Pt nanoparticle supported on nanocrystalline CeO2: Highly selective catalyst for upgradation of phenolic derivatives present in bio-oil

Article abstract of DOI:10.1039/c4ta04542d

Pt nanoparticle supported on nanocrystalline CeO₂ was prepared, and it was found that the catalyst can selectively hydrogenate phenolic derivatives present in bio-oil. The catalyst was characterized by XRD, XPS, ICP-AES, EXAFS, SEM and TEM. TEM micrograms confirm the presence of very small Pt nanoparticles supported on nanocrystalline CeO₂. The catalyst was found to be very effective in liquid phase hydrogenation of phenol and phenolic compounds present in bio-oil in the presence of molecular H₂. The synergy between the surface and very small Pt particles on the nanocrystalline CeO₂ plays the most vital role towards the extremely high catalytic activity of the catalyst. The reusability of the catalyst was tested, and it was found that the catalyst does not exhibit any significant change in its catalytic activity even after five reuses. The catalyst showed ～100% conversion with very high selectivity after 3 h in phenol conversions of 100% with >98% cyclohexanol selectivity achieved after 3 h of reaction at 100 °C in aqueous medium.

Full text of DOI:10.1039/c4ta04542d

Journal of
Materials Chemistry A
View Article Online
View Journal | View Issue
PAPER
Pt nanoparticle supported on nanocrystalline
CeO2: highly selective catalyst for upgradation of
Cite this: J. Mater. Chem. A, 2014, 2,
phenolic derivatives present in bio-oil†
18398
Bipul Sarkar,a Chandrashekar Pendem,a L. N. Sivakumar Konathala,a Takehiko Sasakib
a
*
and Rajaram Bal
Pt nanoparticle supported on nanocrystalline CeO2 was prepared, and it was found that the catalyst can
selectively hydrogenate phenolic derivatives present in bio-oil. The catalyst was characterized by XRD,
XPS, ICP-AES, EXAFS, SEM and TEM. TEM micrograms confirm the presence of very small Pt
nanoparticles supported on nanocrystalline CeO2. The catalyst was found to be very effective in liquid
phase hydrogenation of phenol and phenolic compounds present in bio-oil in the presence of molecular
H2. The synergy between the surface and very small Pt particles on the nanocrystalline CeO2 plays the
most vital role towards the extremely high catalytic activity of the catalyst. The reusability of the catalyst
was tested, and it was found that the catalyst does not exhibit any significant change in its catalytic
activity even after five reuses. The catalyst showed ꢀ100% conversion with very high selectivity after 3 h
in phenol conversions of 100% with >98% cyclohexanol selectivity achieved after 3 h of reaction at
100 ꢁC in aqueous medium.
Received 1st September 2014
Accepted 10th September 2014
DOI: 10.1039/c4ta04542d
www.rsc.org/MaterialsA
300 ꢁC),6 and the catalyst suffers deactivation due to rapid
coking on the metal surface of the catalyst. Furthermore, the
Introduction
process cost can be overcome by liquid phase hydrogenation of
phenol and its derivatives. However, current liquid phase
hydrogenation of phenol and phenolic derivatives requires the
use of an organic solvent, e.g. dichloromethane, which has
associated health hazards.7 The prospective use of water as a
solvent not only benets the environment, but is also
economically viable. For practical use, the catalyst should have
good mechanical stability to resist the leaching of active metals
during the operation in aqueous medium. Lercher et al. devel-
oped a carbon supported Pd catalyst and tested it in combina-
tion with the mineral acid H3PO4 for the hydrogenation of
phenol and phenolic compounds present in bio-oil.2b However,
they used expensive metal Pd with very high loading in the
presence of extremely high H2 pressure. Furthermore, the use of
H3PO4 makes the process hazardous and environmentally
unfriendly. Thus, the development of the highly active envi-
ronmentally friendly catalyst still remains a major challenge for
researchers. Among the most conventional and common
synthesis routes, template assisted methods have been specially
highlighted as an alternate route to prepare nanostructure
materials.8 In recent years, signicant efforts have been made in
