Solvent-free selective oxidation of benzyl alcohol to benzaldehyde by tert-butyl hydroperoxide over U3O8-supported nano-gold catalysts

Article abstract of DOI:10.1016/j.apcata.2010.01.007

Liquid-phase oxidation of benzyl alcohol to benzaldehyde by tertiary butyl hydroperoxide over different uranium oxide supported nano-gold catalysts in the absence of a solvent has been thoroughly investigated. The influences of catalyst parameters [viz. m

Full text of DOI:10.1016/j.apcata.2010.01.007

Applied Catalysis A: General 375 (2010) 252–257
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Solvent-free selective oxidation of benzyl alcohol to benzaldehyde by tert-butyl
hydroperoxide over U O -supported nano-gold catalysts
3
8
Vasant R. Choudhary *, Deepa K. Dumbre
Chemical Engineering and Process Development Division, National Chemical Laboratory, Homibhaba Road, Pashan, Pune 411008, Maharashtra, India
A R T I C L E I N F O
A B S T R A C T
Article history:
Liquid-phase oxidation of benzyl alcohol to benzaldehyde by tertiary butyl hydroperoxide over different
uranium oxide supported nano-gold catalysts in the absence of a solvent has been thoroughly
investigated. The influences of catalyst parameters [viz. method of gold deposition (impregnation, co-
precipitation, deposition–precipitation and homogeneous deposition–precipitation), gold loading (0–
Received 3 September 2009
Received in revised form 18 December 2009
Accepted 6 January 2010
Available online 11 January 2010
8
wt%) and catalyst calcination temperature (100–900 8C)] on the catalyst performance have been
investigated. The influence of reaction conditions [viz. reaction time (0–2 h) and temperature (25–
4 8C)] on the process performance has also been studied. The Au/U catalyst prepared by the
Keywords:
9
3 8
O
Benzyl alcohol
Benzaldehyde
Partial oxidation
homogeneous deposition–precipitation and calcined at 400 8C showed very high activity (100% benzyl
alcohol conversion with >85% selectivity for benzaldehyde) in the process for a short reaction period
(0.5 h) at 94 8C. The catalyst also showed excellent reusability in the process.
3 8
Au/U O catalyst
tert-Butyl hydroperoxide
ß 2010 Elsevier B.V. All rights reserved.
Nano-gold
1
. Introduction
Benzaldehyde is an important intermediate for the production
After the pioneering work of Prof. Haruta [15], gold has
attracted the attention of a number of investigators for oxidation/
reduction reactions. Galvagno and co-workers [16,17] and Rossi
and co-workers [18,19] reported oxidation of alcohols to aldehydes
of perfumes, pharmaceuticals, dyestuffs and agrochemicals. It is
commercially produced as a by-product of the oxidation of toluene
to benzoic acid [1]. It can also be produced by the hydrolysis of
benzal chloride. However, the latter process provides benzalde-
hyde with trace contamination from chlorine which is not
acceptable in perfumes and pharmaceuticals. With regards to
chlorine-free benzaldehyde production, several studies have been
reported on the catalytic vapor-phase oxidation of benzyl alcohol
to benzaldehyde [2–7]. However, in the vapor-phase oxidation
process, a very significant carbon loss in the form of carbon oxides
is a major problem. A few studies have, therefore, also been
reported on the liquid-phase oxidation of benzyl alcohol to
benzaldehyde (which is considered as a model oxidation reaction)
over the palladium [8,9], Ni–Al hydrotalcite [10] and hetero-
polyacid [11] catalysts in the presence of different solvents.
2 3 2
using Au/Fe O and Au/SiO catalysts, respectively. Recently,
Choudhary et al. [20] reported a very good activity for a number
of nano-gold catalysts, prepared by supporting gold on different
metal oxides (such as alkaline earth, rare earth, group IIIa and
transition metal oxides), for the solvent-free oxidation of benzyl
alcohol to benzaldehyde by molecular O
nano-gold catalysts (prepared by homogeneous deposition meth-
od), the Au/U showed the best performance [20,21]. Later,
2
. Among the supported
3 8
O
Hutchings and co-workers [22,23] have reported the use of
supported gold and Au–Pd catalysts for the solvent-free oxidation
of primary alcohols to aldehydes by oxygen. It is preferable to use
O
2
over hydrogen peroxide or organic hydroperoxide as an
oxidizing agent for the benzyl alcohol-to-benzaldehyde oxidation.
