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Synthesis of Supported Pd-0 Nanoparticles from a Single-Site Pd2+ Surface Complex by Alkene Reduction

TitleSynthesis of Supported Pd-0 Nanoparticles from a Single-Site Pd2+ Surface Complex by Alkene Reduction
Publication TypeJournal Article
Year of Publication2018
AuthorsMouat, AR, Whitford, CL, Chen, BR, Liu, SS, Perras, FA, Pruski, M, Bedzyk, MJ, Delferro, M, Stair, PC, Marks, TJ
JournalChemistry of Materials
Date Published02
Type of ArticleArticle
ISBN Number0897-4756
Accession NumberWOS:000425840500052
Keywordsatomic layer deposition, chemistry, dynamic nuclear-polarization, ethylene polymerization, in-situ, Materials Science, metal catalyst, molecular-oxygen, organometallic chemistry, palladium nanoparticles, particles, selective oxidation, structure sensitivity

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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