the controlled synthesis of supported metal nanoparticles, but
most of the preparation methods are energy intensive, require
substantial heat treatment and produce large particles.9
Signicant challenges in commercializing these materials still
exist due to their low synthetic yields, costly production and
unreliable material applications. Our group has developed a
Bio-oil is a promising renewable energy carrier, which is basi-
cally made up of components from cellulose and lignin.1
However, in order to be used as a suitable fuel, it needs to be
hydrogenated to boost the H/C ratio, octane number and calo-
ric value. Although lignin-derived phenolic compounds
account for 25–30% of the raw bio-oil,2 they have an inferior
oxygen content.3 Hence, the hydrogenation of phenol and
phenolic derivatives has been paid considerable attention for
over a couple of years. Moreover, owing to their selective
hydrogenation activity, the supported metal nanoparticles
catalysts are of great commercial importance for the modern
chemical and petroleum industry.4 Traditional Pd supported on
Al2O3, MgO, SiO2, Ta2O5, CeO2, ZrO2, La2O3, hydrotalcite, TiO2
or C was found to be an effective catalyst for the hydrogenation
of phenol.5 However, the gas phase hydrogenation of the
phenolic compound requires a high reaction temperature (150–
aCatalytic Conversion & Processes Division, CSIR-Indian Institute of Petroleum,
Dehradun 248005, India. E-mail: raja@iip.res.in; Fax: +91 135 2660202; Tel: +91
135 2525797
bDepartment of Complexity Science and Engineering, Graduate School of Frontier
Sciences, The University of Tokyo, Kashiwanoha, Kashiwa-shi, Chiba 277-8561,
Japan. E-mail: takehiko@k.u-tokyo.ac.jp
† Electronic supplementary information (ESI) available: SEM micrograms
commercial CeO2 and 2%Pt–CeO2 catalyst along with O, Pt and Ce elemental
mapping, EDAX, XPS, EXAFS of the catalyst and inuence of Pt loading,
reaction temperature and TOF calculation were available in the ESI. See DOI:
10.1039/c4ta04542d
18398 | J. Mater. Chem. A, 2014, 2, 18398–18404
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry A
day under autogenous pressure. The material was washed with
water and dried at 100 ꢁC overnight. The nal material was
ꢁ
calcined in air at 550 C for 6 h.
Supported Pt catalyst was prepared as follows: 0.197 g
Pt(NH3)4(NO3)2 was dissolved with 50 ml H2O containing
0.205 g CTAB, followed by the addition of 50 ml ethanol con-
taining 5 g of previously prepared CeO2 powder. The mixture
was stirred for 2 h at room temperature, and then it was kept at
90 ꢁC for complete evaporation. Finally, the mixture was dried at
Scheme
hydrogenation.
1 Schematic of probable reaction pathway for phenol
ꢁ
ꢁ
100 C and calcined at 550 C in air for 6 h. The as-prepared
catalyst was denoted as %Pt (%wt)-CeO2. For reference purposes,
the catalyst was also prepared via an impregnation method using
synthesis strategy for the preparation of nanostructure
materials by a hydrothermal method in the presence of a
surfactant.10
commercial CeO2 and denoted as %Pt (%wt)-CeO2comm
.
Cyclohexanol and its derivatives are one of the major raw
materials for the production of polyamide bers and plastics
such as nylon-6 and nylon-66.11 Commercially, the production
of cyclohexanol is carried out by two major processes: oxidation
of cyclohexane over Co-based homogeneous catalyst12 and
hydrogenation of phenol over Ni-based heterogeneous cata-
lyst.13 The former process suffers from low energy efficacy,
indicating a poor conversion with production of plenty of by-
products,14 whereas the latter process suffers from rapid coke
formation over the metal surface.15 Herein, we report the
preparation of Pt nanoparticles with size between 1 and 3 nm,
which are supported on nanocrystalline CeO2 for the selective
hydrogenation of phenol (Scheme 1) and its derivatives present
in bio-oil. A conversion of >99% with very high cyclic alcohol
Catalyst characterization
Powder X-ray diffraction (XRD) measurements were performed
with a Bruker D8 advance X-ray diffractometer with a Cu Ka
radiation (40 kV and 30 mA) in the 2q range of 5ꢁ–60ꢁ. The SEM
