Polymer impregnated sulfonated carbon composite solid acid catalyst for alkylation of phenol with methyl-tert-butyl ether

Article abstract of DOI:10.1039/c4ra11033a

A polymer impregnated sulfonated carbon composite solid acid (P-C-SO₃H) catalyst was synthesized via sulfonation of a composite material formed through incomplete carbonization of hydrolyzed glucose supported on a polymer matrix (co-polymer of styrene and chloromethylstyrene i.e. Merrifield's peptide resin) and used for the alkylation of phenol using methyl-tert-butyl ether (MTBE) as an alkylating agent in a pressure reactor under autogenous pressure. The developed catalyst exhibited excellent catalytic activity and provided para-tert-butyl phenol (PTBP) exclusively with the added benefits of facile recovery and reusability for several runs without loss of catalytic activity.

Full text of DOI:10.1039/c4ra11033a

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Polymer impregnated sulfonated carbon
composite solid acid catalyst for alkylation of
Cite this: RSC Adv., 2015, 5, 3286
phenol with methyl-tert-butyl ether†
Praveen K. Khatri, Manvi Manchanda, Indrajit K. Ghosh and Suman L. Jain*
3
A polymer impregnated sulfonated carbon composite solid acid (P–C–SO H) catalyst was synthesized via
sulfonation of a composite material formed through incomplete carbonization of hydrolyzed glucose
supported on a polymer matrix (co-polymer of styrene and chloromethylstyrene i.e. Merrifield's peptide
resin) and used for the alkylation of phenol using methyl-tert-butyl ether (MTBE) as an alkylating agent in
a pressure reactor under autogenous pressure. The developed catalyst exhibited excellent catalytic
activity and provided para-tert-butyl phenol (PTBP) exclusively with the added benefits of facile recovery
and reusability for several runs without loss of catalytic activity.
Received 23rd September 2014
Accepted 1st December 2014
DOI: 10.1039/c4ra11033a
www.rsc.org/advances
phenols, leads to the formation of phenol by-products, such as
Introduction
13,14
derivatives having a secondary butyl substitute.
Thus, it is
p-tert-Butyl phenol (PTBP) is a stable and readily biodegradable advantageous to use MTBE as an alkylating agent which
chemical which is being widely used as an intermediate for generates pure isobutylene in situ and the co-product methanol
1,2
phenol resins and polycarbonate resins. It is also used as a can be easily recovered and recycled.
raw material for construction elements and oors in buildings.
Owing to the growing environmental considerations, the use
Additionally t-butylated phenols (TBPs) have extensively been of solid acid catalysts is preferred as they can easily be recov-
used as precursors or starting materials in a variety of industries ered, recycled and can eliminate the problems associated with
including pharmaceuticals. For instance, the product o-tert- the highly corrosive and polluting homogeneous liquid acid
15–19
butylphenol (OTBP) is an intermediate for pesticides, catalysts.
Heterogeneous acid catalysts studied so far for the
fragrances and other products, whereas PTBP is used as a raw tert-butylation of phenol using MTBE as an alkylating agent
2
0
7,21–23
material for the production of a variety of resins, phosphate include cation-exchange resins, zeolites,
clay-based cata-
24
25–27
esters, durable surface coatings, varnishes, wire enamels, lysts and mesoporous molecular sieves.
Cation-exchange
fragrances, oil eld chemicals and demulsiers. 2,4-Di-tert- resins owing to their easy availability and low cost have been
butylphenol (DTBP) is an intermediate for antioxidants and 2,6- considered to be most promising, however, the physical
di-tert-butylphenol is used as an antioxidant intermediate and strength of the ion exchange resins is lowered at a high
3
–12
in pharmaceuticals.
Conventional processes for producing temperature and therefore, the reaction must be carried out at
ꢀ
tert-butyl phenols (TBPs) from an isobutylene-containing C
4
lower temperature (100–120 C) that lead to the poor yield of the
3
raffinate stream typically involve introducing methanol, or desired 4-TBPs. Recently sulfonated carbons (C–SO H) derived
another alcohol, into the C stream to react and produce alkyl from the incomplete carbonization of simple sugars such as
4
tertiary butyl ether intermediate that is further decomposed to glucose has come out to be a new class of catalysts exhibiting
