Electrosynthesis of diphenyl carbonate catalyzed by Pd2+/0 (in situ NHC) redox catalyst promoted at Au anode

Article abstract of DOI:10.1007/s11164-015-1975-8

The effects of Au anodes on electrochemical carbonylation of phenol with CO (1 atm) to diphenyl carbonate (DPC) catalyzed by Pd (in situ NHC) electrocatalyst were studied under galvanostatic electrolysis conditions. Au supported on carbon materials (Au/carbon) were effective anodes for oxidation of the homogeneous Pd electrocatalyst. Various carbon materials, Vulcan XC-72 carbon black (XC72), activate carbon, Ketjenblack, and graphene nanoplatelets (graphene- 1, -2, -3) were tested as a support for Au. The Au/graphene-3 was the most effective anode for DPC formation. Effects of Au loadings and reducing agents (H₂ and NaBH₄) on the reactivity of the Au/graphene-3 anode for the DPC formation were studied and the materials were characterized using XRD spectroscopy and TEM analysis. These experimental facts indicated that small Au particles on the surface of graphene were superior for the DPC synthesis by the Pd (in situ NHC) electrocatalyst.

Full text of DOI:10.1007/s11164-015-1975-8

Res Chem Intermed
DOI 10.1007/s11164-015-1975-8
Electrosynthesis of diphenyl carbonate catalyzed
by Pd2+/0 (in situ NHC) redox catalyst promoted
at Au anode
Ryoichi Kanega1 Hitoshi Ogihara2 Ichiro Yamanaka1,2
•
•
Received: 7 July 2014 / Accepted: 4 December 2014
ꢀ Springer Science+Business Media Dordrecht 2015
Abstract The effects of Au anodes on electrochemical carbonylation of phenol
with CO (1 atm) to diphenyl carbonate (DPC) catalyzed by Pd (in situ NHC)
electrocatalyst were studied under galvanostatic electrolysis conditions. Au sup-
ported on carbon materials (Au/carbon) were effective anodes for oxidation of the
homogeneous Pd electrocatalyst. Various carbon materials, Vulcan XC-72 carbon
black (XC72), activate carbon, Ketjenblack, and graphene nanoplatelets (graphene-
1, -2, -3) were tested as a support for Au. The Au/graphene-3 was the most effective
anode for DPC formation. Effects of Au loadings and reducing agents (H2 and
NaBH4) on the reactivity of the Au/graphene-3 anode for the DPC formation were
studied and the materials were characterized using XRD spectroscopy and TEM
analysis. These experimental facts indicated that small Au particles on the surface of
graphene were superior for the DPC synthesis by the Pd (in situ NHC)
electrocatalyst.
Keywords Diphenyl carbonate ꢀ Pd electrocatalyst ꢀ Au anode ꢀ Graphene support
Introduction
Diphenyl carbonate (DPC) is a key material for the production of polycarbonate
[1, 2], which is one of the most useful engineering plastics due to its good heat
resistance, mechanical properties, and transparency. In industrial processes, DPC is
manufactured from phosgene or dimethyl carbonate and phenol (PhOH). However,
&
Ichiro Yamanaka
yamanaka@cms.titech.ac.jp
1
2
Department of Applied Chemistry, Tokyo Institute of Technology, Tokyo 152-8552, Japan
Department of Chemistry and Materials Science, Tokyo Institute of Technology,
Tokyo 152-8552, Japan
123

