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

Janet Chakkamadathil Mohandas, Edy Abou-Hamad, Emmanuel Callens, Manoja Samantaray, David Gajan, Andrei Gurinov, Tao Ma, Samy Ould-Chikh, Adam S. Hoffman, Bruce C. Gates, Jean-Marie Basset

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

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 Ta-2(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 H-1, C-13, Si-29, and N-15 at their natural abundances. The characterization data provide details of the synthesis chemistry, including evidence of (a) O-2 insertion into Ta-CH3 species on the support and (b) a binuclear to mononuclear transformation of species formed from Ta-2(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.
Original languageEnglish (US)
Pages (from-to)5650-5661
Number of pages12
JournalChem. Sci.
Volume8
Issue number8
DOIs
StatePublished - 2017

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We gratefully acknowledge the financial support provided by the King Abdullah University of Science and Technology (KAUST). We thank Dr Kun Li, Dr Nejib Hedili, and Dr Abdul-Hamid Emwas of the KAUST core labs for HRTEM, XPS, and NMR measurements, respectively, and Prof. Kazuhiro Takanabe for help with the ammonia treatments. We acknowledge Prof. Lyndon Emsley, EPFL, Switzerland, for helpful suggestions. We acknowledge beam time at beamline 4-1 of the Stanford Synchrotron Radiation Lightsource supported by the U.S. DOE Division of Materials Science under Contract No. DE-AC02-76SF00515.

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