images are obtained on a FEI Quanta 200 F, using ETD detector
with an acceleration tension of 10 or 30 kV. All the samples were
analysed by spreading them on a carbon tape and coated with
gold to increase the electrical conductivity. Energy dispersive X-
ray spectroscopy (EDX) was used in connection with SEM for
elemental analysis. The elemental mapping was also collected
with the same spectrophotometer. The morphology, lattice
fringes and crystal boundaries of the samples were examined
using a JEOL JEM 2100 high-resolution transmission electron
microscope (HRTEM). Samples were mounted by dispersing on
ethanol on a lacey carbon Formvar coated Cu grid. Energy
dispersive X-ray spectroscopy (EDX) and elemental mapping
were used in connection with HRTEM for the elemental analysis
and e-mapping. The BET surface area and the nitrogen
adsorption–desorption apparatus (BELSORP-mini II, Bel Japan
Inc.) were employed to characterize the pore properties of the
samples. Before nitrogen adsorption–desorption measure-
ments and BET surface area measurements, the sample was
degassed at 200 ꢁC under vacuum. X-Ray photoelectron spectra
(XPS) of the catalysts were obtained with a Thermo Scientic K-
Alpha X-ray photoelectron equipped with Mg Ka radiation. The
C 1s peak at 284.8 eV was used as a calibration peak. Extended
X-ray absorption ne structure spectroscopy (XAFS) measure-
ments of the Pt-K edge were carried out at the High Energy
Accelerator Research Organization (KEK-IMMS-PF), Tsukuba,
Japan. The measurement was made at transition mode, and
spectra were taken at BL-7C and BL-9C. The electron storage
ring was operated at 2.5 GeV and 450 mA, and the synchrotron
radiation from the storage ring was monochromatized by a Si
(111) channel cut crystal. Ionized chambers, which were used as
detectors for incident X-ray (Io) and transmitted X-ray (I), were
lled with N2 mixture gas. The angle of the monochromators
was calibrated with Cu foil.
ꢁ
selectivity was achieved at 100 C in the presence of molecular
hydrogen in aqueous medium.
Experimental
Materials
Cerium nitrate hexahydrate (Ce(NO3)3$6H2O), tetraammine
platinum(II) nitrate [Pt(NH3)4](NO3)2], commercial CeO2, and
poly (diallyldimethylammonium chloride) solution (PDADMAC)
were purchased from Sigma-Aldrich Co. Ethanol, cetyl-
trimethylammonium bromide (CTAB), and NH3 solution were
purchased from Merck KGaA, Darmstadt, Germany. All the
chemicals were used without further purication. Doubly
distilled water was prepared with a BOROSIL® water distillation
unit.
Catalyst preparation
Preparation of nanocrystalline CeO2 was carried out in the
presence of cationic copolymer poly (diallyldimethyl-
ammonium chloride), i.e. [PDADMAC]. In a typical preparation
method, 1.7 g polyDADMAC was mixed with 22.5 ml doubly
distilled water under vigorous stirring. Then, a solution con-
taining 21.9 g Ce(NO3)3$6H2O dissolved in 20 ml water was
added slowly to this solution and stirred for 30 min. The nal
pH of the resulting solution was adjusted to ꢀ9 by the dropwise
Hydrogenation of phenol and phenolic derivatives
addition of ammonia solution, and the mixture was aged for Hydrogenation of phenol and its derivatives was carried out in a
24 h. Finally, the container was transferred into a Teon-lined 100 ml high pressure (Parr Instrument Company, USA) reactor
ꢁ
stainless autoclave for hydrothermal treatment at 180 C for 1 at various temperatures. The reactor was equipped with a
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 18398–18404 | 18399

View Article Online
Journal of Materials Chemistry A
Paper
mechanical stirrer, and a programmable PID controller was
used to control the temperature. 100 mg catalyst (reduced at
550 ꢁC with 10% H2 before each reaction) were taken with 20 ml
H2O containing 10 mmol (0.92 g) phenol/phenolic derivative.
The reactor is pressurized with H2, and the heating was started
with 500 rpm rotation. The catalyst was separated by centrifu-
gation and the reaction products were identied by GC-MS (HP
5890 GC coupled with 5972 MSD). The identied product was
analysed in a Thermo GC 700 tted with an HP-5 (30 m Â
0.28 nm i.d., 0.25 mm lm thickness) capillary column and an
FID detector.