However, the benzaldehyde yield obtained is low, even under
severe reaction conditions. Very recently, Wu et al. [24] have
reported the use of hydrotalcite intercalated by sulphonated-
salen–group (III) complexes for solvent-free oxidation of benzyl
ꢀ
1
Recently, the use of MnO
and other transition metal containing hydrotalcite-like solids
13,14], as an active/selective catalyst for the solvent-free
4
-exchanged Mg–Al hydrotalcite [12]
[
oxidation of benzyl alcohol to benzaldehyde, using TBHP and O
as an oxidizing agent have also been reported.
2
2 2
alcohol to benzaldehyde by H O . Although a number of studies
have already been reported for the solvent-free oxidation of benzyl
alcohol to benzaldehyde, either the conversion of benzyl alcohol or
the selectivity for benzaldehyde has been low. Hence, there is a
need to develop a more active and selective catalyst and/or a more
environmentally benign process for the oxidation of benzyl
alcohol.
*
Corresponding author. Tel.: +91 20 25902318; fax: +91 20 25902612.
E-mail addresses: vr.choudhary@ncl.res.in, vrc0001@yahoo.co.in
(V.R. Choudhary).
0926-860X/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.01.007

V.R. Choudhary, D.K. Dumbre / Applied Catalysis A: General 375 (2010) 252–257
253
3 8 3 8
Fig. 1. TEM photographs of (a) Au/U O (DP) and (b) Au/U O (CP) (both calcined at 400 8C).
Our earlier work [20,21] revealed that among the different
metal oxide supported gold catalysts the U -supported catalyst
showed the best performance in the benzyl alcohol-to-benzalde-
hyde oxidation (using O [20] or TBHP [25] as the oxidizing agent).
Earlier, U was used as a catalyst for the oxidative destruction of
benzaldehyde in the solvent-free oxidation of benzyl alcohol by
aqueous TBHP over Au/U catalyst [prepared by the homoge-
3
O
8
3 8
O
neous deposition–precipitation (HDP) method] at shorter reaction
periods (ꢁ0.5 h) and also under milder conditions (at <100 8C)
than those employed earlier. The influences of different catalyst
parameters (viz. method of gold deposition, Au loading and
catalyst calcination temperature) and reaction conditions (viz.
2
3 8
O
chloro organic compounds [26]. In this paper we report that benzyl
alcohol can be completely converted with high selectivity for
3 8
Fig. 2. TEM photographs of Au/U O (HDP) catalyst calcined at different temperatures [(a) 400 8C, (b) 700 8C, and (c) 900 8C].

2
54
V.R. Choudhary, D.K. Dumbre / Applied Catalysis A: General 375 (2010) 252–257
catalyst concentration and reaction period and temperature) on
the process performance have also been exhaustively investigated.
2
. Experimental
3 8
Preparation of Au/U O catalysts by different gold deposition
methods, such as the impregnation (IMP), deposition–precipita-
tion (DP), homogeneous deposition–precipitation (HDP) and co-
precipitation (CP) has been described earlier [21].
Unless otherwise mentioned, the catalysts were calcined at
4
00 8C for 2 h. The catalysts were characterized for their Au content
by ICP-OES), Au particle size [by the XRD peak (at 2 = 38.28)
broadening and also by TEM] and surface area (by the single point
(
u
N
2
adsorption method).
The liquid-phase oxidation of benzyl alcohol over the catalysts
was carried out in a magnetically stirred round bottom flask
3
(
capacity: 25 cm ), provided with a mercury thermometer (for
measuring the reaction temperature) and a reflux condenser.
