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Title

Selective aerobic oxidation of 1,3‑propanediol to
3‑hydroxypropanoic acid using hydrotalcite
supported bimetallic gold nanoparticle catalyst
in water

Author(s)Mohammad, Mujahid; Nishimura, Shun; Ebitani,
Kohki

Citation

AIP Conference Proceedings, 1649: 58‑66

Issue Date

2015‑02‑27

Type

Conference Paper

Text version

publisher

URL

http://hdl.handle.net/10119/13707

RightsCopyright 2015 American Institute of Physics.
This article may be downloaded for personal use
only. Any other use requires prior permission of
the author and the American Institute of Physics.
The following article appeared in Mujahid
Mohammad, Shun Nishimura, Kohki Ebitani, AIP
Conference Proceedings (Proceeding), 1649, 58‑66(2015) and may be found at
http://dx.doi.org/10.1063/1.4913545

Description

Japan Advanced Institute of Science and Technology

Selective Aerobic Oxidation of 1,3-Propanediol to 3Hydroxypropanoic Acid using Hydrotalcite Supported
Bimetallic Gold Nanoparticle Catalyst in Water
Mujahid Mohammad1, 2 Shun Nishimura1 and Kohki Ebitani1, *1School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa
923-1292, Japan2

M. Tech (Chemical Synthesis and Process Technologies), Department of Chemistry, University of Delhi, Delhi110007, India*

Corresponding author: ebitani@jaist.ac.jp

Abstract. Selective oxidation of 1,3-propanediol (1,3-PD) to 3-hydroxypropanoic acid (3-HPA), an important industrial
building block, was successfully achieved using hydrotalcite-supported bimetallic Au nanoparticle catalysts in water at
343 K under aerobic and base-free conditions. The highest yield of 42% with 73% selectivity towards 3-HPA wasafforded by 1wt% Au0.8Pd0.2-PVP/HT catalyst.
Keywords. Selective aerobic oxidation, 1,3-Propandiol, 3-Hydroxypropanoic acid, AuPd bimetallic catalyst.

INTRODUCTION
3-Hydroxypropanoic acid (3-HPA) is classified as ω-hydroxyl-aliphatic carboxylic acid and a bifunctional, threecarbon organic compound which has been identified as a potent new generation chemical intermediate. It occupies
third position in the classification of the main strategic building blocks obtained from biological resources [1]. Dueto its bifunctionality, it can be converted into a number of high value chemicals (e.g. acrylic acid, poly-3-HPA,
propiolactone, polyesters etc.) [2], these are employed in the production of adhesives, fibers, and resins by simple
chemical transformations. It can further undergo selective oxidation of 3-HPA to give malonic acid (MA) and its
derivatives which together represent an important market.
Despite major research efforts, 3-HPA is still a rare and costly chemical commercialized as an aqueous solution
by few suppliers. 3-HPA has been synthesized via biological routes from 3-hydroxypropanaldehyde, glucose, andglycerol [3, 4]. Allyl alcohol can serve 3-HPA via selective oxidation and hydration reaction [5, 6]. Synthesis of 3HPA is also reported in patent literatures from β-propiolactone [7], 3-hydroxypropanaldehyde [8], and vinyl acetate[9]. Another patent shows that acrylic acid can undergo hydration reaction to give 3-HPA in water [10]. Behr et al.
showed an interesting pathway for the synthesis of 3-HPA from 1,3-propanediol (1,3-PD), an aliphatic diol, byselective oxidation over Pt and Pd based bi- and tri- metallic catalysts using a large quantity of NaOH and high O2
pressures [11]. Such a “non green” chemical route, results in the formation of products as sodium salts which
The Irago Conference 2014
AIP Conf. Proc. 1649, 58-66 (2015); doi: 10.1063/1.4913545© 2015 AIP Publishing LLC 978-0-7354-1291-0/$30.00

