Sulfur promoted Pt/SiO2 catalyzed cross-coupling of anilines and amines

Article abstract of DOI:10.1016/j.apcata.2011.12.019

Pt/SiO₂ (Pt = 5 wt%) catalysts with average Pt particle size of 3.3 and 6.8 nm and sulfur-loaded Pt/SiO₂ (S/Pt ratio = 0.1 and 0.13; Pt size = 5.2 and 5.5 nm), prepared by adding ammonium sulfate on Pt/SiO ₂ followed by H₂-reduction at 500 °C, are tested for mono-N-alkylation of aniline with di-iso-propylamine. The turnover frequency (TOF), defined as the reaction rate per number of surface Pt species, increases with sulfur loading. The catalyst with S/Pt ratio of 0.13 shows more than 5 times higher TOF than unmodified catalysts, and it acts as effective and recyclable catalyst for cross-coupling of various anilines and amines. Combined with kinetic results and characterizations, XAFS (X-ray absorption fine structure), TEM, and CO adsorption IR, a possible reason for the promotion effect of sulfur species (probably sulfidic species) is discussed.

Full text of DOI:10.1016/j.apcata.2011.12.019

Applied Catalysis A: General 417–418 (2012) 37–42
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Sulfur promoted Pt/SiO catalyzed cross-coupling of anilines and amines
2
a,∗
a
b
b
b
Ken-ichi Shimizu , Katsuya Shimura , Naoko Tamagawa , Masazumi Tamura , Atsushi Satsuma
a
Catalysis Research Center, Hokkaido University, N-21, W-10, Sapporo 001-0021, Japan
Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 October 2011
Received in revised form 5 December 2011
Accepted 11 December 2011
Available online 20 December 2011
Pt/SiO2 (Pt = 5 wt%) catalysts with average Pt particle size of 3.3 and 6.8 nm and sulfur-loaded Pt/SiO2
(
S/Pt ratio = 0.1 and 0.13; Pt size = 5.2 and 5.5 nm), prepared by adding ammonium sulfate on Pt/SiO2
◦
followed by H2-reduction at 500 C, are tested for mono-N-alkylation of aniline with di-iso-propylamine.
The turnover frequency (TOF), defined as the reaction rate per number of surface Pt species, increases with
sulfur loading. The catalyst with S/Pt ratio of 0.13 shows more than 5 times higher TOF than unmodified
catalysts, and it acts as effective and recyclable catalyst for cross-coupling of various anilines and amines.
Combined with kinetic results and characterizations, XAFS (X-ray absorption fine structure), TEM, and
CO adsorption IR, a possible reason for the promotion effect of sulfur species (probably sulfidic species)
is discussed.
Keywords:
Amines
Cross-coupling
Platinum
Sulfur
© 2011 Elsevier B.V. All rights reserved.
1
. Introduction
Pt catalyst has been the most industrially relevant and widely
attractive alternative method of alkylamine synthesis [15–29].
The reaction proceeds thorough a hydrogen-borrowing (hydro-
gen auto-transfer) mechanism [15–21]. The process begins with
the dehydrogenation of an alkylamine to the corresponding imine.
The imine undergoes addition of another nucleophilic amine and
elimination of ammonia to form an N-alkyl imine, which is hydro-
genated by in situ formed hydride species to the secondary amine
product. Ru [18,19] and Ir [20] complexes are successful catalytic
systems for selective amine cross-coupling of different amines,
leaving ammonia as the only by-product. From the environmen-
tal and economic viewpoints, it is preferable to accomplish the
selective cross-coupling reaction using reusable heterogeneous
catalysts. There are many reports of heterogeneous catalysis for
cross-coupling [16,17,21–24] or self-coupling [25–28] of amines.
However, previous examples of cross-coupling reactions suffer
from reusability [17], low turnover number (TON), and need of sto-
ichiometric amount of additives [21] or special reaction methods
(microwave heating [21,22], electrocatalysis [23], photocatalysis
investigated catalysts [1–13]. Recent reports demonstrated some
Pt-catalyzed green organic reactions such as selective oxidation
[
1–3], hydrogenation [4,5] and hydrogenolysis [6]. However, their
application to multi-step one-pot organic synthesis is limited. Sul-
fur is widely recognized as a poison of metallic Pt catalysts for
many reactions. Under reducing conditions the presence of sulfur
in general decreases the catalytic activity. There are a few reports of
promotional effects of sulfur species on Pt catalysts [7–13]. These
examples are based on the promotion effects of sulfate species on
the activity of Pt catalysts for hydroisomerization of alkanes and
combustion of hydrocarbons. For the former system, Hattori and
co-workers have established that sulfate species play an important
role in the formation of the molecular hydrogen-originated pro-
tonic acid site. For the latter system, the formation of acidic site at
the Pt/support/sulfate interface is suggested to be important [10].
