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 spectroscopyElectronic supplementary information (ESI) available: Complete experimental procedures, supporting characterization techniques, data and the details for the prepared compounds are provided. See DOI: 10.1039/c7sc01365e

• Main 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
• Format: Journal Article
• Language: English
• Published: 24-07-2017
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c7sc01365e

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 TaMe
5
(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
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) O
2
insertion into Ta-CH
3
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% H
2
O
2
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
.
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.