R. Kanega et al.
these processes have disadvantages such as the use of toxic phosgene and
consumption of a large amount of energy. Therefore, the development of direct
oxidative carbonylation of PhOH with carbon monoxide and oxygen is an attractive
subject from the viewpoint of green chemistry. So far, direct oxidative carbony-
lation of PhOH to DPC using homogeneous catalysts [3–7] and heterogeneous
catalysts [8–14] have been reported. However, direct oxidative carbonylation
requires an under pressure condition around 100 atm at higher temperature around
373 K and results in hydrolysis of DPC by water produced from oxygen. Recently,
we have proposed the direct electrochemical carbonylation of PhOH to DPC by
using Pd electrocatalysts [15–19]. This new synthesis of DPC was conducted in
mild reaction conditions without the production of water; therefore, the hydrolysis
of DPC did not proceed. Active homogeneous electrocatalyst of Pd coordinated N-
heterocyclic carbene (NHC) has recently been found and, moreover, in situ
generated NHC from imidazolium chlorides has been found to be an effective
ligand. Active NHC ligands for PdCl2(CH3CN)2 were 1,3-di-mesitylimidazol-2-
ylidene (IMes), 1,3-di-isopropylimidazol-2-ylidene (IPr), and active precursors of
in situ NHC were 1,3-di-alkyl-imidazolium chloride (IMesHCl, IPrHCl and It-
BuHCl) and 1,3-di(tert-butyl)imidazoline chloride (SIt-BuHCl) [9, 10]. Efficiencies
of ligands for Pd electrocatalyst were in situ IMes \ IMes \ in situ IPr \ in situ It-
Bu \ in situ SIt-Bu. Therefore, a PdCl2(in situ SIt-Bu) electrocatalyst was used in
this work.
The electrochemical carbonylation of PhOH to DPC proceeds through the
following reactions.
2PhOH þ CO þ Pd2 þ ðLÞ ! DPC þ 2Hþ þ Pd0ðLÞ in solution
Pd0ðLÞ ! Pd2þðLÞ þ 2eꢁ at Au=carbon anode
2Hþ þ 2eꢁ ! H2 at Pt cathode
ð1Þ
ð2Þ
ð3Þ
CO þ H2O þ Pd2þðLÞ ! CO2 þ 2Hþ þ Pd0ðLÞ
ðL: NHC ligandsÞin solution
ð4Þ
Oxidative carbonylation of PhOH with CO to DPC proceeds by Pd2? (Eq. 1).
Electrochemical oxidation of Pd0 to Pd2? proceeds at the Au anode (Eq. 2).
Reduction of H? to H2 proceeds at the cathode (Eq. 3). The formation of DPC
(Eq. 1) was promoted by H? acceptor (sodium phenoxide). In addition, oxidation of
CO to CO2 with H2O proceeds by Pd2? (Eq. 4). In our previous works, Au wire was
used as the anode and a surface area of the Au wire was not large. If a new Au anode
having higher surface area is used, an oxidation rate of Pd0 to Pd2? (Eq. 2) will
increase and the DPC formation rate will be accelerated. In this work, Au-supported
carbon materials were prepared and were used for the anode [20, 21]. Effects of the
Au/carbon anodes on the DPC formation catalyzed by Pd (in situ SIt-Bu)
electrocatalyst were studied.
123

Electrosynthesis of diphenyl…
Experimental
Anode preparation
An Au anode for oxidation of Pd complex electrocatalyst was prepared from
Au/carbon materials by the hot press method [15, 16]. Au/carbon materials were
prepared by a conventional impregnation method. Activated carbon (AC,
1420 m2 g-1, Wako Pure Chemical Industries), Vulcan XC-72 carbon black
(XC72, 290 m2 g-1, Cabot Co.), Ketjenblack EC600JD (KBJD, 1100 m2 g-1, Kao
Co.) and three types of graphene nanoplatelets (graphene-1, 340 m2 g-1; graphene-
2, 470 m2 g-1; graphene-3, 710 m2 g-1, Strem Chemicals) were used as a carbon
support of Au.
A typical preparation procedure of Au/graphene was described below. An
aqueous solution of HAuCl4 was mixed with graphene powder. Then, the solution
was dried up to powder in air at 373 K. The HAuCl4/graphene powder was reduced
with H2 (1 atm.) in a quartz reactor for 2 h at 573 K. Au loadings on graphene were
1.0, 5.0, 10.0, 15.0, and 25.0 wt%.
In addition to the impregnation method, Au/graphene material was prepared by
the deposition of Au on graphene using a reducing agent of NaBH4, according to a
previous report [21]. After graphene powder was added into a HAuCl4 aqueous
solution (0.1 mM), the mixture was stirred for 30 min at 298 K. NaOH aqueous
Fig. 1 Diagram of one-compartment electrolysis cell for DPC synthesis
123

