Porphyrin-based porous organic polymer-supported iron(III) catalyst for efficient aerobic oxidation of 5-hydroxymethyl-furfural into 2,5-furandicarboxylic acid

Article abstract of DOI:10.1016/j.jcat.2012.12.024

Environmentally friendly and efficient synthesis of 2,5-furandicarboxylic acid (FDCA), a polyester building block chemical from biomass, was carried out in water by aerobic oxidation of 5-hydroxymethylfurfural (HMF) with highly cross-linked, robust structured, and thermally stable Fe^III-porous organic polymer (Fe^III-POP-1) material containing basic porphyrin subunits and iron metal center. EPR analysis confirmed that the catalyst retained the oxidation state of Fe(III) after catalysis and can be reused.

Full text of DOI:10.1016/j.jcat.2012.12.024

Journal of Catalysis 299 (2013) 316–320
Contents lists available at SciVerse ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Priority Communication
Porphyrin-based porous organic polymer-supported iron(III) catalyst
for efficient aerobic oxidation of 5-hydroxymethyl-furfural into
2,5-furandicarboxylic acid
Basudeb Saha a, , Dinesh Gupta a, Mahdi M. Abu-Omar b, , Arindam Modak c, Asim Bhaumik c
⇑
⇑
a Laboratory of Catalysis, Department of Chemistry, University of Delhi, Delhi 110 007, India
b Brown Laboratory, Department of Chemistry, The Center for Catalytic Conversion of Biomass to Biofuels (C3Bio), 560 Oval Drive, Purdue University, IN 47907, USA
c Department of Material Science, Indian Association for the Cultivation of Science, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Environmentally friendly and efficient synthesis of 2,5-furandicarboxylic acid (FDCA), a polyester build-
ing block chemical from biomass, was carried out in water by aerobic oxidation of 5-hydroxymethylfurf-
ural (HMF) with highly cross-linked, robust structured, and thermally stable FeIII–porous organic polymer
(FeIII–POP-1) material containing basic porphyrin subunits and iron metal center. EPR analysis confirmed
that the catalyst retained the oxidation state of Fe(III) after catalysis and can be reused.
Ó 2013 Elsevier Inc. All rights reserved.
Received 10 October 2012
Revised 7 December 2012
Accepted 20 December 2012
Available online 1 February 2013
Keywords:
5-Hydroxynethylfurfural (HMF)
2,5-Furandicarboxylic acid (FDCA)
Porous organic polymer
FeIII catalyst
Aerobic oxidation
1. Introduction
polyamides, polyesters, and polyurethanes [10]. A furan counter-
part of PET called poly(ethylene 2,5-furandicarboxylate) (PEF) has
Nonrenewable fossil sources, such as coal, natural gas and
petroleum, are the sole and essential resource for energy and
chemicals [1]. Rapid depletion of nonconventional fossil resources,
the awareness of climate change and the high volatility in crude oil
price, caused by imbalance in demand–supply, have put tremen-
dous pressure on the global economy [2,3]. Terephthalic acid
(PTA) is one such commodity chemical, which is produced in large
scale from petroleum-based para-xylene [4,5] for the manufacture
of polyethylene terephthalate (PET), a polymer commonly made
into consumer goods for thousands of applications [6,7]. Besides
usage of petroleum feedstock, the oxidation of para-xylene in cor-
rosive acetic acid solvent results in release of greenhouse gases,
carbon dioxide, and carbon monoxide [8]. Therefore, chemical
industries are shifting their focus to the development of sustain-
able manufacturing processes for aromatic carboxylic acids, prefer-
ably utilizing abundant cellulosic and hemicellulosic biomass in
environmentally benign solvent [9]. In this context, 2,5-furandi-
carboxylic acid (FDCA) has received significant attention as a desir-
able substitute for terephthalic acid for the manufacture of
been recently prepared from renewable sources, and it showed
comparable thermal stability to PET [11].