Unless mentioned otherwise, the oxidation was carried out under
the following reaction conditions: reaction mixture = 52 mmol
benzyl alcohol + 78 mmol TBHP (70% TBHP in water) + 0.5 g
catalyst, temperature = 94 8C and reaction time = 2 h. After the
reaction, the catalyst was removed from the reaction mixture by
filtration and the reaction products and benzyl alcohol were
analyzed by gas chromatography with a flame ionization detector,
3 8 3 8
Fig. 3. XRD of U O support calcined at 400 8C (a) and Au (8.0 wt%)/U O (HDP)
using a SE-30 column and N
2
as a carrier gas. For measuring the
calcined at 100 8C (b), 300 8C (c), 400 8C (d) and 900 8C (e).
catalyst performance for the oxidation as function of time, the
liquid samples were removed intermittently from the reaction
mixture by syringe and analyzed by the GC.
3.1. Influence of the method of gold deposition
3 8
Both the surface and catalytic properties of Au/U O are
strongly influenced by the method of gold deposition on the
support (Table 1 and Fig. 4). The gold loading in case of the catalyst
prepared by the incipient impregnation method is expected to be
quantitative (i.e. 8.0 wt%). The HDP method also provides
quantitative gold deposition (8.0 wt% Au) on the support. However,
the Au loading of the catalyst prepared by the DP or CP method is
much smaller (about 60% of the available gold). The Au particle size
3
. Results and discussion
The Au/U catalysts (prepared by different methods and
3 8
O
calcined at different temperatures) were characterized for their Au
loading, surface area and Au particle size. TEM photographs of the
catalysts are shown in Figs. 1 and 2. XRD patterns of the catalyst
3 8 3 8
support (U O ) and Au/U U , prepared by the HDP method and
calcined at different temperatures (100–900 8C) are presented in
Fig. 3. The XRD patterns of the catalyst calcined at 100 8C and
3 8 3 8
of the Au/U O (HDP) is smallest while that of the Au/U O (Imp.) is
largest (Table 1). The gold particles in the catalysts prepared by the
DP and CP methods are, however, intermediate in size.
3
00 8C are almost identical. Results of the catalyst characterization
are presented in Table 1. The surface area of the Au/U (HDP)
catalyst was decreased from 12 m g to 6 m g with increasing
the Au loading from 1.1 wt% to 8.0 wt%.
3
O
8
Among the catalysts prepared by the different methods, the Au/
2
ꢀ1
2
ꢀ1
U
3
O
8
(HDP) showed the best performance (i.e. highest benzyl
alcohol conversion and benzaldehyde yield) in the benzyl alcohol
Results showing the influence of the catalyst preparation
method (viz. gold deposition on the support by DP, HDP, CP or
impregnation) on the performance of the catalyst in the oxidation
of benzyl alcohol are presented in Fig. 4. Figs. 5 and 6 show an
influence of the Au loading and calcination temperature of the Au/
3 8
U O (HDP) catalyst on its performance in the benzyl alcohol
oxidation. Influences of the process parameters (viz. reaction time
and temperature) on the benzyl alcohol oxidation over the Au/
3 8
U O (HDP) catalyst are shown in Figs. 7 and 8.
Table 1
Properties of Au/U
3
O
8
catalysts prepared by different methods.
a
Method of
Calcination
temperature
8C)
Au loading
(wt%) by
ICP
Surface
area
Particle size
of Au (nm)
preparation
2
ꢀ1
(
(m g
)
b
TEM
XRD
HDP
400
400
400
400
700
900
8.0
5.1
4.7
8.0
8.0
8.0
7
8
5
6
6
5
9.4
15.5
16
11.5
17.2
17.5
38.4
22.4
34.3
DP
Co-precipitation
Impregnation
HDP
34.1
20.3
32.3
HDP
3 8
Fig. 4. Performance of Au/U O catalysts prepared by different gold deposition
a
Amount of gold available for its deposition on support = 8.0 wt% of the support.
methods and calcined at 400 8C in the oxidation of benzyl alcohol (amount of
catalyst = 0.5 g, reaction temperature = 94 8C and reaction time = 2 h).
b
From peak broadening of Au (2 0 0) peak (2u= 38.58).