However, to the best of our knowledge, positive effects of sulfur
species on Pt metal catalyzed multistep organic synthesis were not
reported.
[24]). Recently, we reported that Pt nanocluster-loaded ␥-Al O3
2
(Pt/Al O ) was effective for mono-N-alkylation of amines with dif-
2
3
ferent amines [29]. In this paper, we found that S-loaded Pt/SiO2
showed higher TOF (per number of surface Pt) than Pt/SiO2 and
Pt/Al O . Kinetic and structural studies are carried out to discuss a
Amines are intermediates and products of enormous impor-
tance for chemical and life science applications. In addition
to the well established Pd-catalyzed aminations of aryl halides
2
3
possible reason of the promotion effect of sulfur.
[
14] and the metal-catalyzed amination of alcohols [15,16], the
transition-metal-catalyzed alkylation of amines by amines is an
2. Experimental
Commercially available organic compounds (from Tokyo Chem-
∗ Corresponding author. Tel.: +81 11 706 9240; fax: +81 11 706 9163.
E-mail address: kshimizu@cat.hokudai.ac.jp (K.-i. Shimizu).
ical Industry or Kishida Chemical) were used without further
purification. The GC (Shimadzu GC-14B) and GC–MS (Shimadzu
0
926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.12.019

3
8
K.-i. Shimizu et al. / Applied Catalysis A: General 417–418 (2012) 37–42
Table 1
Table 2
List of catalysts.
Curve-fitting analysis of Pt L3-edge in situ EXAFS.
S/Pt (precursor)a
S/Pt (ICP)b
Tcal/ Cc
◦
D/nmd
Na
R/Åb
ꢀ/Åc
Rf/%d
Catalysts
Sample
Shell
Pt/SiO2-550
Pt/SiO2-600
SPt/SiO2-0.10
SPt/SiO2-0.13
0
0
1
5
–
–
0.10
0.13
550
600
–
3.3 ± 1.5
6.8 ± 3.0
5.2 ± 2.4
5.5 ± 3.2
SPt/SiO2-0.13
Pt/SiO2-550
Pt
Pt
9.6
10.6
2.74
2.75
0.088
0.083
2.6
0.9
a
Coordination numbers.
Bond distance.
Debye–Waller factor.
Residual factor.
–
b
c
a
S/Pt molar ratio in the catalyst precursors prepared by impregnation of
NH4)2SO4 to Pt/SiO2.
d
(
b
S/Pt molar ratio in the catalysts after calcination and H2-reduction of the pre-
cursors.
c
Temperatures of calcination.
Average particle size of Pt estimated by TEM.
In a typical catalytic test, SPt/SiO -0.13 (1 mol% Pt with respect
to aniline) was added to the mixture of aniline (1.0 mmol), di-iso-
propylamine (2.0 mmol) and o-xylene (2 mL) in a reaction vessel
2
d
equipped with a condenser and N was filled. The resulting mixture
2
GCMS-QP5000) analyses were carried out with a Rtx-65 capillary
column (Shimadzu) using nitrogen as the carrier gas.
was vigorously stirred under reflux condition (heating tempera-
◦
ture = 155 C) for 4 h. Products were identified with GC–MS and
SiO -supported Pt (Pt/SiO2 with Pt loading of 5 wt%) was pre-
2
1
H NMR [29]. Conversion of aniline and yields of products were
2
−1
pared by impregnating SiO2 (Q-10, 300 m g , supplied from
Fuji Silysia Chemical Ltd.) with an aqueous HNO3 solution of
determined by GC using n-dodecane as an internal standard.