58requires excess energy consumption to obtain 3-HPA in Na-free form. There is therefore a need to develop a new
green strategy for the production of 3-HPA. This paper addresses the production of 3-HPA by selective aerobic
oxidation of 1,3-PD. 1,3-PD is obtained from glycerol [12] which is produced as a by-product during biodiesel
production [13], thereby making it an ideal substrate for the synthesis of 3-HPA.
Supported gold based bimetallic nanoparticles (NPs) catalysts have been used for the selective aerobic oxidationof alcohols [6, 14-19]. The recent studies commonly used polymer capped highly dispersed bimetallic NPs catalysts
like AuPd-PVA/TiO2 (PVA: Polyvinyl alcohol) [15], AuPt-PVA/MgO [16], and AuPd-PVA/C [17, 18]. A common
feature employed for the liquid phase aerobic oxidation of alcohols using Au catalyst involves the need for bases
such as NaOH and K2CO3 to activate the alcohols. From the view point of green chemistry, it is therefore desirable
to develop bifunctional catalysts combining NPs with solid base supports. It has been demonstrated thathydrotalcite-supported bimetallic AuPd NPs (AuPd-PVP/HT (PVP: polyvinylpyrrolidone)) are active for aerobic
oxidations of aromatic alcohols without external base additives in toluene solvent [19], suggesting synergy between
AuPd NPs and basic sites of the HT.
As a novel application of the AuPd-PVP/HT catalysts, we hereby wish to report the base-free and aerobic
oxidation of 1,3-PD toward 3-HPA in water catalyzed by heterogeneous and reusable AuPd-PVP/HT under mild
reaction conditions. Generally, oxidation of aliphatic primary alcohols is difficult rather than that of aromatic
alcohols [20]. Recently, Ide and Davis reported the oxidation of 1,3-PD over Pt/carbon catalyst to afford 3-HPA
with 11% yield (20% conversion) under 10 bar O2 in the presence of acetic acid at 343 K [21]. This paper describes
the highest 3-HPA yield of 42% (58% conversion) under an atmospheric O2 pressure in water at 343 K anddetermines apparent activation energy by kinetic approach to ascertain the influence of Pd atom on the oxidation of
1,3-PD, which were not reported in our previous paper [19].

EXPERIMENTAL
Chemicals
Hydrogen tetrachloroaurate tetrahydrate (HAuCl4•4H2O, 99% purity), Palladium chloride (PdCl 2, 99% purity),
25% Ammonia solution (NH3 aq.), potassium chloride (KCl), Ethylene glycol (EG) and sodium carbonate
decahydrate (Na2CO3•10H2O) were supplied by Wako Pure Chemical Ind. Ltd. 1,3-Propanediol (98% pure, further
purified by distillation before use, 1,3-PD) and 3-hydroxypropanoic acid (30% in water, 3-HPA) were purchasedfrom Tokyo chemical Ind. Ltd. Co. Polyvinylpyrrolidone (PVP, Mw= 58,000) and Mg-Al hydrotalcite (HT, Mg/Al=
5.03) was purchased from Acros Organics Co. and Tomita Pharmaceutical Co. Ltd., respectively.

Catalyst Preparation
Monometallic bare Au/HT catalyst was prepared by the deposition-precipitation method using NH3 aq. [22],followed by calcinations at 473 K. In brief, HT (1 g) was added to an aqueous solution of HAuCl 4 (1.2 mM, 40 ml)
with a vigorous stirring, and the pH of the solution was adjusted to 10 by addition of NH 3 aq. solution. The obtained
solution was vigorously stirred for 6 h followed by 30 min reflux at 373 K. The resulting solid was filtered, washedthoroughly with water, and dried at 473 K for 12 h. Finally, the ruby-colored solid catalyst was obtained.
Bimetallic 1wt% AuxPdy NPs protected by PVP agents were prepared by the polyol reduction method with EG
under reflux condition followed by the addition of HT according to the previous report [19]. For instance, thepreparation of Au0.8Pd0.2-PVP/HT (0.8wt% Au, 0.2wt% Pd) was as follows: An mixed aqueous solution (50 ml) of
PdCl2 (0.0188 mmol), KCl (0.1 g) and HAuCl4•4H2O (0.0406 mmol) was refluxed in the presence of PVP (0.58 g)
and EG (50 ml) for 2 h, thereafter, HT (1.0 g) was added to the formed colloidal dispersion to stabilize the formed
Au0.8Pd0.2-PVP NPs onto the surface of HT with an additional stirring for 1 h. The obtained catalyst was filtered,washed, and dried in vacuum overnight. The Pd content was varied in the range of 0 to 100%, and the total amountof both metals in the colloidal dispersion (x + y) was kept as 1wt%. The X-ray diffraction measurements confirmed
the crystal structure of both Au/HT and Au0.8Pd0.2-PVP/HT to be identical to the parent HT (Figure 1(a)). The total
amount of metal loading was determined to be 1.01wt% in Au/HT and 1.06wt% in Au 0.8Pd0.2-PVP/HT analyzed by
ICP-AES, respectively. Absence of surface plasmon resonance corresponding to Au NPs (480-580 nm) in the UVvis spectra of all AuxPdy-PVP NPs suggested Au-Pd alloy formation in AuxPdy-PVP NPs dispersed solutions (Figure1(b)). TEM