V.R. Choudhary, D.K. Dumbre / Applied Catalysis A: General 375 (2010) 252–257
255
Fig. 7. Influence of reaction temperature on the performance of benzyl alcohol by
TBHP to benzaldehyde over Au (8 wt%)/U (HDP) 400 8C (reaction time = 0.5 h).
3 8
O
Fig. 5. Influence of the Au loading of Au/U
the benzyl alcohol oxidation (amount of catalyst =0.5 g, reaction temperature
94 8C and reaction time = 2 h).
3
O
8
(HDP) catalyst on its performance in
3 8
The Au/U O (HDP) showed excellent reusability in the benzyl
alcohol oxidation; in the 1st, 3rd and 5th reuse of the catalyst, the
benzyl alcohol conversion was 100% with benzaldehyde selectivity
of 84%, 82% and 83%, respectively.
=
3 8
Since the Au/U O catalyst prepared by the HDP method
oxidation; the order of catalysts for their performance is as follows:
Au/U (HDP) > Au/U (DP) > Au/U (CP) > Au/U (Imp.)
Fig. 2). This is consistent with the earlier studies which showed
that the MgO, Yb or TiO supported nano-gold catalyst
prepared by the HDP method) showed superior performance in
the epoxidation of styrene [27–29].
The Au/U (HDP) and Au/U
8.0 wt% Au) but the latter showed significantly poorer catalytic
performance because of its larger Au particle size (Table 1). The
Au/U (DP or CP) showed intermediate catalytic performance
showed the best catalytic performance and excellent reusability,
further detailed investigations on this catalyst were undertaken
(described below).
3
O
8
3
O
8
3
O
8
3 8
O
(
2
O
3
2
(
3
O
8
3 8
O (Imp.) have similar Au loading
(
3 8
O
mostly because of its intermediate Au particle size and lower Au
loading.
Fig. 6. Influence of calcination temperature of Au (8 wt%)/U
3
O
8
(HDP) on its
Fig. 8. Influence of reaction time and catalyst concentration on the performance of
performance in the oxidation of benzyl alcohol (amount of catalyst = 0.5 g, reaction
Au (8 wt%)/U
3 8
O (HDP) catalyst in the oxidation of benzyl alcohol (reaction
temperature = 94 8C and reaction time = 2 h).
temperature = 94 8C).

2
56
V.R. Choudhary, D.K. Dumbre / Applied Catalysis A: General 375 (2010) 252–257
Table 2
Comparison of different heterogeneous catalysts for their performance in solvent-free liquid-phase benzyl alcohol-to-benzaldehyde oxidation by different oxidizing agents.
Catalyst
Oxidizing
agent
Reaction conditions
Temperature Pressure
Alcohol
BZH
Productivity
Reference
conversion (%)
yield (%)
of BzH (mmol/g(cat)/h)
Time
(h)
Amount of
b
(
8C)
(atm)
catalyst (g/mol)
a
Ni–Al–HT
O
O
O
O
O
O
2
2
2
2
2
2
90
1.0
1.0
1.5
10
12.0
5.0
5.0
0.5
8.0
8.0
2.0
5.0
1.0
0.5
2.0
0.5
250
5.2
3.4
0.3
–
–
51.0
53.0
1.9
31.0
35.7
50.4
1.6
0.1
13.8
[10]
Cu–Cr–HT
Au/U
Au–Pd/TiO
Au–Pd/Al
Au/TiO
S-S–Cr(III)–HT
210
130
100
100
100
50
[13]
3
O
8
29.0
[20,21]
[23]
2
105.0
174.0
240.0
54.8
2
O
3
2
83.3
15.3
65.8
50.2
55.0
100
63.1
100
72.1
9.8
[22]
2
2
–
[22]
c
H
2
O
2
1.0
1.0
1.0
1.0
1.0
1.0
6.0
9.6
9.6
9.6
9.6
1.9
65.8
50.0
50.6
72.5
50.0
85.0
[24]
ꢀ1
MnO
4
-HT
TBHP
TBHP
TBHP
TBHP
TBHP
94
10.4
[12]
Co–Cr–LDH
Au/MgO
70
52.7
[14]
94
150.8
26.0
[30]
Au/TiO
2
94
[31]
Au/U
3
O
8
94
884
Present work
a
In the presence of toluene as a solvent.
b
c
Weight in grams per mole of benzyl alcohol.