Pt(NH ) (NO ) (Tanaka Kikinzoku), followed by evaporation to
3
2
3 2
◦
◦
dryness at 80 C, drying at 120 C for 12 h, calcination in air at
3. Results and discussion
◦
◦
5
00 C, and reduction in a flow of 100% H2 at 550 C for 10 min.
This sample is named Pt/SiO -550. The sample named Pt/SiO -600
3.1. Characterization
2
2
◦
was prepared by the similar method and reduced in H at 600 C for
2
1
0 min. Sulfur-loaded Pt/SiO2 catalysts were prepared by impreg-
Pt/SiO -550 (as a precursor of S-loaded catalysts), Pt/SiO -600,
2
2
nating Pt/SiO -550 with aqueous solution of (NH ) SO , followed
and SPt/SiO -x (x = 0.1, 0.13) were characterized by various spec-
2
4
2
4
2
◦
◦
by evaporation to dryness at 80 C, drying at 120 C for 12 h, and
troscopic methods. The S/Pt ratio of the catalyst was determined
by ICP analysis as listed in Table 1. XRD pattern of these samples
showed lines due to Pt metal. TEM measurements of these sam-
ples were carried out, and the particle size analysis was conducted
on 98–124 particles. The size distribution of Pt/SiO2 samples and
◦
reduction in a flow of 100% H at 500 C for 10 min. Table 1 includes
2
the relative amount of (NH ) SO in the solution to that of Pt atoms
4
2
4
in Pt/SiO and the S/Pt ratio of the catalyst after the H -reduction
2
2
◦
at 500 C determined by ICP analysis. The catalysts are designated
as SPt/SiO -x, where x is the S/Pt ratio. SPt/SiO -0.13 is used as a
SPt/SiO -0.13 are illustrated in Fig. 1. As listed in Table 1, the aver-
2
2
2
standard catalyst.
age particle size of SPt/SiO -x (x = 0.1, 0.13) and Pt/SiO -600 are
2
2
XRD patterns of the powdered catalysts were recorded with a
Rigaku MiniFlex II/AP diffractometer with Cu K␣ radiation. Trans-
mission electron microscopy (TEM) measurements were carried
out using a JEOL JEM-2100F TEM operated at 200 kV.
in a range 5.2–6.8 nm. Pt/SiO -550 has a relatively smaller Pt size
2
(3.3 nm).
3
Fig. 2A shows k -weighted in situ extended X-ray absorption
fine structure (EXAFS) data of SPt/SiO -0.13 acquired at room tem-
2
◦
In situ IR spectra were recorded at room temperature on a JASCO
FT/IR-620 equipped with a quartz IR cell connected to a conven-
tional flow reaction system. Samples were pressed into a 22 mg
of self-supporting wafer and mounted into the quartz IR cell with
CaF2 windows, and the spectrum was measured at room temper-
perature in a flow of He after H -reduction at 200 C. The Pt–Pt
2
coordination number and the distance are determined by curve-
fitting analysis and are listed in Table 2. The EXAFS consists of a
Pt–Pt contribution with coordination number of 9.6 at bond dis-
tance of 2.74 A˚ . These values are not markedly different from those
−
1
ature in He flow accumulating 15 scans at a resolution of 4 cm
.
of Pt/SiO -550: Pt–Pt coordination number of 10.6 at bond dis-
2
For the CO adsorption IR experiments, a reference spectrum of the
catalyst wafer in He was subtracted from each spectrum. Prior to
tance of 2.75 A˚ . This indicates that the presence of sulfur species on
Pt/SiO does not change the bulk structure of metallic Pt. The EXAFS
2
each experiment the catalyst disk was heated in H (2%)/He flow
result showed no Pt–S bond in the SPt/SiO -0.13 sample. In the IR
2
2
3
−1
◦
(
100 cm min ) at 500 C for 10 min, followed by cooling to room
spectrum of the unreduced precursor, (NH ) SO -loaded Pt/SiO -
4 2 4 2
−
1
temperature under He flow. Then, the catalyst was exposed to a
flow of CO(0.9%)/He for 180 s.
550 with S/Pt ratio of 5, a band due to sulfate species (1420 cm
was observed (result not shown). This band was not observed for
the H -reduced sample, SPt/SiO -0.13. Taking into account the fact
)
Pt L -edge in situ XAFS measurement was carried out at BL01B1
3
2
2
of SPring-8 (Hyogo, Japan). The storage ring energy was operated
at 8 GeV with a typical current of 100 mA. A self-supported wafer
form (pressed pellet) of the pre-reduced Pt catalyst with 10 mm
that the catalyst exhibits the S/Pt ratio of 0.13 (ICP result in Table 1),
it is reasonable to assume that sulfidic sulfur species are present on
the catalyst and some of them may present on the surface of Pt.