R. Kanega et al.
solution (2.0 M) was added into the mixture to adjust pH at 10. An aqueous solution
of NaBH4 (0.1 M) was quickly added into the mixture under vigorous stirring. After
filtration, the obtained Au/graphene was washed with water (25 ml 9 3) and dried
in decompression. The Au loading on graphene was 10.0 wt%.
The anode was prepared by the hot-press method [15, 16]. An Au/graphene
powder (47 mg, Au 60 lmol), vapor-grown carbon fiber (125 mg, VGCF), and of
polytetrafluoroethylene powder (40 mg, PTFE, F-104 Daikin Co.) were well mixed
and kneaded to a clay lump. The clay lump was pressed and shaped on the hot-plate
to a sheet anode (Au/graphene ? VGCF anode). The geometric area of the anode
was 8 cm2.
Electrolysis procedure
Electrochemical carbonylation was conducted using a one-compartment elec-
trolysis cell. The cell was fabricated from an Au/carbon ? VGCF anode, a platinum
wire cathode, a gas inlet and outlet, and a sampling port, as shown in Fig. 1. An
electrolyte solution is PdCl2(CH3CN)2 (60 lmol), 1,3-di(tert-butyl)imidazoline
chloride (SIt-BuHCl, 180 lmol), PhOH (30 mmol), sodium phenoxide (PhONa,
0.5 mmol) and CH3CN (40 ml). PhONa functions as an electrolyte and a promoter
for the DPC formation [16]. The solution was dried using molecular sieves 3A, and
content of impurity water in the solution was kept under 50 ppm. Dry CO (1 atm)
passing through a cold trap (197 K) was introduced into the electrolyte solution. The
Au/graphene ? VGCF anode was sandwiched between two glassy carbon plates
(current collector, 5 9 20 9 1 mm) and suspended in the solution. Galvanostatic
electrolysis of the solution was conducted under galvanostatic electrolysis from 1 to
5 mA for 3 h at 298 K by use of an HZ-5000 electrochemical instrument system
(Hokuto Denko Co.).
Product analyses
Products in the electrolysis solution (DPC, etc.) were identified and quantified by
gas chromatographic techniques using a Shimadzu GC-2010 [ZB-1capillary column
(0.25 ø 9 30 m), FID detector, He carrier gas] and an Agilent EZ-Chrome with a
SS420X module. Products in gas phase (CO, CO2 and H2) were analyzed by an
online gas chromatograph (GL-Science GC-323), CO2 and CO analysis; Porapak-Q
column (4 ø 9 2 m), TCD detector, He carrier gas, H2 analysis; activated carbon
column (4 ø 9 2 m), TCD detector, Ar carrier gas.
In this study, homogeneous Pd2? electrocatalyst was used for carbonylation of
PhOH. According to our previous reports [17], DPC formation consisted of two
different reaction paths, stoichiometric carbonylation and electrochemical carbony-
lation. The stoichiometric DPC formation finished within 10 min (Eq. 1). CO2 was
also stoichiometrically formed until 60 min (Eq. 3). In electrolysis condition,
Pd0(L) was oxidized to Pd2?(L) at the anode (Eq. 2) and DPC was produced after
10 min (Eqs. 1, 2). CO2 was also electrochemically produced after 60 min (Eqs. 1,
3). The current efficiencies to DPC and CO2 formation were calculated kinetic
slopes after 10 and 60 min, respectively.
123

Electrosynthesis of diphenyl…
Characterization of Au/carbon
The Au/carbon materials were characterized using transmission electron
microscopy (TEM) and X-ray diffraction spectroscopy (XRD). An image of Au
particles on graphene was obtained by TEM (JEM-2010F (JEOL) microscope
equipped with a detector (Genesis, EDAX) for energy-dispersive X-ray spec-
troscopy). The crystal structure of the Au particle was studied by XRD analysis
(MiniFlex 600/TISS (Rigaku) diffractionmeter using a Cu-Ka radiation).
Results and discussion
As mentioned in the introduction, the Au/carbon ? VGCF anodes were applied for
the electrochemical carbonylation of PhOH catalyzed by the homogeneous Pd
(in situ SIt-Bu) electrocatalyst in this work. The AC, XC72, KBJD and graphene-1,
-2, -3 materials were used as a carbon support. The XRD spectra of Au/carbon
materials are indicated in Fig. 2. All the diffraction peaks observed in the Au/carbon
were assignable to Au metal and graphite structure. Diffraction lines at 2h = 38, 44,
67, 78, 82, and 98ꢁ corresponded to the crystal planes of (111), (200), (220), (311),
(222), and (400) facets of the face-centered cubic structure of Au metal,
respectively. Diffraction peaks at 2h = 27ꢁ corresponded to graphite (002). The
XRD spectra indicated that Au species on carbon surface were present as Au metal
and (111) plane was the major orientation in all the Au/carbon materials.
Specific surface areas of carbon supports and the average crystalline sizes of Au
calculated from (111) plane using Scherer’s equation are indicated in Table 1. The
average crystalline sizes of Au on AC, XC72, KBJD and graphene-3 supports were
Fig. 2 XRD spectra of Au/carbon materials, a Au/XC72, b Au/KBJD, c Au/AC, d Au/graphene-3,
e Au/graphene-3 (NaBH4). Au metal: circle and graphite: square
123

