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. Issue 8 (20th June 2017)

• Record Type: Journal Article
• Authors: Mohandas, Janet C.; Abou-Hamad, Edy; Callens, Emmanuel; Samantaray, Manoja K.; Gajan, David; Gurinov, Andrei; Ma, Tao; Ould-Chikh, Samy; Hoffman, Adam S.; Gates, Bruce C.; Basset, Jean-Marie
• Is Part Of: Chemical science. Volume 8:Issue 8(2017)
• Page Start: 5650
• Page End: 5661
• Publication Date: 2017-06-20
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c7sc01365e
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : SOMC is exploited for synthesizing very fine nanoparticles of Ta x N y /TaO x N y on silica, elucidating the strategies with DNP SENS and EXAFS. Abstract : Air-stable catalysts consisting of tantalum nitride nanoparticles represented as a mixture of Ta x N y and TaO x N y 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 1 H, 13 C, 29 Si, and 15 N 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% H2 O2 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 Ta x N y /TaO x N y .