As shown in Table 2, the coordination number for the Pt–Pt
bond in Pt/SiO -550 (10.6) was larger than that of SPt/SiO -0.13
diameter was placed in a quartz in situ cell in a flow of 100% H
2
3
−1
◦
(
100 cm min ) for 30 min at 200 C under atmospheric pressure,
2
2
◦
and the sample was cooled to 40 C under a flow of He, then the
spectra were recorded in situ. The analyses of the extended X-ray
absorption fine structure (EXAFS) and X-ray absorption near-edge
structures (XANES) were performed using the REX version 2.5 pro-
(9.6). On the other hand, the Pt particle size of Pt/SiO -550 (3.3 nm)
2
was smaller than that of SPt/SiO -0.13 (5.2 nm). Assuming that the
2
shape of Pt particle does not depend on the presence of sulfur, it is
likely that EXAFS data is not consistent with the average size of Pt
particles measured by TEM. This inconsistency might be explained
3
gram (RIGAKU). The Fourier transformation of the k -weighted
EXAFS from k space to R space was carried out over the k range
as follows. Some of the sulfur species in SPt/SiO -0.13 interact
strongly with Pt surface, which results in an increased disorder in
the local structure of the Pt metals.
2
−
1
3
–15 A˚
to obtain a radial distribution function. The inversely
Fourier filtered data (in the R range of 1.5–3.3 A˚ ) were analyzed with
−
1
a usual curve fitting method in the k range of 3.3–14.7 A˚ using the
Fig. 2B shows in situ X-ray absorption near-edge structures
empirical phase shift and amplitude functions for Pt–Pt and Pt–O
(XANES) for SPt/SiO -0.13. It is clear that the XANES spectrum
2
shells extracted from the data for Pt foil and PtO , respectively.
of SPt/SiO -0.13 is nearly identical to that of Pt/SiO -550, which
2
2
2

K.-i. Shimizu et al. / Applied Catalysis A: General 417–418 (2012) 37–42
39
Pt/SiO -600
SPt/SiO -0.13
Pt/SiO -550
2
2
2
3
2
1
0
0
0
0
0
5
10
0
5
10
0
5
10
15
D / nm
D / nm
D / nm
Fig. 1. Particle size distribution of from TEM analysis.
A
B
2.0
Pt/SiO -0.13
2
Pt/SiO -550
2
0
1
2
3
4
5
6
11550
11560
11570
R / Å
X-ray energy/eV
◦
◦
Fig. 2. In situ Pt L3-edge (A) EXAFS and (B) XANES spectra of (dashed lines) Pt/SiO2-550 and (solid lines) SPt/SiO2-0.13 recorded under He at 40 C after flowing H2 at 200
C
for 10 min.
indicates that the presence of S on Pt/SiO2 does not change the
bulk electronic state of metallic Pt.
reduction of 4. The S-doped catalyst, SPt/SiO -0.13, gave 100% con-
2
version of 1, 98% yield of the desired amine 3 and low yield of the
byproduct 4 (2%) after 4 h (entry 1 in Table 3), corresponding to
XANES reflects the average oxidation states of Pt located at bulk
and surface of metal particles. IR spectroscopy with CO as a probe
molecule allows monitoring of the changes in the electronic states
of surface Pt. Fig. 3 shows IR spectra of CO adsorbed on the Pt cata-
lysts in a region characteristic to linearly coordinated CO on metallic
−
1
the turnover frequency (TOF) of 24.5 h based on the total num-
ber of Pt atoms in the catalyst. This value is higher than that of
−1
Pt (2100–2000 cm ). It is widely recognized that the wavenumber
of the band due to the linear CO adspecies increases with an increase
in the electron deficiency of the metal. The result showed that the
addition of S did not markedly change the wavenumber of the max-
−
1
imum intensity; the wavenumber for SPt/SiO -0.13 (2085 cm
)
2
−
1
is in between those of Pt/SiO -550 (2090 cm ) and Pt/SiO -600
2078 cm ). This suggests that the addition of S does not change
2
2
−1
(
the surface electronic state of Pt.
3.2. Catalytic and kinetic studies
N-Alkylation of aniline (1) with
2 equivalent of di-iso-
propylamine (2), iPr NH, in N2 atmosphere was chosen as a test
2100
2000
2
reaction of cross-coupling reaction of amines. Fig. 4 shows changes
in the yields of the unreacted aniline 1, an imine intermedi-
ate (isopropylidene-phenylamine 4) and N-isopropylaniline (3)
as a desired hydrogenated product, which can be produced by
Wavenumber /cm-1
Fig. 3. IR spectra of CO adsorbed on (dashed line) Pt/SiO2-550, (solid line) SPt/SiO2-
0.13 and (dotted line) Pt/SiO2-600.