R. Kanega et al.
123

Electrosynthesis of diphenyl…
almost the same (54–57 nm). In the case of graphene supports, the average
crystalline size decreased with increasing in the specific surface areas. As described
in the experimental section, the Au/carbon materials were prepared using the same
conventional impregnation method and reduction as H2. The preparation method
may be a primary factor to decide the crystalline size of Au. On the same nature of
carbon surface of graphene materials, the surface area may be secondary factor to
decide the crystalline size of Au.
Electrochemical carbonylation of PhOH using the Pd (in situ SIt-Bu) electro-
catalyst at the Au/carbon ? VGCF anodes was carried out under galvanostatic
condition at 1 mA. Figure 3 shows the time courses of (a) DPC and (b) CO2
formation by the electrochemical carbonylation of PhOH using the Au/
XC72 ? VGCF and Au/AC ? VGCF anodes. At the beginning of the reaction,
within 10 min the rapid formation of DPC by the stoichiometric formation with
initial Pd2?(in situ SIt-Bu) was observed. After 10 min, the DPC yield linearly
increased with the electrolysis time at the Au/XC72 ? VGCF anode. Thus, the
electrochemical formation rate and the current efficiency of DPC were calculated
from the slope after 10 min. On the other hand, an increase in DPC yield after
10 min was small for the Au/AC ? VGCF anode. With respect to CO2 formation,
the stoichiometric formation was slow and continued for 60 min. It was confirmed
that PdCl2(CH3CN)2 catalyzed the formation of DPC and CO2 because the products
were not formed without PdCl2(CH3CN)2. In order to confirm the role of Au/carbon,
a VGCF anode without Au was used for the carbonylation. In this case, only 3 lmol
of DPC and 1 lmol of CO2 were electrochemically formed, which indicated the
Au/carbon accelerated the electrochemical formations.
The Au/carbon anodes evidently affected the electrochemical formation of DPC;
therefore, other carbon supports were applied for the electrochemical carbonylation.
The stoichiometric and electrochemical yields of DPC and CO2 and the DPC current
efficiency at the Au/carbon anodes are summarized in Table 1. In addition, results at
Fig. 3 Time courses of DPC
and CO2 formation by 1 mA
galvanostatic electrolysis at
298 K. PdCl2(MeCN)2:
60
50
40
30
20
10
0
(b)
Au/AC
60 lmol, SIt-BuHCl :
180 lmol, PhOH : 30 mmol,
PhONa: 0.5 mmol CH3CN:
30 ml, P(CO): 101 kPa
Au/XC72
100
80
60
40
20
0
(a)
Au/XC72
Au/AC
0
1
2
3
4
Electrolysis time / h
123

