Communications
A Fourier transform (FT) of the Au LIII-edge EXAFS spectra is
plotted in Figure S9(B) (Supporting Information). The Au–Pd
bimetallic catalysts showed intense doublet peaks at 2.1 and
2.9 as compared to gold foil and Au100-DDAO/HT. The ap-
pearance and intensification of the doublet with increase in
palladium content is an indication of Au–Pd bonds[24a,25b] in
Au–Pd bimetallic NP-based heterogeneous catalysts.[28] The pal-
ladium XAS features in K- and LIII-edges (Supporting Informa-
tion, Figure S10) also supports the notion of strong correla-
tions between palladium and gold. The two features at 24389
and 24428 eV in the Pd K-edge XANES spectra are found at
lower energy for Au–Pd bimetallic catalysts than for palladium
foil [Figure S10(A)].[29] Furthermore, the FT of Pd K-edge EXAFS
spectra [Supporting Information, Figure S11(B)] shows splitting
of the peak at 2–3 with increase in gold content.[30] These
shifts can be attributed to changes in electronic structure
around palladium by alloying with gold.[26] From these obser-
vations, we infer that the electronic properties of gold and pal-
ladium are significantly changed in the bimetallic catalysts as
a consequence of Au–Pd interactions (bond formation). These
particular interactions or Au–Pd nanoalloy centers may be re-
sponsible for the high catalytic activity of Au40Pd60-DDAO/HT in
the selective oxidation of HDO to HCA.
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In summary, a series of hydrotalcite-supported N,N-dimethyl-
dodecylamine N-oxide (DDAO)-capped bimetallic Au–Pd nano-
particles are prepared, and their catalytic activities are explored
for oxidation of 1,6-hexanediol (HDO) to 6-hydroxycaproic acid
(HCA). A maximum HCA yield of 81% at an HDO conversion of
87% was achieved with a reusable Au40Pd60-DDAO/HT catalyst
in basic aqueous media using H2O2. Spectroscopic investiga-
tions suggest that interactions between gold and palladium
provide the active sites responsible for selective oxidation of
the primary OH group of the C6 aliphatic diol, HDO.
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Acknowledgements
[15] H. Choudhary, S. Nishimura, K. Ebitani, ChemCatChem 2015, 10.1002/
This work was partially supported by a Young Scientists (B) grant
(25820392) and
a Grant-in-Aid for Scientific Research (C)
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[18] The HPLC analysis of the reaction mixture denied the presence of any
other water-soluble products after the reaction. Also, both 1H- and
13C NMR spectroscopy (Figure S3) of the reaction mixture extracted by
the organic solvent (chloroform)only identified the three compounds of
HDO, HCA and AA.
(25420825) of the Ministry of Education, Culture, Sports, Science
and Technology (MEXT), Japan. H.C. thanks JSPS for a fellowship.
XAS was performed at the BL-9C (Au LIII-edge) and the BL-9A (Pd
LIII-edge) of Photon Factory at High Energy Accelerator Research
Organization (KEK-PF), Tsukuba, Japan, under Proposals
2013G586 and 2012G763. The BL01B1 in the SPring-8 with the
approval of the Japan Synchrotron Radiation Research Institute
(JASRI) (2014B1472) was also used for Pd K-edge XAS studies.
Keywords: gold · hydrotalcites · oxidation · palladium ·
renewable resources
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