59

Au-PVP
Au0.2Pd0.8-PVP

0.14

Au0.4Pd0.6-PVP
Au0.6Pd0.4-PVP

0.12

Au0.8Pd0.2-PVP

Intensity

Absorbance

Au0.9Pd0.1-PVP
Pd-PVP

0.10

0.08

Au/HT
Au0.8Pd0.2-PVP/HT

0.06

HT

10

20

30

40

50

60

70

0.04
400

80

(a)

600

700

(b)
Au0.4Pd0.6-PVP/HT

Au/HT
Mean size = 3.3 nm

Au0.9Pd0.1-PVP/HT

500

Wavelength (nm)

2 Theta /degree

Mean size = 3.1 nm

Mean size = 2.6 nm

Au0.2Pd0.8-PVP/HT
Mean size = 2.7 nm

Pd1.0-PVP/HT

Au0.8Pd0.2-PVP/HT
Mean size = 2.5 nm

Mean size = 2.6 nm

Au0.6Pd0.4-PVP/HT
Mean size = 2.5 nm(c)
FIGURE 1. Results of characterization in (a) XRD patterns of Au/HT, Au0.8Pd0.2-PVP/HT, and HT support, (b) UV-vis spectraof AuxPdy NPs dispersed solution with various Au:Pd weight ratios, and (c) TEM images of monometallic and bimetallic Au
catalysts.

60

images indicated that the synthesized NPs were well-dispersed and stabilized onto the HT support in various x/ycases (Figure 1(c)).

Catalyst Characterization
The morphology of both monometallic and bimetallic Au catalyst was analyzed by transmission electron
microscopy (TEM; Hitachi H-7100) operating at 100 kV. Powdered X-ray diffraction patterns were obtained with a
Rigaku Smartlab X-ray diffractometer using Cu Kα radiation (λ = 0.154 nm) accelerated at 40 kV and 20 mA.
Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was obtained using Shimadzu ICPS-7000
ver.2 to estimate the real concentration of Au and Pd in Au/HT monometallic and Au xPdy-PVP/HT bimetallic
catalysts. The Ultraviolet and visible (UV-vis) spectra were measured by a Perkin-Elmer Lambda35 spectrometer atroom temperature with a light path length of 1 cm.

Aerobic oxidation of 1,3-propanediol
The oxidation of 1,3-PD was carried out in a 30 ml Schlenk flask attached to a reflux condenser. In a generalprocedure, 0.1 g catalyst in 7.5 ml water was added to the Schlenk flask, and purged with O 2 flow before reaction
under stirring (500 rpm) followed by the addition of 1 mmol of 1,3-PD. Subsequently, the reaction mixture wasstirred at desired temperature for a given reaction time under O 2 flow (10 ml min-1) at atmospheric pressure. After
that, the reaction mixture was diluted by adding 7.5 ml water, the resulting mixture was centrifuged and filteredusing a Milex-LG 0.20 μm syringe filter, and the products were analyzed by HPLC (WATERS 600 PUMP)
equipped with a refractive index detector. A Shodex RSpak KC-811 column was used in aqueous 0.1wt% H3PO4 as
the eluent at a flow rate of 1.0 ml min-1 at 323 K.
The catalyst was separated, washed with 15 ml of a 10% Na2CO3 aqueous solution followed by washing with 30
ml of water, and dried in vacuum overnight at room temperature before reuse.