R. Kanega et al.
the Au wire anode were also indicated at entry 1 in Table 1. The stoichiometric
yields of DPC using the anodes (entry 1, 3–7) were very similar, except for the Au/
AC ? VGCF anode (entry 2). On the other hand, the electrochemical yields of DPC
strongly depend on the Au anodes. The Au/XC72 ? VGCF (entry 3), Au/
KBJD ? VGCF (entry 4) and Au/graphene-3 ? VGCF (entry 7) anodes showed
high electrochemical DPC yields as well as that at the Au wire anode. The Au/
AC ? VGCF (entry 2), Au/graphene-1 ? VGCF (entry 5) and Au/graphene-
2 ? VGCF (entry 6) anodes showed low DPC yields. The stoichiometric and
electrochemical yields of CO2 were not large and did not depend on the Au anodes.
The current efficiency of DPC strongly depended on the Au anodes. The Au/
XC72 ? VGCF, Au/KBJD ? VGCF, Au/graphene-3 ? VGCF and Au wire anodes
showed high current efficiencies, corresponding to the electrochemical DPC yields.
As described above, the Au/XC72 ? VGCF, Au/KBJD ? VGCF and Au/gra-
phene-3 ? VGCF anodes were suitable for the DPC formation, especially the
Au/graphene-3 ? VGCF anode would be effective. The Au/AC ? VGCF anode
could not be effective for the DPC formation because the high adsorption capability
of AC might have an influence on the stoichiometric yield. In addition, it is likely
that poor conductivity of AC decelerated the electrochemical reaction. Except for
the Au/AC ? VGCF anode, the relativities of Au anodes of the DPC formation at
Au anodes seem to be related to the average crystalline sizes of Au. Very similar
sizes of Au crystalline were observed in entries 3, 4, and 7, and their electrochemical
DPC yields and DPC current efficiencies were similar. On the other hand, larger Au
crystalline sizes on graphene-1 and graphene-2 anode were observed and their
carbonylation activities were inferior activities for the DPC formation.
Among the Au/carbon materials prepared by the impregnation method and
reduction with H2 (entry 2–7), the Au/graphene-3 ? VGCF anode was suitable for
the electrochemical carbonylation of PhOH to DPC catalyzed by Pd (in situ SIt-Bu)
electrocatalyst. The effect of Au loading on the electrochemical carbonylation was
studied and 1.0, 5.0, 10.0, 15.0, and 25.0 wt% Au/graphene-3 were prepared.
Figure 4 shows (a) the electrochemical yields of DPC and CO2, (b) the stoichio-
metric yields of DPC and CO2 and their current efficiencies as a function of Au
loadings on the graphene-3 support. In the case of 0 wt% of Au, a small yield of
DPC was electrochemically formed at the graphene-3 ? VGCF anode. When the
Au loading on graphene-3 was increased from 1.0 to 10.0 wt%, the electrochemical
DPC yield linearly increased. The high electrochemical DPC yield of 46.9 lmol and
current efficiency of 70 % were obtained at 10.0 wt% loading. When the Au loading
was increased more than 10.0 wt%, the electrochemical DPC yield and current
efficiency did not increase. The stoichiometric yields of DPC and CO2 also did not
depend on the Au loadings. On the other hand, the electrochemical CO2 yields did
not depend on the Au loadings and were low values.
These experimental facts strongly suggest that smaller Au particles on carbon is
effective for the electrochemical DPC synthesis and promotes the oxidation of Pd
(in situ SIt-Bu) electrocatalyst. The stoichiometric reactions are independent of the
anodes. The 10.0 wt% Au loading is enough to obtain high yield and current
efficiency of DPC. Hereafter, the electrochemical carbonylation using the Au
(10.0 wt%)/graphene-3 ? VGCF anode was studied.
123

Electrosynthesis of diphenyl…
60
(b)
50
40
30
20
10
0
DPC
CO
2
60
50
40
30
20
10
0
80
60
40
20
0
(a)
DPC
CO
2
0
5
10
15
20
25
30
Au loading / wt%
Fig. 4 Effects of Au loading of the anode on electrochemical carbonylation of PhOH by Pd (in situ SIt-
Bu) electrocatalyst. a Electrochemical yields of DPC and CO2 and current efficiency of DPC and
b stoichiometric yields of DPC and CO2. Reaction conditions are the same as in Table 1, except for Au
loadings
As mentioned above, among 10.0 wt% Au/graphene-3 materials, smaller
crystalline size of Au was favor for the DPC formation. We tried to prepare a
smaller crystalline size of Au on the graphene-3 supported by using a chemical
reduction method. 10.0 wt% Au/graphene-3 was prepared using a NaBH4 reductant
[10]. This material was abbreviated as Au/graphene-3(NaBH4). The XRD spectrum
of Au/graphene-3(NaBH4) was shown in Fig. 2e. The diffraction peaks were
assigned to Au metal. The average crystalline size of the Au was 26 nm, which is a
half of the Au/graphene-3 reduced with H2, as abbreviated Au/graphene-3(H2).
Figure 5 shows TEM images of the 10 wt% Au/graphene-3(H2) and 10.0 wt%
Au/graphene-3(NaBH4). The EDS analysis in the TEM images showed that the
black spots correspond to Au. In both of the TEM images, we could observe
graphene sheets and numerous Au nanoparticles. Particle sizes observed in
Au/graphene-3(H2) were larger than that in Au/graphene-3(NaBH4). The distribu-
tion of Au particles in Au/graphene-3(H2) was form 20 to 140 nm, while that in
Au/graphene-3(NaBH4) was from 4 to 75 nm. The difference in average particle
size of Au in TEM images is in accordance with the average crystalline size of Au
evaluated from XRD spectra.
The results of electrochemical carbonylation of PhOH catalyzed by Pd (in situ
SIt-Bu) electrocatalyst at the Au/garaphene-3(NaBH4) ? VGCF anode were
123