4
0
K.-i. Shimizu et al. / Applied Catalysis A: General 417–418 (2012) 37–42
Pt/SiO -550
Pt/SiO -600
SPt/SiO -0.13
2
2
2
100
80
60
40
20
0
0
1
2
3
0
1
2
3
0
1
2
3
4
Time / h
Time / h
Time / h
Fig. 4. Yields of (ꢀ) unreacted 1, (ꢀ) N-isopropylaniline 3 and (᭹) isopropylidene-phenylamine 4 for the reaction of aniline with iPr2NH vs. reaction time.
homogeneous Ir catalyst (TOF = 9.8 h−1) [20] for the same reaction
at the same temperature. This demonstrates a highly efficient fea-
ture of the present catalytic system. In contrast, the unmodified
catalysts (Pt/SiO -550, Pt/SiO -600) showed lower 1 conversion
To study the scope and limitation of the present reaction by
SPt/SiO2-0.13, the alkylation of anilines with various aliphatic
amines were tested (Table 3). Secondary (entries 1 and 3) and
primary amines (entries 4–6) acted as effective amine donor.
For example, the reaction of aniline 1 with a secondary amine,
di-sec-butylamine (entry 3), lead to the formation of the cor-
responding N-alkylated amine in high yield (95%). However,
the reaction of 1 with a primary amine, iPrNH2 (entry 6)
gave lower yield (49%) than the standard reaction of 1 with
iPr2NH (entry 1). The amination of the aniline derivative with a
2
2
and 3 yield than SPt/SiO -0.13 but higher yield of the imine inter-
2
mediate 4. After the reaction, the SPt/SiO -0.13 catalyst was easily
2
separated from the reaction mixture by centrifugation. The sepa-
rated catalyst was washed with acetone (5 mL), followed by drying
◦
◦
at 200 C for 1 h, and by reducing in H2 at 500 C for 10 min. Then,
the reused catalyst showed 90% yield of 3 (entry 2 in Table 3).
Table 3
N-Alkylation of aniline with various amines.
H
NH
2
+
RNH
NH
2
,
SPt/SiO -0.13 (1mol%)
2
N
R
2
R
o-xylene (2 mL)
, reflux, 4 h
X
X
1
mmol
2 mmol
Entry
Amine substrate
Amine donor
Product
Yield/%a
H
N
1
N
H
98
90
NH2
2b
H
N
NH2
N
H
3
4
5
6
95
97
75
49
H
N
NH2
NH2
NH2
NH2
H
N
NH2
H
N
NH2
NH2
H N
2
HN
7
87
a
Yields of product determined by GC are based on aniline.
Reaction by the reused catalyst after entry 1.
b

K.-i. Shimizu et al. / Applied Catalysis A: General 417–418 (2012) 37–42
41
3
2
1
00
00
00
N
N
H
Pt
3
4
2
Pt-H
N
N
2
'
NH2
+
NH3
NH2
1
0
0.05
0.1
0.15
Scheme 1. Proposed mechanism of Pt-catalyzed alkylation of aniline with iPr2NH.
S/Pt ratio
sterically hindered substituent at ortho position was also successful
Fig. 6. (ꢀ) TOF based on the number of surface Pt atom vs. S/Pt ratio in Pt/SiO2-600,
SPt/SiO2-0.10, and SPt/SiO2-0.13. Closed triangle (ꢁ) denotes TOF for Pt/SiO2-550.
(
entry 7).
As previously postulated in the literature [17–20], it is most
probable that the amine cross-coupling reaction proceeds through
the hydrogen borrowing pathway (Scheme 1), in which the reac-
aniline (Fig. 5B), which suggests that iPr NH is involved in a rate-
2
tion is initiated by a temporary removal of hydrogen from iPr NH 2
to generate imine 2 and Pt–H species. The following kinetic results
give further evidences on the mechanism of the Pt-catalyzed N-
limiting step and aniline is not involved in the rate-limiting step for
both catalysts. The results also rule out a possibility that hydrogena-
tion of imine 4 by Pt–H species is the rate-limiting step. The result
in Fig. 5A shows that the addition of S decreases the reaction orders
2
ꢁ
alkylation of aniline 1 with iPr NH 2. As shown in Fig. 4, a typical
2
time-conversion profile of the consecutive reaction was observed
with respect to iPr NH. This indicates that sulfur species promote
2
for the reaction by SPt/SiO -0.13; the imine intermediate 4, formed
the rate-limiting iPr NH dehydrogenation step.