The preferred route of FDCA production involves efficient cata-
lytic transformation of biomass or biomass-derived carbohydrates
to 5-hydroxymethylfurfural (HMF) [12–14] followed by catalytic
oxidation of HMF (Scheme 1) [15,16]. The aerobic oxidation of
HMF to FDCA was examined with the homogeneous metal acetate
catalyst comprising cobalt acetate (Co(OAc)2), manganese acetate
(Mn(OAc)2) and a bromide promoter, HBr, commonly known as
the Amoco Mid-Century (MC) catalyst, at 70 bar air pressure in ace-
tic acid solvent [17]. Although both hydroxymethyl (ACH2OH) and
aldehyde groups of HMF could simultaneously oxidize, the authors
described the possibility of hydroxymethyl group being preferen-
tially oxidized first. Similar observation was noted in a recent pub-
lication using Co(OAc)2/Zn(OAc)2/NaBr catalyzed oxidation of HMF
[15], where 2,5-diformylfuran (DFF) was the sole oxidation product
without an acid additive. In the presence of trifluoroacetic acid
(HTFA) as an additive, the Co(OAc)2/Zn(OAc)2/NaBr catalyzed reac-
tion progressed beyond DFF enabling a maximum 60% FDCA yield.
The aerobic oxidation of HMF to FDCA has also been reported with
heterogeneous catalysts. Vinke et al. used alumina-supported plat-
inum for the liquid-phase oxidation of HMF, giving 5-formyl-2-
furancarboxylic acid (FFCA) as the main oxidation product [18].
In a subsequent communication, the authors demonstrated near
⇑
Corresponding authors. Fax: +91 11 2766 9974 (B. Saha), fax: +1 765 494 0239
(M.M. Abu-Omar).
E-mail addresses: bsaha@chemistry.du.ac.in (B. Saha), mabuomar@purdue.edu
(M.M. Abu-Omar).
0021-9517/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jcat.2012.12.024

B. Saha et al. / Journal of Catalysis 299 (2013) 316–320
Lignocellulosic biomass
317
O
HOOC
COOH
COOH
O
Hydrolysis
Glucose
Isomerization
OHC
CHO
FDCA
DFF
0.5 O2
OHC
0.5 O2
O
CHO
HO
0.5 O2
O
Fructose
Dehydration
HMF
0.5 O2
FFCA
0.5 O2
HOOC
CH2OH
O
HMFCA
Scheme 1. Possible oxidation sequence of HMF to FDCA.
quantitative FDCA yield with the same catalyst, Pt/Al2O3, in the
presence of a homogeneous base additive [19]. Lilga et al. patented
an oxidation method of HMF using Pt/ZrO2 catalyst and claimed
the formation of DFF and FFCA with 68% and 32% selectivity,
respectively [20]. Although one-pot conversion of fructose to FDCA
has been attempted using PtBi/C and Co(acac)/SiO2 catalyst, the
process suffered either from poor FDCA yield or harsh reaction con-
ditions [21,22].
Nanoparticulate catalyst, Au/TiO2, has been reported to be supe-
rior in HMF oxidation, enabling 98% 2,5-furandimethylcarboxylate
(FDMC) in methanol at 130 °C and 4 bar oxygen pressure [23].
However, the reaction needed a base additive, sodium methoxide.
The presence of a base additive, NaOH, was also critical in Au/TiO2
and Au/CeO2 catalyzed oxidation of HMF, without which the reac-
tion suffered by poor FDCA selectivity [24,25]. Without base, the
authors claimed catalyst deactivation by the initially formed oxida-
tion intermediates. In contrast, we reported that an acid additive,
HTFA, improved both HMF conversion and FFCA selectivity in Au/
TiO2 and Au/CeO2 catalyzed oxidation in acetic acid solvent [15].
Most recently, Ebitani et al. demonstrated high yield of FDCA from
HMF using hydrotalcite-supported gold nanoparticulate catalyst in
water at 95 °C without addition of a base [16].
Although homogeneous and metal oxide/hydrotalcite-
supported heterogeneous catalysts have been used for HMF
oxidation, the application of heterogeneous porphyrin-based por-
ous organic polymer (POP)-loaded with metal catalysts for similar
oxidation is not known. A series of highly cross-linked, robust
structured, and thermally stable Fe–POP materials containing basic
porphyrin subunits have been recently synthesized in the presence
of FeIII via a simple one-pot bottom-up approach [26]. Among dif-
ferent Fe–POPs synthesized using this strategy, the hierarchically
porous material cross-linked with terephthaldialdehyde possess
the maximum surface area (875 m2 gÀ1) and hence this material
(henceforth referred as FeIII–POP-1) was chosen as a catalyst for
investigating HMF oxidation with molecular oxygen as oxidant in
aqueous medium.
