formation after homogeneous Pd(TFA)2-catalyzed reaction.
    • fig. S3. Hot filtration test of HB-Pd/C–catalyzed aerobic oxidation reaction.
    • fig. S4. XPS spectra of CB-Pd/C before and after reaction in Pd 3d region.
    • fig. S5. TEM morphology and size distribution of BB-Pd/C and catalytic behavior.

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