Results and discussion
Catalyst characterization
Fig. 1 shows the X-ray diffraction (XRD) pattern of the Pt–CeO2
catalyst. All the peaks exhibit the face-centered-cubic CeO2
(JCPDS no. 43-1002). No XRD peak attributed to PtO was
observed for 2%Pt–CeO2 catalyst, which is possibly due to the
highly dispersed Pt species in sub-nanometre range and low
loading Pt. However, the XRD of freshly reduced (with 5% H2 for
1 h at 300 ꢁC) 2%Pt–CeO2 catalyst shows XRD peaks at 2q values
of 39.8ꢁ and 46.3ꢁ are assigned to the crystal faces of Pt (111)
and (200), respectively, which agrees well with the JCPDS no. 05-
0681. The Scherrer equation was used by taking full width half
maxima of the line boarding, corresponding to the diffraction
angle of (111) plane of Pt (Fig. S1, ESI†); moreover, a mean
crystallite size of 2.2 nm was observed, which matched well with
the average size obtained from TEM data. The BET surface area
Fig. 2 (A) Appearance of the Pt–CeO2 catalyst in SEM; (B–D) TEM
images of the catalyst; (E) partial size distribution histogram of (C); and
(F) selected area diffraction (SAD) pattern of the catalyst.
estimated by nitrogen adsorption of 2%Pt–CeO2 was 70 m2 gÀ1
.
The morphologies of the Pt–CeO2 catalysts were investigated by
eld emission scanning electron microscopy (FESEM). The
representative SEM images of the catalyst are shown in Fig. 2A
and S2 (in ESI†). Small spherical particles of highly ordered
nanocrystalline CeO2 can be seen with size between 15 and 30
nm. The presence of Pt on nanocrystalline CeO2 support was
Fig. 1 XRD pattern of as-prepared CeO2 (in black), 2%Pt–CeO2 (in
blue) and reduced 2%Pt–CeO2 catalyst (in red); the corresponding
peaks were identified using JCPDS card no-43-1002 (for CeO2) and Fig. 3 HRTEM images of the Pt–CeO2 catalyst showing crystal faces
05-0681 (for Pt).
of Pt (200) and CeO2 (110).
18400 | J. Mater. Chem. A, 2014, 2, 18398–18404
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry A
conrmed by EDAX (Fig. S3 and S4†). The corresponding
elemental mapping of the catalyst reveals a homogeneous
distribution of Pt on the CeO2 support (Fig. S3 and S4†). The
TEM images of the 2%Pt–CeO2 catalyst is shown in Fig. 2B–D.
The Pt particle size distribution histogram shown in Fig. 2E
indicates the formation of 1–3 nm Pt particles on CeO2
supports. The HRTEM image (Fig. 2D and 3) showed the high
degree of (220) orientation of Pt nanoparticles, which was
further conrmed by the corresponding SAED pattern in Fig. 2F.
˚
The lattice fringe with a d-spacing of 1.9 A corresponds to the
˚
(200) plane of Pt, and the distance of 2.9 A corresponds to the
(110) plane of CeO2 (Fig. 3). Fig. 4 shows the XPS binding
energies of the fresh and spent catalyst where A represents the
spectra of fresh catalyst and B for the spent catalyst. The Ce 3d
peaks at 882.2 (Ce 3d5/2) eV and 900.5 (Ce 3d3/2) eV shown in
Fig. S5 (ESI†) conrm the presence of Ce4+
.
The Pt 4f7/2
16
binding energy values of 75.0 eV conrm the presence of Pt2+
species before the reaction, and the binding energy of 71.2 eV
conrms the presence of metallic Pt aer the reaction.16b,17
Fig. 4 X-ray photoelectron spectra of Pt 4f in (A) fresh unreduced
catalyst and (B) spent catalyst.
Table 1 Summary of the EXAFS fitting results for Pt–CeO2 catalystsa
R (10À1 nm)
CN
DW (nm2)
Path
Debye temp (K)
DE0 (eV)
Rf (%)
Fresh
Spent (aer 3 h)
1.971
2.768
3.80
8.97
3.100 Â 10À4
Pt–O
Pt–Pt
286.0 Æ 6.0
286.6 Æ 8.3
7.55
6.66
1.76
2.20
4.182 Â 10À3
a
Fitting was achieved with respect to Pt–O and Pt–Pt paths, which were prepared by ATOMS program and Pt crystal structure. These two simple
paths such as Pt–O and Pt–Pt, the sole use of Pt crystal paths, or the PtO crystal structure were not enough for good tting. The former Pt–O
path can be tted as 0.1971–0.2768 nm, which can be attributed to the distance of Pt–O of the monatomically dispersed Pt species. The crystal
size of Pt is considered as small because the inclusion of more distant paths does not improve the llings.