2.2. Synthesis of Fe(III)–POP-1 catalyst
FeIII–POP-1 material was synthesized according to the literature
procedure by reacting freshly distilled pyrrole (0.05 g, 0.74 mmol)
with terephthaldehyde (0.1 g, 0.74 mmol) in the presence of 1.2
equivalent of FeCl3 in 15 mL acetic acid in a Teflon-lined autoclave
under hydrothermal treatment for 72 h at 180 °C [26]. After reac-
tion for 72 h, the oven temperature was slowly cooled to room
temperature. The resulting dark brownish precipitate was filtered
and washed by Soxhlet extraction for 24 h with water, dichloro-
methane, methanol and THF, respectively. The washed material
was then dried in an oven at 80 °C for another 48 h. The yield of
Fe–POP-1 was 0.2 g (44% based on terephthaldehyde and pyrrole).
2.3. Characterization
Carbon, hydrogen, and nitrogen contents were determined
using a Perkin Elmer 2400 Series II CHN analyzer. Fourier Trans-
form Infra Red (FTIR) spectrum of Fe–POP-1 was recorded using
a Nicolet MAGNA-FT IR 750 Spectrometer Series II. 1H and 13C
NMR experiments (liquid state) were carried out on a Bruker
DPX-300 NMR spectrometer. Nitrogen-sorption experiments and
micropore analysis were conducted at 77 K using a Beckman Coul-
ter, SA 3100 surface area measurement instrument. Prior to
adsorption measurement, the samples were degassed in vacuum
at 180 °C for about 3 h. NLDFT pore-size distributions were deter-
mined using the carbon/slit-cylindrical pore model of the Auto-
sorb-1 software. The 13C cross-polarization magic angle spinning
(CP-MAS) NMR spectrum was obtained on a Bruker Advance
III600WB 600 MHz at 150.9 MHz and a MAS frequency of 12 kHz.
A Hitachi S-5200 field-emission scanning electron microscope
was used for the determination of the morphology of the particles.
Low-temperature EPR measurement of the catalyst was performed
on a Bruker EMX-EPR spectrometer.
2.4. HMF oxidation
Progression of HMF oxidation under atmospheric oxygen pres-
sure was carried out in a glass reactor equipped with a manometer
and impeller with magnetic bar for oxygen saturation in the solu-
tion. HMF oxidations under high pressures and temperatures were
carried out in a Parr reactor (model 5000 multi reactor heating/
stirrer system). After the reaction for the desired time, 0.1 mL ali-
quot was collected from the reaction mixture and diluted to 1 mL
in methanol. Before collecting the aliquot, the reaction mixture
was stirred rapidly so that the sole particles are homogeneously
mixed throughout the solution. Methanol diluted solution was
2. Methods
2.1. Chemicals
Pyrrole was purchased from SRL, India, and distilled under ar-
gon gas prior to use. Terephthaldehyde was received from Sigma-
Aldrich, USA. Glacial acetic acid, methanol, acetone, tetrahydrofu-
ran, and dichloromethane were purchased from Merck, India, and
Sigma-Aldrich. HMF of ꢀ99% purity was purchased from Sigma-
Aldrich. Authentic samples of FDCA, DFF, FFCA were obtained from
TCI, India, and analyzed as received.
then filtered through a 0.22 lm cut-off syringe filter (25 mm diam-
eter) for analysis by using a GC (Agilent Technology, model 6890N)
equipped with a FID detector and DB-5 column of dimension

318
B. Saha et al. / Journal of Catalysis 299 (2013) 316–320
30
l
m  250
l
m  0.25
l
m. The oxidation products were identi-
be due to its loss during recovery. The heterogeneity of the catalyst
was further confirmed by the hot-filtration experiment. In this
experiment, a reaction was started under the conditions of Exper-
iment 1 in Table 1 and the volume of oxygen uptake as a function
of time was recorded for 70 min. After 70 min, the catalyst was
separated from the reaction mixture by filtration through sintered
glass crucible and the filtrate transferred into the reactor. The reac-
tion was resumed without the solid catalyst. Oxygen consumption
was not observed, confirming the catalyst is indeed heterogeneous.
A comparison of oxygen uptake as a function of reaction time for
experiment containing the catalyst and that for the hot filtration
experiment is deposited in the supporting information. (Fig. S11).