Sulphonato-salen–Cr(III) hydrotalcite, HT = hydrotalcite.
3
.2. Influence of Au loading in Au/U
3
O
8
(HDP)
performance are presented in Figs. 7 and 8. Both the benzyl alcohol
conversion and the product selectivities are strongly influenced by
the reaction temperature, depending upon the reaction time
(Fig. 7). As expected, the conversion increased exponentially when
the reaction temperature was increased. However, the selectivity
for benzaldehyde decreased and consequently that of benzyl
benzoate also increased with increasing temperature. The influ-
ence of the reaction temperature is found to be very large above the
temperature of 60 8C.
The results in Fig. 5 show a strong influence of the Au loading on
the performance of benzyl alcohol oxidation.
As expected the conversion of benzyl alcohol increased with
increasing Au loading; the increase was almost linear. However,
the benzaldehyde selectivity decreased from 100% to 83% with
increasing Au loading (0.0–8.0 wt%). The selectivity for benzyl
benzoate showed the exactly opposite trend. The formation of
benzoic acid was negligibly small. The support (U
a little benzyl alcohol oxidation activity (<10% conversion of
benzyl alcohol, mainly to benzaldehyde).
3
O
8
) showed only
As expected the benzyl alcohol conversion increased with
increasing reaction time and the time required for completing the
benzyl alcohol oxidation was longer when a smaller amount of
catalyst was used (Fig. 8). The selectivity for benzaldehyde is,
however, decreased continuously with increasing reaction time.
The exactly opposite trend is observed for the benzyl benzoate
selectivity. The observed selectivity trends reveal the occurrence of
following consecutive reactions in the benzyl alcohol oxidation:
On increasing the Au loading from 1.1 wt% to 8.0 wt%, the
2
ꢀ1
surface area of the catalyst decreased continuously from 12 m g
2
ꢀ1
to 6 m g . The decrease in the surface area is expected mostly
because of the adsorption of increasing amounts of chloride
species on the catalyst support during the Au deposition for the
higher gold loading in the catalyst.
C
6
H
5
ꢀCH
2
OH þ ðCH
3
Þ
3
COOH ! C
6
H
5
ꢀCHO þ ðCH
3
Þ
3
COH þ H
2
O
3.3. Influence of catalyst calcination temperature
(1)
The performance of the Au (8.0 wt%)/U (HDP) in the benzyl
3
O
8
C
6
H
5
ꢀCHO þ ðCH
3
Þ
3
COOH ! C
6
H
5
ꢀCOOH þ ðCH
3
Þ
3
COH þ H
2
O
alcohol oxidation is strongly influenced by its calcination
temperature (Fig. 6). The benzyl alcohol conversion and benzalde-
hyde selectivity passed through a maximum and a minimum,
respectively, with increasing calcination temperature. The change
in the conversion is very large but that in the selectivity is
relatively small. The benzaldehyde yield also passed through a
maximum with increasing calcination temperature, indicating an
optimum calcination temperature (400 8C) for the catalyst
performance. The poor performance of the catalyst when it was
calcined below 400 8C may be due to the presence of moisture in
the catalyst. The sharp decrease in the oxidation activity of the
catalyst, when calcined at higher than optimum temperature (i.e.
above 400 8C), is mostly because of the growth (or sintering) of the
gold particles. It may be noted that the Au particle size is increased
from 9.4 nm to 32.3 nm with increasing the catalyst calcination
temperature from 400 8C to 900 8C (Table 1). Our earlier studies
(
2)
C
6
H
5
ꢀCOOH þ C
6
H
5
ꢀCH
2
OH ! C
6
H
5
ꢀCOOCH
2
C
6
H
5
þ H
2
O
(3)
The formation of benzoic acid in the process was negligibly
small and hence reaction (3) over the catalyst is expected to be
quite fast.