Table 2 Activities of the different CeO2 and Pt–CeO2 catalysts on phenol hydrogenationa
Condition
cs
Sl no
Catalyst
T (ꢁC)
P (bar)
T (h)
cC
cF
1
2
3
4
5
6
7
8
CeO2
100
100
100
100
100
100
100
100
100
100
80
30
30
30
30
30
30
30
30
30
30
50
1
3
3
3
3
3
3
1.5
3
3
3
3
12
4
16
20
—
24
20
61
—
—
—
23
2%Ni–CeO2
2%Re–CeO2
2%Pd–CeO2
2%Rh–CeO2
2%Pt–CeO2
87.2
51.2
39.1
51.5
98.6
94.6
63.2
98.2
67.6
ꢀ92.0
ꢀ1.0
ꢀ1.0
ꢀ1.0
100
12.8
11.6
60.9
11.2
1.4
5.4
36.8
1.8
32.4
ꢀ8.0
ꢀ99.0
ꢀ99.0
ꢀ99.0
0
62
108
41
325
650
39
318
318
92
1.3
10
1.3
24
100
100
12
98
7
ꢀ26
ꢀ78
ꢀ99
ꢀ99
100
b
2%Pt–CeO2
2%Pt–CeO2
c
d
9
2%Pt–CeO2
10
11
12
13
14
15
2%Pt–CeOi2mp
5%Pd–C*
*
Pd–AlCl3
Pd@mpg-C3N4
45
100
90
*
1
1
10
*,e
Pd NPs
10%Pd@C*
100
1
a
Reaction conditions: 0.94 g phenol (10 mmol), 20 ml H2O, 0.1 g reduced catalyst. *Data taken from ref. 2b, 7a, 18, 19a and 19b; cc: conversion of
phenol; cs: product selectivity and cF: turnover frequency (TOF) in hÀ1
.
Catalyst amount increased to 0.2 g. c 2%Pt on commercial CeO2. d Aer ve
b
reuses. e Homogeneous catalyst.
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 18398–18404 | 18401

View Article Online
Journal of Materials Chemistry A
Paper
Table 3 Activities of Pt–CeO2 on different phenolic derivatives of bio-
Detailed structural parameters of the Pt species were
obtained by Pt LIII-edge EXAFS analysis. Pt LIII-edge EXAFS
spectra are shown in Fig. S6 (in ESI†). The curve tting results
are summarized in Table 1. For the fresh catalyst, the presence
oila
cs
˚
Sl No Catalyst
Substrate
cC
C–OH
C]O
cF
of a Pt–O bond length of 1.971 A with coordination number (CN)
3.80 indicates the presence of cationic Pt species. The structural
parameters determined by Pt LIII-edge EXAFS spectra of Pt–CeO2
catalyst aer the hydrogenation reaction shows the Pt–Pt bond
1
2
2%Pt–CeO2
100
325
˚
length of 2.768 A and coordination number (CN) of 8.97 aer
3 h reaction, which conrms the presence of metallic Pt on the
catalyst (spent catalyst, Table 1).
4%Pt–CeO2
95.2
154
Activities of the catalysts
3
4
No catalyst
—
—
—
—
Various CeO2 (including commercial ceria) and ceria supported
noble metal catalysts were tested for the hydrogenation of
phenol and phenolic derivatives present in bio-oil, and the
results are summarized in Table 2. The hydrogenation of
phenol produced cyclohexanol as the main product, and
cyclohexanone was formed as a major by-product in some cases.
