Journal
CHEMISTRY OF MATERIALS
Volume 30, Issue 3, Pages 1032-1044Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.chemmater.7b04909
Keywords
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Funding
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-FG02-03ER154757]
- NSF [DMR-1334928]
- Spedding Fellowship - Ames Laboratory's LDRD program
- U.S. Department of Energy [DE-AC02-07CH11358, DE-FG02-03ER15457]
- National Sciences and Engineering Research Council of Canada (NSERC)
- government of Canada
- Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource [NSF NNCI-1542205]
- MRSEC program at the Materials Research Center [NSF DMR-1121262]
- International Institute for Nanotechnology (IIN)
- Keck Foundation
- State of Illinois, through the IIN
- U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences [DE-AC02-06CH11357]
- E. I. duPont de Nemours Co.
- Northwestern University
- Dow Chemical Co.
- State of Illinois through the Department of Commerce
- State of Illinois through the Board of Education (HECA)
- US National Science Foundation
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A surface metal-organic complex, (-AlOx)Pd(acac) (acac = acetylacetonate), is prepared by chemically grafting the precursor Pd(acac)(2) onto gamma-Al2O3 in toluene at 25 degrees C. The resulting surface complex is characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and dynamic nuclear polarization surface-enhanced solid-state nuclear magnetic resonance spectroscopy (DNP SENS). This surface complex is a precursor in the direct synthesis of size-controlled Pd nanoparticles under mild reductive conditions and in the absence of additional stabilizers or pretreatments. Indeed, upon exposure to gaseous ethylene or liquid 1-octene at 25 degrees C, the Pd2+ species is reduced to form Pd-0 nanoparticles with a mean diameter of 4.3 +/- 0.6 nm, as determined by scanning transmission electron microscopy (STEM). These nanoparticles are catalytically relevant using the aerobic 1-phenylethanol oxidation as a probe reaction, with rates comparable to a conventional Pd/Al2O3 catalyst but without an induction period. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reaction mass spectrometry (TPR-MS) reveal that the surface complex reduction with ethylene coproduces H-2, acetylene, and 1,3-butadiene. This process reasonably proceeds via an olefin activation/coordination/insertion pathway, followed by beta-hydride elimination to generate free Pd-0. The well-defined nature of the single-site supported Pd2+ precursor provides direct mechanistic insights into this unusual and likely general reductive process.
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