2
2
at an initial period, was consumed, and then the yield of the
hydrogenated product 3 increased with time. This indicates that
N-isopropylaniline 3 is produced through a consecutive pathway
via the N-alkylimine 4. Since the reaction was performed under N2,
it is reasonable to assume that imine 4 is hydrogenated by hydrogen
To quantify the effect of S-addition on the activity, the rate of
3 formation was measured under the condition where conversion
of 1 was below 40%, and TOF per surface Pt species was calculated
using the number of surface Pt atom (from TEM results) and the
reaction rate. The TOF is plotted as a function of the S/Pt ratio in
species formed by the dehydrogenation of iPr NH. iPrNH2 formed
Fig. 6. For the SPt/SiO -x (x = 0.1, 0.13) catalysts with different S/Pt
2
2
as a byproduct could be dehydrogenated by Pt sites and could act
ratio but with the same Pt loading (5 wt%) and similar Pt particle
as an alkylating agent. However, considering the result that iPrNH2
size (Table 1), TOF increased with S/Pt ratio. SPt/SiO -0.13 showed
2
shows lower reactivity than iPr NH (Table 3), the reaction of 1
with iPrNH2 should be the minor root in the reaction of 1 with
more than 5 times higher TOF than the undoped Pt/SiO2 cata-
2
−
lysts. It is important to note that the TOF SPt/SiO -0.13 (256 h ) is
2
1
−
1
iPr NH. The effect of reactant concentration on the activity was
higher than that of Pt/Al O3 (101 h ) shown in our recent report
2
2
tested for SPt/SiO -0.13 and Pt/SiO -550. In Fig. 5, the reaction rates
[29]. Combined with the XANES and EXAFS results that the addi-
tion of S does not essentially change the structure and electronic
state Pt species, a possible reason of the enhanced catalytic activ-
2
2
are plotted as a function of the initial concentration of iPr NH and
2
aniline. The rate dependence on the iPr NH concentration (Fig. 5A)
2
showed the reaction order (n) of 0.91 and 2.0 for SPt/SiO -0.13
ity may be a cooperation of sulfur and Pt species in the iPr NH
2
2
and Pt/SiO -550, respectively. The reaction orders with respect to
dehydrogenation step as the rate-limiting step of the catalytic
cycle.
2
iPr NH (Fig. 5A) are higher than the reaction orders with respect to
2
A
B
3
3
2
n= 0.43
n= 0.16
n= 0.91
2
1
1
0
0
n= 2.0
-
1
-1
-
2
-1.5
-1
-0.5
-2
-1.5
-1
-0.5
ln (CiPr2NH / M)
ln (Caniline / M)
Fig. 5. Formation rate of 3 (as a function of the concentration of (A) iPr2NH and (B) aniline for the reaction of aniline with iPr2NH by (ꢂ, dashed lines) Pt/SiO2-550 and (ꢀ,
solid lines) SPt/SiO2-0.13.

4
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K.-i. Shimizu et al. / Applied Catalysis A: General 417–418 (2012) 37–42
4
. Conclusions
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Brijoux, H. Bönnemann, G. Schmid, Appl. Organomet. Chem. 15 (2001) 178–196.
(
[
Sulfur-promoted 5 wt% Pt/SiO2 catalysts with similar Pt parti-
cle size but with different S loading (S/Pt ratio of 0, 0.1, 0.13) were
[5] S. Ikeda, S. Ishino, T. Haranda, N. Okamoto, T. Sakata, H. Mori, S. Kuwabata, T.
Torimoto, M. Matsumura, Angew. Chem. Int. Ed. 45 (2006) 7063–7066.
prepared by a loading of ammonium sulfate on Pt/SiO , followed
2
[
6] J.N. Kuhn, W.Y. Huang, C.K. Tsung, Y.W. Zhang, G.A. Somorjai, J. Am. Chem. Soc.
30 (2008) 14026–14027.
by H -reduction. It was found that the catalytic activity (TOF per
2
1
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Acknowledgments
This work was supported by the Japanese Ministry of Education,
Culture, Sports, Science and Technology via Grant-in-Aids for Scien-
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The X-ray absorption experiment was performed with the approval
of the Japan Synchrotron Radiation Research Institute (Proposal No.
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