RESESULTS AND DISCUSSION
Aerobic oxidation of 1,3-PD to 3-HPA was carried out using 1wt% AuxPdy-PVP/HT catalysts with varying
Au:Pd weight ratios (x : y). The results are summarized in Table 1 (entries 3-10). The bimetallic Au0.8Pd0.2-PVP/HTTABLE 1. Comparison of catalytic activities of hydrotalcite supported AuxPdy NPs for aerobic oxidation of 1,3-PD.a
Catalyst, O2
OH 343 K, 12 h

HO

O
HO

1,3-PD

Catalyst
Entry

O

[O]
OH

HO

[O]

Yield (Sel.) /%

O

OH
MA

3-HPA

Conv.
/%

O

Particle sizeb
/nm

OH

+ CO2

AA

Metal amountc/mmol g-1
Au
Pd
0.0513
0

TON

MA
3-HPA
Au/HT
36
30 (83)6 (17)
3.3
59
1
26
24 (93)2 ( 7)
95
2d
Au-PVP/HT
1
0
(
0)
0
(
0)
Agglomerates
0.043200
3
1.0
Au0.9Pd0.1-PVP/HT
45
30 (67)
3 ( 7)
3.1
0.05510.0141
43
4
Au0.8Pd0.2-PVP/HT
58
42 (73)10 (17)2.5
0.03960.021669
537
32 (86)5 (14)
1056d
Au0.6Pd0.4-PVP/HT
67
32 (48)18 (27)2.5
0.0301
0.042
44
7
Au
Pd
-PVP/HT
76
20
(26)
24
(32)
2.6
0.0270
0.093
19
8
0.4
0.6
Au0.2Pd0.8-PVP/HT
61
18 (30)14 (23)2.7
0.01270.122
14
9
Pd1.0-PVP/HT
17
15 (88)0 ( 0)
2.6
0
0.156
10
10
a
Reaction conditions : 1,3-PD (1.0 mmol), H2O (7.5 ml), 1wt% Catalyst (0.1 g, d0.05 g), O2 flow (10 ml min-1), 343 K, 12 h,b
Determined by TEM measurements about 270 NPs for each sample (See Figure 1(c)). cEstimated by ICP-AES analysis.
3-HPA: 3-hydroxypropanoic acid, MA: malonic acid, Au0.8Pd0.2-PVP/HT: 0.8wt% Au and 0.2wt% Pd composed the catalyst.

61

showed the highest catalytic activity among the various AuxPdy-PVP/HTs (entries 5) whereas Au1.0-PVP/HT showedno activity (entry 3). The monometallic Pd1.0-PVP/HT catalyst was moderately active (entry 10). An increase in theamount of Pd content from 0.1wt% to 0.6wt% resulted in an increase of 1,3-PD conversion, leading to decrease in
the yield and selectivity for 3-HPA by overoxidation to MA (entries 4, 5, 7, 8).
It is interesting to note that the yield of 3-HPA reached 42% over bimetallic Au0.8Pd0.2-PVP/HT catalyst with asmall decrease in selectivity from 83% to 73% and an increase in conversion from 36% to 58% when compared withmonometallic bare Au-supported HT (Au/HT) (entries 1 and 5). It has been shown that the catalytic performance of
Au NPs has been enhanced markedly by alloying with a second metal [16-19]. The turnover number per total metal(TON) for the oxidation of 1,3-PD using bimetallic Au0.8Pd0.2-PVP/HT (0.05 g) was calculated to be 105 at 343 K
for 12 h with 32% yield and 86% selectivity (entry 6).
Time profiles for the oxidation reaction of 1,3-PD over the Au/HT and Au0.8Pd0.2-PVP/HT catalysts at 343 K areplotted in Figure 3(a). With an increased reaction time, the 1,3-PD conversion increased and the selectivity of 3HPA gradually decreased due to further oxidation of the primary hydroxyl group of 3-HPA to MA. The highest
yield (42%) with 73% selectivity of 3-HPA and 58% conversion of 1,3-PD was achieved after 12 h of the reaction
over Au0.8Pd0.2-PVP/HT catalyst. It was also observed that the Au0.8Pd0.2-PVP/HT exhibited a higher activity thanthat of Au/HT in all steps. In other word, the reaction rate on bimetallic Au 0.8Pd0.2-PVP/HT catalyst was faster thanmonometallic Au/HT catalyst for aerobic oxidation of 1,3-PD.
80

100

Au/HT

70

Yield of 3-HPA/ %Au0.8Pd0.2-PVP/HT

50

60

Au0.8Pd0.2-PVP/HT
40

40

30

Au/HT

20
20

Selectivity of 3-HPA/ %

80
60

10
0

0
0

5

10

15

20

25

Time / h

(b)