3 8
3.5. Comparison of Au/U O (HDP) with earlier catalysts
The performance (benzaldehyde productivity or turn over rate
3 8
in solvent-free benzyl alcohol oxidation) of the Au (8.0 wt%/U O
(HDP)) catalyst is compared with that of the earlier reported active
solid catalysts for the process in Table 2.
3 8
It may be noted that the Au/U O (HDP) catalyst while using
TBHP as the oxidizing agent (at 94 8C) showed highest productivity
[0.9 mol/g(cat)/h], even at 100% conversion of benzyl alcohol, and
very high yield (85%) for benzaldehyde. It is also noteworthy that
the same catalyst while using molecular oxygen as an oxidizing
agent showed much lower benzaldehyde productivity [0.03 mol/
g(cat)/h] and yield (50%), even at a higher temperature (130 8C)
[
21] showed that the calcination temperature of the catalyst for its
optimum performance in the oxidation of benzyl alcohol to
benzaldehyde by molecular oxygen was also 400 8C.
3
.4. Influence of reaction conditions
[
21].
The Au/MgO and Au/U
loadings (7.5 wt% and 8.0 wt%, respectively) and Au particle sizes
Results showing the influence of the reaction temperature, the
time and also that of the amount of catalyst used on the process
3 8
O catalysts have almost the same Au

V.R. Choudhary, D.K. Dumbre / Applied Catalysis A: General 375 (2010) 252–257
257
[
[
[
2] S. Tsuruya, H. Miyamoto, T. Sakae, M. Masai, J. Catal. 64 (1980) 260–271.
(
3 8
9.0 nm and 9.4 nm, respectively). However, the Au/U O catalyst
3] H. Hayashibara, S. Nishiyama, S. Tsuruya, M. Masai, J. Catal. 153 (1995) 254–264.
4] S.J. Kulkarni, R.R. Rao, M. Subramanyam, A.V. Ramarao, A. Sarkany, L. Guczi, Appl.
Catal. A: Gen. 139 (1996) 59–74.
showed much better performance in the benzyl alcohol-to-
benzaldehyde oxidation (Table 2). This indicates the important
role played by catalyst support in controlling the catalytic activity
of supported gold catalyst through nano-gold particle–support-
interactions.
[
[
5] S. Sueto, S. Nishiyama, S. Tsuruya, M. Masai, J. Chem. Soc., Faraday Trans. 93 (1997)
659–664.
6] R. Sumathi, K. Johnson, B. Vishwanthan, T.K. Varadarajan, Appl. Catal. A: Gen. 172
(1998) 15–22.
For many years, uranium-based catalysts have been used in
industrial practice and the procedures for their safe handling are
well established [32]. However, since uranium is radioactive, long
time exposure and/or inhalation of dust of uranium oxide should
be avoided.
[7] N. Idaki, S. Nishiyama, S. Tsuruya, Phys. Chem. Chem. Phys. 3 (2001) 1918–1924.
[8] L.F. Liotta, A.M. Venezia, G. Deganello, A. Longo, A. Martorana, Z. Schay, L. Guczi,
Catal. Today 66 (2001) 271–276.
[9] M.J. Schultz, C.C. Park, M.S. Sigman, Chem. Commun. (2002) 3034–3035.
[10] B.M. Choudary, M.L. Kantam, A. Rahman, C.V. Reddy, K.K. Rao, Angew. Chem. Int.
Ed. Engl. 40 (2001) 763–766.
11] G.D. Yadav, C.K. Mistry, J. Mol. Catal. A: Chem. 172 (2001) 135–149.
12] V.R. Choudhary, D.K. Dumbre, V.S. Narkhede, S.K. Jana, Catal. Lett. 86 (2003) 229–
233.
[
[
4
. Conclusions
[
[
13] V.R. Choudhary, P.K. Choudhary, V.S. Narkhede, Catal. Commun. 4 (2003) 171–
175.