R. Kanega et al.
Fig. 5 TEM images for a 10 wt% Au/graphene-3(H2) and b 10 wt% Au/graphene-3(NaBH4)
indicated at entry 8 in Table 1. The yield of DPC and the current efficiency of DPC
formation were slightly higher than that of the Au/graphene-3(H2) ? VGCF anode
at entry 7. In addition, the Au/graphene-3(NaBH4) ? VGCF anode was washed
with acetonitrile after electrolysis, and the washed Au/graphene-3(NaBH4) ? -
VGCF anode was reused for the electrochemical carbonylation using flesh
electrolysis solutions. As a result, the same DPC and CO2 yields were obtained at
the second run. The Au/graphene-3(NaBH4) ? VGCF anode can be reused for the
carbonylation and is stable. The advantage of the Au/graphene-3(NaBH4) ?
VGCF anode was small to compare with the Au/graphene-3(H2) ?VGCF anode at
1 mA galvanostatic electrolysis. To clarify reactivity of the Au/graphene-3(NaBH4)
anode, the electrochemical carbonylation of PhOH catalyzed by Pd (in situ SIt-Bu)
electrocatalyst was conducted at higher electrolysis currents of 2, 3, and 5 mA.
Figure 6 shows (a) electrochemical yield of DPC and CO2 and (b) current efficiency
of DPC and CO2 as functions of electrolysis current at the Au/graphene-
3(NaBH4) ? VGCF, Au/graphene-3(H2) ? VGCF and Au wire anodes. At 1 mA,
the electrochemical DPC yields of the Au/graphene-3(NaBH4) ? VGCF, Au/gra-
phene-3(H2) ? VGCF and Au wire anodes were 48.9, 46.8, and 44.4 lmol,
respectively. When electrolysis current was increased to 2, 3, and 5 mA, the
electrochemical DPC yield increased linearly in all the anodes, as shown in Fig. 6a.
The highest DPC yield of 118.3 lmol was obtained using the Au/graphene-
3(NaBH4) ? VGCF anode. The reactivates of the anodes were Au/graphene-
3(NaBH4) [ Au/graphene-3(H2) [ Au wire. The current efficiency of DPC forma-
tion at the Au/graphene-3(NaBH4) ? VGCF was very good at 1 mA; however,
current efficiency linearly decreased with the electrolysis current, as shown in
Fig. 6b. The current efficiency at the Au wire and Au/graphene-3(H2) ? VGCF
anodes also decreased with current. A higher current efficiency of 45 % was
obtained using the Au/graphene-3(NaBH4) ? VGCF anode at 5 mA. On the other
hand, the electrochemical CO2 yield and the current efficiency of CO2 did not
depend on the electrolysis currents. The sum of current efficiency of DPC and CO2
123

Electrosynthesis of diphenyl…
100
(b)
80
60
40
20
0
140
120
100
80
(a)
60
40
20
0
0
1
2
3
4
5
6
Electrolysis current / mA
Fig. 6 Effects of electrolysis current on electrochemical carbonylation of PhOH by Pd (in situ SIt-Bu)
electrocatalyst, a current efficiency of DPC and CO2 and b electrochemical yields of DPC and CO2 Au
wire (DPC: filled diamond, CO2: open diamond), Au/graphene-3(H2) ? VGCF (DPC: filled circle, CO2:
open circle) and Au/graphene-3 (NaBH4) ? VGCF (DPC: filled square, CO2: open square)
was 47 % at the Au/graphene-3(NaBH4) anode at 5 mA. Other byproducts could not
be detected. Use of the remaining current could not be revealed.
As described above, the current efficiency at 5 mA was not enough; however, the
Au/graphene-3(NaBH4) ? VGCF anode was most superior for the DPC formation
among the anodes tested. If smaller Au particles on graphene-3 are prepared, a
higher current efficiency and yield of DPC would be accomplished at high
electrolysis currents.
Conclusions
The electrochemical carbonylation of PhOH to DPC catalyzed by Pd (in situ SIt-Bu)
electrocatalyst using the Au/carbon anodes (carbon: AC, XC72, KBJD and
graphene-1, -2, -3) was studied at galvanostatic electrolysis conditions. The most
123