To test the influence of room light on the observed catalytic effec-
tiveness for the reactions carried out in glass reactor, a reaction un-
der the conditions of Experiment 1 in Table 1 was repeated in the
dark. Similar initial rates for the reactions carried out in dark
(vi = 27 Â 10À5 mol LÀ1 minÀ1) and that in the presence of room
light (vi = 29 Â 10À5 mol LÀ1 minÀ1) preclude the possibility of sig-
nificant photocatalysis.
The effectiveness of the catalyst was further evaluated by con-
ducting the HMF oxidation reactions for a longer time under atmo-
spheric O2 pressure and analyzing the products by GC. A reaction
under the conditions of 0.2 mmol HMF, 4 mg catalyst (0.05 mmol
HMF/1 mg catalyst), 6 mL water and at 70 °C for 9 h produced
69% 2,5-diformylfuran (DFF) as the only product. The identity of
DFF in the reaction product was also confirmed by 1H NMR
(Fig. S8). When the amount of catalyst was doubled to 8 mg
(0.025 mmol HMF/1 mg catalyst) in the above reaction, FDCA was
detected as a reaction product with the formation of 66% DFF
and 22% FDCA in 9 h under similar reaction conditions. The forma-
tion of DFF as an oxidation product attributes to the fact that the
hydroxymethyl group of HMF oxidizes first followed by the oxida-
tion of aldehyde group. This observation of hydroxymethyl group
being oxidized first agrees with our previous report [15] and with
Partenheimer and Grushin’s findings [17]. The partially oxidized
intermediate, DFF, was also obtained from HMF, both as a starting
substrate and after producing it in a one-pot conversion from fruc-
tose [27,28]. The exact pathway of HMF oxidation to FDCA is a mat-
ter of debate. In contrast to the above observation, HMF oxidation
with basic hydrotalcite-supported gold catalyst in aqueous med-
ium [16], and Au/TiO2 and Au/CeO2 catalysts in methanol in the
presence of homogeneous base additive [24,25], has been reported
to occur via the oxidation of the aldehyde group in the first step
followed by the hydroxymethyl group.
fied by their retention times in comparison with authentic sam-
ples. Each peak of the GC chromatogram was properly integrated,
and the actual concentration of each component was obtained
from the pre-calibrated plot of peak area
3. Results and discussions
AAS analysis of this material reveals the presence of
0.00267 mmol of Fe/g of FeIII–POP-1. The FT-IR spectrum of FeIII–
POP (Fig. S1) suggests the absence of C@O group of terephthaldial-
dehyde linker (1720–1740 cmÀ1) and thus confirming the forma-
tion of polymeric network. A new vibration band at 1001 cmÀ1
confirmed a strong coordination of Fe with porphyrin units. X-band
EPR of FeIII–POP-1 was collected at 25 K and has g-values of 8.5, 4.2
and 2.0, which can be attributed to a high spin Fe(III) species
(Fig. S2). The solid-state 13C spectrum of FeIII–POP-1 (Fig. S3) also
confirmed complete polymerization between the pyrrole and alde-
hyde linker. FE-SEM image showed uniform nanospheres of dimen-
sion ca. 50–100 nm, which are self-assembled to form uniform
large spherical particles of ca. 300–500 nm (Fig. S4). HRTEM anal-
ysis further revealed that the nanospheres have micropores having
dimension ca. 1.0 nm (Fig. S5). N2-sorption isotherm for FeIII–POP-
1 showed type I isotherm, typical for microporous solid (Fig. S6)
with a BET surface area of 875 m2 gÀ1 and pore volume of 0.4 ccgÀ1
.
Peak pore diameter was ca. 1.1 nm (inset of Fig. S6), which agrees
very well with the HRTEM results. The characterization data of
FeIII–POP-1 (FR-IR, EPR, 13C NMR, FE-SEM, HRTEM and N2-sorption
isotherm) are deposited in the supporting information.
