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From single-site tantalum complexes to nanoparticles of TaxNy and TaOxNy supported on silica: elucidation of synthesis chemistry by dynamic nuclear polarization surface enhanced NMR spectroscopy and X-ray absorption spectroscopy

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Abstract

Air-stable catalysts consisting of tantalum nitride nanoparticles represented as a mixture of TaxNy and TaOxNy with diameters in the range of 0.5 to 3 nm supported on highly dehydroxylated silica were synthesized from TaMe5 (Me = methyl) and dimeric Ta2(OMe)10 with guidance by the principles of surface organometallic chemistry (SOMC). Characterization of the supported precursors and the supported nanoparticles formed from them was carried out by IR, NMR, UV-Vis, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopies complemented with XRD and high-resolution TEM, with dynamic nuclear polarization surface enhanced NMR spectroscopy being especially helpful by providing enhanced intensities of the signals of 1H, 13C, 29Si, and 15N at their natural abundances. The characterization data provide details of the synthesis chemistry, including evidence of (a) O2 insertion into Ta–CH3 species on the support and (b) a binuclear to mononuclear transformation of species formed from Ta2(OMe)10 on the support. A catalytic test reaction, cyclooctene epoxidation, was used to probe the supported nanoparticles, with 30% H2O2 serving as the oxidant. The catalysts gave selectivities up to 98% for the epoxide at conversions as high as 99% with a 3.4 wt% loading of Ta present as TaxNy/TaOxNy.

Graphical abstract: From single-site tantalum complexes to nanoparticles of TaxNy and TaOxNy supported on silica: elucidation of synthesis chemistry by dynamic nuclear polarization surface enhanced NMR spectroscopy and X-ray absorption spectroscopy

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Publication details

The article was received on 27 Mar 2017, accepted on 08 Jun 2017 and first published on 08 Jun 2017


Article type: Edge Article
DOI: 10.1039/C7SC01365E
Citation: Chem. Sci., 2017, Advance Article
  • Open access: Creative Commons BY-NC license
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    From single-site tantalum complexes to nanoparticles of TaxNy and TaOxNy supported on silica: elucidation of synthesis chemistry by dynamic nuclear polarization surface enhanced NMR spectroscopy and X-ray absorption spectroscopy

    J. C. Mohandas, E. Abou-Hamad, E. Callens, M. K. Samantaray, D. Gajan, A. Gurinov, T. Ma, S. Ould-Chikh, A. S. Hoffman, B. C. Gates and J. Basset, Chem. Sci., 2017, Advance Article , DOI: 10.1039/C7SC01365E

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