The supported CeO2 shows no activity (Table 2, entry 1),
whereas the highest selectivity (98.6%) with 100% phenol
conversion was obtained with 2%Pt–CeO2 catalyst (Table 2,
entry 6). Pd–CeO2 (entry 4) and Ni–CeO2 (entry 2) shows activity
for phenol hydrogenation; however, the cyclohexanol selectivity
was lower than that of Pt–CeO2 catalyst. The catalytic activity of
the different metal supported CeO2 catalyst follows the order of
Pt > Pd > Ni > Re. For the 2%Pd–CeO2 catalyst, cyclohexanone
was the major product, similar to earlier studies.18 When Pt
supported on commercially available CeO2 nanopowder (Sigma-
Aldrich Co.) was used for the phenol hydrogenation reaction, it
was observed that the catalyst (Table 2, entry 8) shows not only
poor conversion (ꢀ12%), but also poor cyclohexanol selectivity.
The 2%Pt–CeOi2mp catalyst shows only 7% (Table 2, entry 10)
phenol conversion, which is possibly due to the bigger Pt
particle supported on CeO2 because of its rapid agglomeration
during the impregnation process. Therefore, nanocrystalline
CeO2 with size between 15 and 30 nm directly inuences the
activity of the Pt nanoparticles for the hydrogenation reaction.
We also believe that the synergistic effect between the Pt
nanoparticle and nanocrystalline CeO2 plays a crucial role for
such high activity during the hydrogenation reaction. The
activity of our Pt–CeO2 catalyst is very high compared to most of
the Pd supported catalysts (Table 2, entry 11–15) reported in the
literature.19 The TOF (turn over frequency) of the previously
reported Pd–C catalyst2b is ꢀ92 hÀ1, and a three-fold increase in
TOF (325 hÀ1) was observed for our Pt–CeO2 catalyst.
2%Pt–CeO2
98.9
321
5
6
2%Pt–CeO2
2%Pt–CeO2
98.5
95.3
320
309
7
2%Pt–CeO2
2%Pt–CeO2
96.1
92.7
312
301
8
a
Reaction conditions: 10 mmol of reactant, 20 ml H2O, 0.1 g reduced
catalyst; conversion and product selectivity in mol%; cc: conversion of
phenol; cs: product selectivity and cF: turnover frequency (TOF) in hÀ1
.
negligible activity. Therefore, we assume nanocrystalline CeO2
support has a denite role for the hydrogenation reaction. It has
to be noted that Pt supported on CeO2 forms a nanoparticle
with a size of 1–3 nm. We believe that 1–3 nm Pt nanoparticles
are the active species for the hydrogenation reaction, and the
size of the CeO2 particle also favours the hydrogenation reac-
tion. The synergy between 1 and 3 nm Pt nanoparticles and 15–
30 nm CeO2 nanoparticles plays a crucial role for very high
hydrogenation activity.
No reaction took place when the reaction was carried out
without a catalyst under similar conditions (Table 3, entry 3).
We have also tested the activity of the 2%Pt–CeO2 catalyst to
other phenolic derivatives present in bio-oil, and the results are
Effect of different reaction parameters
shown in Table 3. The Pt–CeO2 catalyst shows very high In order to optimize the loading of Pt, we have tested the
conversion and selectivity for all the cases. Hydroxy phenol hydrogenation of phenol with various amounts of Pt loaded
shows almost 99% conversion with 99% 3-hydroxycyclohex- catalyst, and the results are shown in Fig. S7, ESI.† When the Pt
anone selectivity (Table 3, entry 4), whereas methyl substituted loading was reduced to 1%, the phenol conversion drops to
phenols also encountered >95% conversion. Only Pt oxide does 50%, keeping the selectivity almost the same. However, with an
not show any activity, whereas commercial CeO2 showed increase in the Pt loading (4%), the catalyst showed almost
18402 | J. Mater. Chem. A, 2014, 2, 18398–18404
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry A
nanoparticles on nanocrystalline CeO2 is likely caused by their
extremely small size and the synergy between the well-dispersed
Pt nanocrystalline CeO2 (15–30 nm). Furthermore, the catalyst
did not show any evidence of leaching even aer ve reuses,
conrming the true heterogeneity of the catalyst.
Acknowledgements
B.S. acknowledges University Grant Commission (UGC), India,
for the fellowship. R.B. thanks CSIR, New Delhi, for the nan-
cial support in the form of Network Project (CSC-0125 and CSC-
0117) under 12 FYP. We thank Mr Rajib Singha for his assis-
tance in catalyst preparation. We also acknowledge Director,
CSIR-IIP, for his support. The authors thank Analytical Science
Division, Indian Institute of Petroleum for analytical services.