3 8
Nano-gold deposited on U O by the homogeneous deposition
14] V.R. Choudhary, D.K. Dumbre, B.S. Uphade, V.S. Narkhede, J. Mol. Catal. A: Chem.
215 (2004) 129–135.
15] M. Haruta, Cattech 6 (2002) 102–107.
precipitation method shows very high catalytic activity, selectivity
and productivity and also shows excellent reusability in the
solvent-free oxidation of benzyl alcohol to benzaldehyde by TBHP
under mild reaction conditions. TBHP is a preferred oxidizing agent
while using this catalyst in the benzyl alcohol-to-benzaldehyde
oxidation for achieving 100% benzyl alcohol conversion (with very
good benzaldehyde selectivity) in a short reaction period. The
catalytic activity and selectivity are strongly influenced by the gold
loading and the calcination temperature of the catalyst. The
catalyst prepared by the DP, CP or impregnation method, however,
showed inferior performance in the process.
[
[
16] C. Milone, R. Ingoglia, G. Neri, A. Pistone, S. Galvagno, Appl. Catal. A: Gen. 211
(
2001) 251–257.
[17] C. Milone, R. Ingoglia, A. Pistone, G. Neri, S. Galvagno, Catal. Lett. 87 (2003) 201–
09.
18] S. Biella, L. Prati, M. Rossi, IV World Congress on Oxidation Catalysis, Berlin, 2001
pp. 371–375).
2
[
(
[19] S. Biella, M. Rossi, Chem. Commun. (2003) 378–379.
[20] V.R. Choudhary, A. Dhar, P. Jana, B.S. Uphade, Green Chem. 7 (2005) 768–770.
21] V.R. Choudhary, R. Zha, P. Jana, Green Chem. 9 (2007) 267–272.
22] D.I. Enache, J.K. Edward, P. Landon, B. Solsana-Esprine, A.F. Carley, A.A. Herging, M.
Wanatabe, C.J. Kiely, D.W. Knight, G.J. Hutching, Science 311 (2006) 362–365.
[
[
[23] D.I. Enache, D. Barker, J.F. Edwards, S.H. Tayloo, D.W. Knight, A.F. Carley, G.J.
Hutchings, Catal. Today 122 (2007) 407–411.
[
[
[
24] G. Wu, X. Wang, J. Li, N. Zhao, W. Wu, Y. Sun, Catal. Today 131 (2008) 402–407.
25] D.K. Dumbre, PhD Thesis, University of Pune, Pune, 2008.
26] G.H. Hutchings, C.S. Heneghan, I.D. Hudson, S.H. Taylor, Nature 384 (1996) 341–
Acknowledgements
3
43.
27] N.S. Patil, B.S. Uphade, P. Jana, S.K. Bhargava, V.R. Choudhary, J. Catal. 223 (2004)
36–239.
[28] N.S. Patil, B.S. Uphade, P. Jana, S.K. Bhargava, V.R. Choudhary, Chem. Lett. 33
2004) 400–401.
VRC and DKD are grateful to the National Academy of Sciences,
India, for the NASI Senior Scientist Platinum Jubilee Fellowship and
Project Assistantship, respectively, and also to the CMC group (NCL,
Pune) for help in the catalyst characterization.
[
2
(
[
29] N.S. Patil, B.S. Uphade, P. Jana, R.S. Sonawane, S.K. Bhargava, V.R. Choudhary, Catal.
Lett. 94 (2004) 89–93.
References
[30] V.R. Choudhary, D.K. Dumbre, Catal. Commun. 10 (2009) 1738–1742.
31] V.R. Choudhary, D.K. Dumbre, S.K. Bhargava, I&EC Res. 48 (2009) 9471–9478.
[
[
1] J.L. Kroschwitz, 4th ed., Encyclopedia of Chemical Technology, vol. 4, Wiley-
Interscience Publications, New York, 1992.
[32] J.L. Callahan, R.K. Grasselli, E.C. Miberger, R.A. Strecher, Ind. Eng. Chem. Prod. Res.
Dev. 6 (1970) 134–139.