In preliminary experiments, HMF oxidation with molecular
oxygen in the presence of the FeIII–POP-1 catalyst was carried
out under mild reaction conditions using water as a solvent. The
progression of reaction was monitored by the oxygen uptake
method [5]. The initial change in the volume of O2 against time
was linear for a reaction between 0.2 mmol HMF and 4 mg catalyst
in 6 mL water at 70 °C and 1 bar O2 pressure. The slope of the linear
plot, when converted to concentration unit, gave the initial reac-
tion rate as vi = 30 Â 10À5 mol LÀ1 minÀ1 (Expt. 1 in Table 1). To
confirm this catalytic effectiveness, a blank experiment was carried
out without the catalyst, which showed no oxygen consumption
under identical reaction conditions. More experiments at varying
HMF concentrations and temperatures showed a variation in the
initial rates; vi values increased from 14 Â 10À5 to 51 Â 10À5
-
mol LÀ1 minÀ1 upon increasing the temperatures from 40 to
85 °C. A small increase in vi value from 29 Â 10À5 to 38 Â 10À5
-
mol LÀ1 minÀ1 was noted for increasing the HMF concentration
from 0.2 mmol to 0.8 mmol. Because of the heterogeneity of the
catalyst, it was easily separated from the reaction mixture and re-
used for HMF oxidation without adding any fresh catalyst to
replenish its loss during recovery. Under the reaction conditions
of Expt. 1 in Table 1, the initial rates of HMF oxidation using the
recovered catalyst varied from 30 Â 10À5 (1st cycle) to 28 Â 10À5
(2nd cycle) to 25 Â 10À5 (3rd cycle), suggesting that the catalyst
can be reused for three catalytic cycles without significant loss in
its activity. A slight loss in initial rates by the reused catalyst could
120
100
FDCA
HMF
80
60
40
Table 1
FFCA
DFF
Initial reaction rates for aerobic oxidation of with FeIII–POP-1 catalyst.
20
0
Expt. #
HMF (mmol)
T (°C)
Vi  10À5 (mol LÀ1 minÀ1
29
38
14
51
)
1
2
3
4
0.2
0.8
0.4
0.4
70
70
40
85
0
2
4
6
8
10
12
Time, h
Fig. 1. The reaction profile for HMF oxidation with FeIII–POP-1 catalyst at 100 °C.
Other reaction conditions: Catalyst = 4 mg, water = 6 mL, P = 1 bar of pure O2.

B. Saha et al. / Journal of Catalysis 299 (2013) 316–320
319
Table 2
HMF oxidation with FeIII–POP-1 catalyst in water using pure oxygen or air as a source oxidant.
Expt. #
HMF (mmol)
Cat. (mg)
Oxidant, pressure
Time (h)
Conv. (%)
Product (%)
DFF
FFCA
FDCA
1
2
3
4
5
6
1.58
1.58
0.4
1.58
1.58
1.58
6
3
2
5.5
5
O2, 10 bar
O2, 5 bar
O2, 5 bar
Air, 4 bar
Air, 10 bar
Air, 10 bar
3
3
5
5
5
72
63
100
42
80
100
19
31
9
15
12
7
7
9
5
12
9
8
40
20
75
14
53
79
6
10
Other reaction conditions: temperature = 100 °C, H2O = 10 mL.
To examine the effectiveness of the FeIII–POP-1 catalyst at high-
er pressure and temperature, more experiments were performed at
100 °C under 4–10 bar pressure of pure oxygen or air as a source of
oxidant. One such reaction under 10 bar oxygen pressure using
1.58 mmol HMF, 6 mg catalyst (0.26 mmol HMF/1 mg catalyst),
and 10 mL water was carried out for multiple times by varying
the reaction time from 1 h to 10 h. The reaction profile, as shown
in Fig. 1, reveals complete oxidation of HMF in 10 h with 85% selec-
tivity for FDCA. It is reasonable to envisage that small amount of
unconverted FFCA (7%) and DFF (4%) remained in the solution will
further oxidize upon continuing the reaction for longer time. The
effectiveness of the catalyst was further evaluated by performing
HMF oxidation at varying reaction parameters, such as pure O2 ver-
sus air as O2 source, concentration of HMF per mg of catalyst, and
pressure of oxidant. The percentage of HMF conversion and the
corresponding yields of the oxidation products are shown in Ta-
ble 2. Complete oxidation of HMF with maximum FDCA yield
was realized for experiments 3 and 6 (Table 2) where concentra-
tions of HMF/mg of catalyst were in the range of 0.2–0.26 mmol
and the reactions were conducted under 5 bar pure O2 for 5 h
and 10 bar air for 10 h.
oxygen and nitrogen atmosphere resulted in the formation of pale
bluish and intense blue-colored solution, respectively (deposited in
the supporting information). These observations suggest that TBP
radical was indeed formed in our HMF oxidation reaction; how-
ever, the characteristic blue color of TBP radical was not observed
due to its rapid reaction with oxygen. A plausible catalytic oxida-
tion of RH (where R = CHO(C4H2O)CHOH) would involve a classical
Fenton-type reaction of the iron with the peroxides ROOH formed
via thermal autoxidation. However, the role of the catalyst FeIII–
POP-1 in initiating RÅ radical formation cannot be excluded because
in the absence of catalyst under our reaction conditions autoxida-
tion to peroxide (ROOH) was not observed.