R. Kanega et al.
effective carbon support for the DPC formation was graphene-3, though the average
crystalline sizes of Au on AC, XC72, KBJD, graphene-3 were very similar
(54–57 nm). Effects of Au loading and reduction method of Au/graphene-3 on the
DPC formation were studied and 10.0 wt% Au/graphene (NaBH4) material was
superior. This material was characterized by XRD and TEM analyses and Au
crystalline size of 26 nm and small particles were observed. At sever electrolysis
condition of 5 mA, a fairly good current efficiency of 45 % was obtained for the
DPC formation. These data propose that graphene-3-supported Au particles of a few
nanometer material will be an effective anode, which accelerates electrochemical
oxidation of Pd0(in situ SIt-Bu) and achieves selective formation of DPC at higher
electrolysis currents.
References
1. N. Hersh, K.Y. Choi, J. Appl. Polym. Sci. 41, 1033 (1990)
2. J. Gong, X. Ma, S. Wang, Appl. Catal. A 316, 1 (2007)
3. J.E. Hallgren, G.M. Lucas, R.O. Mathews, J. Organomet. Chem. 204, 135 (1981)
4. A. Vavasori, L. Toniolo, J. Mol. Catal. A 139, 109 (1999)
5. H. Ishii, M. Goyal, M. Ueda, K. Takeuchi, M. Asai, Catal. Lett. 65, 57 (2000)
6. K. Okuyama, J. Sugiyama, R. Nagahata, M. Asai, M. Ueda, K. Takeuchi, J. Mol. Catal. A: Chem.
203, 21 (2003)
7. L. Ronchin, A. Vavasori, E. Aamdio, G. Cavinato, L. Toniolo, J. Mol. Catal. A: Chem. 298, 23
(2009)
8. M. Takagi, H. Miyagi, T. Yoneyama, Y. Ohgomori, J. Mol. Catal. A: Chem. 129, L1 (1998)
9. H.Y. Song, E.D. Park, J.S. Lee, J. Mol. Catal. A: Chem. 154, 243 (2000)
10. K. Okuyama, J. Sugiyama, R. Nagahata, M. Asai, M. Ueda, K. Takeuchi, Green Chem. 5, 563 (2003)
11. W. Xue, J.C. Zhang, Y.J. Wang, X.Q. Zhao, Catal. Commun. 6, 431 (2005)
12. G. Fan, T. Li, G. Li, Appl. Organometal. Chem. 20, 656 (2006)
13. G. Fan, J. Huang, Z. Li, T. Li, G. Li, J. Mol. Catal. A: Chem. 267, 34 (2007)
14. H. Guo, J. Lu, H. Wu, S. Xiao, J. Han, Adv. Mater. Res. 750, 1292 (2013)
15. T. Murayama, Y. Arai, T. Hayashi, I. Yamanaka, Chem. Lett. 39, 418 (2010)
16. T. Murayama, T. Hayashi, Y. Arai, I. Yamanaka, Electrochim. Acta 56, 2926 (2011)
17. T. Murayama, T. Hayashi, R. Kanega, I. Yamanaka, J. Phys. Chem. C 116, 10607 (2012)
18. R. Kanega, T. Hayashi, I. Yamanaka, ACS Catal. 3, 389 (2013)
19. R. Kanega, I. Yamanaka, Top. Catal. 57, 995 (2014)
20. M. Haruta, Cattech 6, 102 (2002)
21. T. Ishida, K. Kurod, N. Kinoshita, W. Minagawa, M. Haruta, J. Colloid Interface Sci. 323, 105 (2008)
123