50

50

40

40

Yield of 3-HPA / %% yield of 3-HPA

(a)

30

20

10

0

30

20

10

0
0

5

10

15

20

25

0

Time / h

5

10

15

20

25

Reaction time/ h

(c)

(d)

FIGURE 3. In the selective oxidation of 1,3-PD to 3-HPA in water, (a)Time profiles for Au/HT (1wt% Au) and Au0.8Pd0.2PVP/HT (0.8wt% Au and 0.2wt% Pd), and (b) Recyclability of 1wt% Au0.8Pd0.2-PVP/HT catalyst. Time courses of 1wt%
Au0.8Pd0.2-PVP/HT (closed circle) were also plotted with different two cases: (c) the catalyst was removed at 2 h (open circle) or(d) in the presence of TEMPO (15 mg) (open circle). Reaction conditions: 1,3-PD (1 mmol), catalyst (0.1 g), water (7.5 ml), 343
K, O2 flow (10 ml min-1).

62Normalized absorbance / a.u.

The reusability of the Au0.8Pd0.2-PVP/HT catalyst was tested and was found to be reusable up to three times
without significant loss in its catalytic activity and selectivity (Figure 3(b)). There was few observable change in theparticle size of Au0.8Pd0.2 alloy around at 2.5 nm after the reaction whereas the Au/HT showed a slight increase in
the mean particle size from 3.3 nm to 3.5 nm.
The possibility of catalyst leaching was ruled out by carrying out successive reactions after removal of solid
Au0.8Pd0.2-PVP/HT catalysts from the solution. Further continuation of the reaction after catalyst removal resulted inno significant increase in the yield of 3-HPA (Figure 3(c)). These results indicate that the present oxidation reactionsof 1,3-PD are truly heterogeneous.
In order to understand the reaction pathway over the Au0.8Pd0.2-PVP/HT catalyst, an investigation using a radical
scavenger, TEMPO, (2,2,6,6-tetramethyl piperidin-1-yl)oxidanyl, was performed. In the reaction using Au0.8Pd0.2PVP/HT, TEMPO (0.1 mmol) moderately influenced the oxidation rate of 1,3-PD with no significant change in 3HPA yields after 12 h (Figure 3(d)). This indicates that the dominant reaction mechanism does not involve theformation of a carbon centered free radical, in which case the yield of 3-HPA would have decreased in the presenceof TEMPO at the end of the reaction. This is in agreement with our report of aerobic oxidation of alcohols over
AuPd-PVP/HT catalyst [19].
The comparison of the reaction results for Au/HT and AuxPdy-PVP/HT suggests that Pd content in the AuxPdyPVP/HTs has a strong influence on the catalytic activity. It has been observed that the difference in ionization
potentials of Au and Pd causes the electron transfer from Pd to Au thereby creating partial negative charges on Au
and partial positive charges on Pd in PVP stabilized Au-Pd bimetallic catalysts [19]. Au L3-edge X-ray adsorption
near-edge structure (XANES) features of AuxPdy-PVP/HTs are shown in Figure 4. Lower intensities in AuxPdyPVP/HTs than Au-PVP/HT and Au foil in the white-line (WL) area, which attributed to the possibility for electrontransition from 2p to 5d state in Au atoms in the sample, indicated that the Au xPdy-PVP/HTs possessed muchnegativity in 5d state of Au atoms than Au1.0-PVP/HT and Au foil. Thus, these indicated that Au atoms in bimetallic
samples increased electronic charges in 5d state in compare with Au foil and Au 1.0-PVP/HT. The evolution of thesepartial charges may stabilize the transition state which could explain the higher activity of Au xPdy-PVP/HT catalyst
than Au/HT in the aerobic oxidation of 1,3-PD to 3-HPA.

Photon energy / keV

FIGURE 4. Au L3-edge XANES features of AuxPdy-PVP/HTs with references of Au foil and Au2O3.