4. Conclusions
In conclusion, the catalytic effectiveness of highly cross-linked,
robust structured, and thermally stable FeIII–POP-1 materials con-
taining basic porphyrin subunits and FeIII metal was investigated
for HMF oxidation with molecular oxygen in aqueous medium.
The investigated catalyst was highly effective for the oxidation of
HMF to FDCA. The oxidation state of Fe in the catalyst remained in-
tact after catalysis and hence the catalyst can be reused without
any significant loss in activity. Catalytic ineffectiveness of homoge-
neous FeIII–porphyrin complex for HMF oxidation under similar
conditions suggested that the metal active site of the FeIII–POP-1
catalyst played an important role. A plausible radical chain mech-
anism for HMF oxidation would involve thermal autoxidation of
the organic substrate to peroxides, which would lead to products
via Fenton-type homolytic cleavage of the ROAOH bond over iron.
To test the oxidation state of Fe in FeIII–POP-1 after catalysis, the
catalyst was recovered from the reaction mixture, washed, and air-
dried. The recovered catalyst was suspended in water and EPR was
collected at 25 K, which showed signals corresponding to g-values
of 8.5, 4.2 and 2.0 (Fig. S8), suggesting that +3 oxidation state of Fe
in FeIII–POP-1 remained intact after catalysis. Additional experi-
ments using homogeneous FeIII–porphyrin complex [FeIII(TF4-
TMP)]5+ [29] as a catalyst for HMF oxidation showed no product
formation, suggesting that high surface area and metal active sites
of the FeIII–POP-1 catalyst played an important role for the oxida-
tion to takes place. Ebitani and co-workers [16] have also shown
that the metal active sites on hydrotalcite-supported Au catalyst
were responsible for its effective HMF catalysis. Similar to para-xy-
lene oxidation to terephthalic acid, the oxidation of HMF with the
MC catalyst is reported to occur via the formation of peroxyl radical
in the chain propagation step [17]. The peroxyl radicals are formed
through the abstraction of H-atom of HMF by the bromide radical,
generated in the catalytic cycle by the oxidation of HBr with Co(III)
or Mn(III), followed by reaction of arylalkyl radical with O2. The
present oxidation of HMF with the FeIII–POP-1 catalyst is also be-
lieved to proceed via a radical chain mechanism with the forma-
tion of peroxyl radical in the catalytic cycle. This hypothesis of
radical formation was tested by carrying out a reaction between
HMF and molecular oxygen in the presence of FeIII–POP-1 catalyst
and 2,4,6-tri-t-butyl phenol (TBP). TBP was chosen because of the
characteristic intense blue color of the corresponding phenoxy rad-
ical [30]. However, instead of the expected blue color for the TBP
radical, pale bluish color developed in the reaction mixture, which
could be due to rapid reaction of TBP radical with molecular oxy-
gen as discussed by Cook and Woodworth [30]. Separate reactions
for the formation of TBP radical with potassium ferricyanide under
Acknowledgments
Authors acknowledge Dooshaye Moonshiram and Dr. Trenton
Parsell for their help in collecting EPR spectra and interpreting
EPR results. BS acknowledges the financial support by the Univer-
sity Grants Commission (UGC), India, and the University of Delhi.
DG thanks UGC, India, for the Research Fellowship. AB thanks
DST, India, for financial supports. AM thanks CSIR, India, for a se-
nior research fellowship. M.M.A.-O. acknowledges support from
the Center for direct Catalytic Conversion of Biomass to Biofuels
(C3Bio), an Energy Frontier Research Center funded by the U.S.
Department of Energy, Office of Science, and Office of Basic Energy
Sciences under Award Number DE-SC0000997, which supported
visit exchanges to Purdue University for BS.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jcat.2012.12.024.

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B. Saha et al. / Journal of Catalysis 299 (2013) 316–320
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