Prof. Suresh Bhargava, Dr Selvakannan and Dr Deepa Dumbre
are specially acknowledged for their help in XPS measurement.
The XAFS measurements were performed at KEK-IMSS-PF with
the approval of the Photon Factory Advisory Committee (project
2010G109).
Fig. 5 Influence of H2 pressure as a function of phenol conversion and
cyclohexanol selectivity.
similar phenol conversion, but the cyclohexanol selectivity
decreased (Table 3, entry 2). This is most probably due to the
formation of the bigger Pt particle (>5 nm) on CeO2 support
(Table 3, entry 2). It was also found that temperature has a
considerable effect on phenol conversion as shown in Fig. S8,
ESI.† The conversion of phenol increased with increase in
temperature from ambient temperature (ꢀ25 ꢁC) to 100 ꢁC.
Furthermore, the effect of H2 pressure also shows a linear
relationship with the phenol conversion as well as the cyclo-
hexanol selectivity. We noticed that the lower H2 pressure fav-
oured cyclohexanone formation, and on increasing H2 pressure
from 0.5 to 3 MPa, the formation of cyclohexanol dominated
(Fig. 5).
Notes and references
1 E. Furimsky, Appl. Catal., A, 2000, 199, 147.
2 (a) S. Czernik and A. V. Bridgwater, Energy Fuels, 2004, 18,
590; (b) C. Zhao, J. He, A. A. Lemonidou, X. Li and
J. A. Lercher, Angew. Chem., Int. Ed., 2009, 48, 3987; (c)
C. Zhao, J. He, A. A. Lemonidou, X. Li and J. A. Lercher, J.
Catal., 2011, 280, 8.
3 Z. Li, M. Garedew, C. H. Lam, J. E. Jackson, D. J. Miller and
C. M. Saffron, Green Chem., 2012, 14, 2540.
4 (a) F. Schwab, M. Lucas and P. Claus, Angew. Chem., Int. Ed.,
2011, 50, 10453; (b) T. P. Vispute and G. W. Huber, Green
Chem., 2009, 11, 1433; (c) F. H. Mahfud, F. Ghijsen and
H. J. Heeres, J. Mol. Catal. A: Chem., 2007, 264, 227.
5 Y. Li, X. Xu, P. Zhang, Y. Gong, H. Li and Y. Wang, RSC Adv.,
2013, 3, 10973.
Reusability of the catalyst
The reusability of the catalyst Pt–CeO2 was studied without any
regeneration. The catalyst was repeatedly washed with water
and acetone and dried overnight at 100 ꢁC and used as such. It
was observed that the catalyst does not change its activity
(conversion and selectivity) aer ve successive runs (Table 2,
entry 9). The amount of Pt present in the catalyst aer four runs
is almost same as in the fresh catalyst (estimated by ICP-AES),
conrming the true heterogeneity of the catalyst.
6 J. Chen, W. Zhang, L. Chen, L. Ma, H. Gao and T. Wang,
ChemPlusChem, 2013, 78, 142.
7 (a) H. Liu, T. Jiang, B. Han, S. Liang and Y. Zhou, Science,
2009, 326, 1250; (b) H. Li, J. Liu, S. H. Xie, M. H. Qiao,
W. L. Dai, Y. F. Lu and H. X. Li, Adv. Funct. Mater., 2008,
18, 3235.
8 (a) K. J. C. van Bommel, A. Friggeri and S. Shinkai, Angew.
Chem., Int. Ed., 2003, 42, 980; (b) S. Mann, S. L. Burkett,
S. A. Davis, C. E. Fowler, N. H. Mendelson, S. D. Sims,
D. Walsh and N. T. Whilton, Chem. Mater., 1997, 9, 2300.
9 (a) Y. Li, Y. Wu and B. S. Ong, J. Am. Chem. Soc., 2005, 127,
3266; (b) H. Hiramatsu and F. E. Osterloh, Chem. Mater.,
2004, 16, 2509.