Based on the above results, we propose a reaction mechanism involving the formation of an alkoxideintermediate (Figure 5). Firstly, O2 molecule is activated on AuG- to form AuO- peroxo and/or AuO2- superoxo
species [23, 24]. Dissociative adsorption of 1,3-PD on AuPd sites forms AuPd-alkoxide species. This step is
promoted by basic sites on hydrotalcite surface [19, 22]. The Au oxo species then abstract the hydrogen on the α-

63

B

B

Hydrotalcite

O2 1) Activation of O2
G-

O

O

HO
B

H 2O
1/2 O2OH

B

Hydrotalcite2) Alkoxide formation

4) Re-oxidation

H
O

G-

OH

HOH 2CH2 C

O

O

O

H

H
B

B

B

Hydrotalcite

B

Hydrotalcite3) Beta-Hydride elimination

H
HO

OH

HT
O

HO
OH
1,1,3- Propanetriol

H 2O

3-HydroxypropanalO

Au 0.8Pd 0.2 -PVP/HTHO

1/2 O 2OH
3-HPA

FIGURE 5. Proposed mechanism for aerobic oxidation of 1, 3-PD to 3-HPA using the 1wt% Au0.8Pd0.2-PVP/HT catalyst.

carbon leading to β-hydride elimination to give carbonyl compound (which subsequently, in situ is converted into 3HPA) and Au-hydroperoxide species. Reaction of O2 with the Au-hydroperoxide forms H2O and regenerates active
Au species to complete the catalytic cycle.
The O2 flow rate (10-50 ml min-1) did not influence the oxidation rate of 1,3-PD, indicating that the O2 activation
steps are fast. Therefore, the rate-determining step is proposed to be the β-hydride elimination step [19, 22, 25-27].
The rate constant k were determined at various temperatures assuming a first-order kinetics with respect to 1,3-PD
-0.2

-0.4

-0.3
-0.4

-0.6

lnC1,3-PD[mmol]

lnC1,3-PD(mmol)

-0.5
-0.6
-0.7
-0.8

333 K
343 K
358 K
373 K

-0.9
-1.0
-1.1
-1.2

-0.8

-1.0

333 K
343 K
358 K
373 K

-1.2

-1.4

-1.3
6

8

10

12

14

16

18

20

6

8

10

12

Time/ hTime / h

(a)

(b)

14

16

18

FIGURE 6. Plots of lnC1,3-PD [mol] vs time for (a) Au/HT, and (b) Au0.8Pd0.2-PVP/HT catalysts. Reaction conditions: 1,3-PD(1 mmol), 1wt% catalyst (0.1 g), water (7.5 ml), O2 flow (10 ml min-1).

64

FIGURE 7. Arrhenius plots for the oxidation of 1,3-PD over Au/HT and Au0.8Pd0.2-PVP/HT catalysts.

amount (Figure 6(a) and (b)). The Arrhenius plots (Figure 7) show that the activation energies for the Au/HT and theAu0.8Pd0.2-PVP/HT are 37.1 and 26.1 kJ mol-1, respectively. This indicates that the synergy between Au and Pd
atoms in nanoparticles may facilitate the slow β-hydride elimination step.

CONCLUSIONSWe showed that 1wt% Au0.8Pd0.2-PVP/HT catalyst prepared by a polyol reduction method is more active than
1wt% bare Au/HT prepared by a deposition-precipitation method for the selective oxidation of 1,3-PD to 3-HPA.
Alloying Au with Pd has been shown to increase the yield of 3-HPA with high conversion of 1,3-PD. We found that
the Au0.8Pd0.2-PVP/HT catalyst decreases activation energy in the rate-determination step for the aerobic oxidationof 1,3-PD and it leads nice activity in comparison with bare Au/HT catalyst. Finally, it was found that our
Au0.8Pd0.2-PVP/HT catalyst is able to oxidize not only aromatic alcohols in toluene but also aliphatic 1,3-PD inwater solvent.

ACKNOWLEDGMENTS
MM gratefully acknowledges support from the grant from dual masters program between JAIST-DU. SN is
thankful for the supports from 2012 Intellectual Property Highway Promotion of the Japan Science and Technology
Agency (JST), Japan, and the Grant-in-Aid for Young Scientist (B) (No. 25820392) support by the Ministry of
Education, Culture, Sports, Science, and Technology (MEXT), Japan. KE appreciates the Grant-in-Aid for Scientific
Research (C) (No. 25420825) support by the MEXT, Japan. Au L 3-edge XANES features were obtained at the BL9C of KEK-PF under the approval of the Photon Factory Program Advisory Committee (Proposal No. 2013G586) inJapan.

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