Conclusions
We have demonstrated a simple method for the preparation of
ꢀ1–3 nm Pt nanoparticles supported on nanocrystalline CeO2
with a diameter of around 15–30 nm for the direct conversion of 10 (a) B. Sarkar, C. Pendem, L. N. Konathala, R. Tiwari, T. Sasaki
phenol and phenolic component of bio-oil. The catalyst shows a
conversion of ꢀ98–100% of phenol and its derivatives in the
presence of molecular H2. The catalyst was characterized by
XRD, XPS, ICP-AES, EXAFS, SEM and TEM. The activity of the
catalyst was found to depend on Pt loading and the size of the Pt
particles. The enhanced activity and stability of ꢀ1–3 nm Pt
and R. Bal, Chem. Commun., 2014, 50, 9707; (b) S. Ghosh,
S. S. Acharyya, R. Tiwari, B. Sarkar, R. K. Singha,
C. Pendem, T. Sasaki and R. Bal, ACS Catal., 2014, 4, 2169;
(c) B. Sarkar, R. K. Singha, R. Tiwari, S. Ghosh,
S. S. Acharyya, C. Pendem, L. N. S. Konathala and R. Bal,
RSC Adv., 2014, 4, 5453; (d) S. S. Acharyya, S. Ghosh and
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 18398–18404 | 18403

View Article Online
Journal of Materials Chemistry A
Paper
R. Bal, ACS Sustainable Chem. Eng., 2014, 2, 584; (e) 15 V. Z. Fridman and A. A. Davydov, J. Catal., 2000, 195, 20.
S. S. Acharyya, S. Ghosh and R. Bal, Chem. Commun., 2014, 16 (a) T. Taniguchi, K. Katsumata, S. Omata, K. Okada and
DOI: 10.1039/c4cc02937b; (f) S. S. Acharyya, S. Ghosh,
R. Tiwari, B. Sarkar, R. K. Singha, T. Sasaki, C. Pendem
and R. Bal, Green Chem., 2014, 16, 2500; (g) S. Ghosh,
S. S. Acharyya, S. Adak, L. N. Sivakumar and R. Bal, Green
Chem., 2014, 16, 2826.
N. Matsushita, Cryst. Growth Des., 2011, 11, 3754; (b)
J. F. Moulder, W. F. Stickle, P. E. Sobol and K. D. Bomben,
in A Reference Book of Standard Spectra for Identication and
Interpretation of XPS Data, Physical Electronics Division,
Perkin-Elmer Corp., Eden Prairie, USA, 1992; (c)
C. D. Wagner, W. M. Riggs, L. E. Davis, J. F. Moulder and
G. E. Muilenberg, in Handbook of X-ray Photoelectron
Spectroscopy, Perkin-Elmer Corp., Eden Prairie, USA, 1979.
11 A. K. Suresh, M. M. Sharma and T. Sridhar, Ind. Eng. Chem.
Res., 2000, 39, 3958.
12 B. Sarkar, P. Prajapati, R. Tiwari, R. Tiwari, S. Ghosh,
S.
S.
Acharyya,
C.
Pendem,
R.
K.
Singha, 17 C. Pendem, P. Gupta, N. Chaudhary, S. Singh, J. Kumar,
L. N. S. Konathala, J. Kumar, T. Sasaki and R. Bal, Green
Chem., 2012, 14, 2600.
13 C. A. Gibson, U.S. Pat. 3998884, 1976.
T. Sasaki, A. Datta and R. Bal, Green Chem., 2012, 14, 3107.
18 Y. Wang, J. Yao, H. Li, D. Su and M. Antonietti, J. Am. Chem.
Soc., 2011, 133, 2362.
14 (a) A. Bellifa, D. Lahcene, Y. Tchenar, A. Choukchoham, 19 (a) J. F. Zhu, G. H. Tao, H. Y. Liu, L. He, Q. H. Sun and
R. Bachir, S. Bedrane and C. Kappensteine, Appl. Catal., A,
2006, 305, 1; (b) F. P. Canhota, G. C. Salomao,
N. M. F. Carvalho and O. A. C. Antunes, Catal. Commun.,
2008, 9, 182; (c) G. B. Shulpin, M. M. Bochkova and
G. V. Nizova, J. Chem. Soc., Perkin Trans. 1, 1995, 2, 1465.
H. C. Liu, Green Chem., 2014, 16, 2664; (b) P. Makowski,
R. D. Cakan, M. Antonietti, F. Goettmann and
M. M. Titirici, Chem. Commun., 2008, 8, 999.
18404 | J. Mater. Chem. A, 2014, 2, 18398–18404
This journal is © The Royal Society of Chemistry 2014