make high-purity isobutylene, which can then be reacted with excellent catalytic performance for acid catalyzed reactions such
28
phenol to produce the tert-butyl phenol. The additional step of as biodiesel synthesis. Recently, Goodwin et al. reported a
adding methanol signicantly increases the costs of producing novel polymer impregnated sulfonated carbon based solid acid
tert-butyl phenols and creates another undesirable byproduct. catalysts for esterication reactions. Inspired with this report,
Besides the additional expenses, the additional byproducts are we thought it would be worthwhile to explore the potential of
unattractive for environmental reasons. Isobutylene may also be such catalysts for other industrially important acid catalyzed
produced by isobutanol dehydration. However, in this case an reactions. Accordingly, herein we report an efficient polymer
impure product may form which, when used for alkylating impregnated sulfonated carbon composite solid acid catalyst
for the alkylation of phenol using MTBE as an alkylating agent
in a pressure reactor under autogenous pressure. The reaction
Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Dehradun-248005,
was found to be highly regioselective and afforded PTBP selec-
India. E-mail: suman@iip.res.in; Fax: +91-135-2660202; Tel: +91-135-2525788
tively in excellent yield.
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4ra11033a
1
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+
and 1.36 mmol H per g for C–SO
3
H) in comparison to the
Results and discussion
Synthesis and characterization of the catalyst
estimated values obtained from elemental sulfur analysis data.
This discrepancy in results may be due to the generation of
During the present study, the targeted polymer impregnated phenolic-OH and –COOH groups by incomplete carbonization
30,31
sulfonated carbon (P–C–SO
3
H) was synthesized via sulfonation of glucose.
3
The higher acidity of P–C–SO H catalyst is most
of a composite material formed through incomplete carbon- likely due to the presence of evenly distributed polycyclic
ization of hydrolyzed glucose supported in a polymer matrix aromatic hydrocarbons along to the resin framework which may
based on a copolymer of styrene and chloromethylstyrene i.e. lead to the greater availability of active sites for sulfonation and
Merrield resin (Scheme 1). For the comparative study, the resulted to the higher acid density of P–C–SO
3
H as compared to
H. The BET surface areas along with the
H-acid site densities of the synthesized catalysts are given in
H) was prepared the Table 1.
28
corresponding sulfonated carbon catalyst (C–SO H) was the C–SO H and P–SO
3 3
3
prepared via incomplete carbonization of glucose and a SO
polymer-based catalyst without carbon (P–SO
3
3
by the sulfonation of the incompletely carbonized Merrield
resin.
Thermal stability of the synthesized sulfonated catalysts was
determined by thermal gravimetric analysis (TGA). As shown in
Fig. 1, the initial weight loss (about 5%) below 150 C in all three
ꢀ
The powder X-ray diffraction of the synthesized P–C–SO
3
H
catalyst did not show any characteristic peak and exhibited a catalysts was mainly due to the loss of a small amount of
ꢀ
broad peak centered at 2q value of 25 , indicating that the adsorbed water. The weight loss process of P–C–SO
3
H and
ꢀ
synthesized material is amorphous in nature (Fig. S1†).
FT-IR spectra of the synthesized P–C–SO H and C–SO
C–SO
3
H below 150 C was found to be similar, however at
ꢀ
higher temperatures (>300 C) P–C–SO H showed a plateau
3
3
3
H
catalysts are shown in Fig. S2.† A broad absorption band indicating a much slower rate of weight loss as compared to that
À1
around 3300 cm in P–C–SO
3
H obtained aer sulfonation of C–SO
3
H, which is mainly due to the gradual desorption and
was attributed to OH stretching with two shoulder peaks due thermal decomposition process of polymer framework (Fig. 1).
to the aromatic C–H and aliphatic C–H stretching. The band However, the thermogravimetric curve of P–SO H showed a
3
À1
ꢀ
around 1630–1780 cm
corresponding to the overlapped signicant weight loss in the range of 350–550 C due to the
C]O and S]O stretching was stronger in P–C–SO H catalyst degradation of polymer framework (Fig. 1). Finally a rapid
3
ꢀ
than in C–SO H, most likely due to the higher loading of the weight loss was occurred in the temperature range 550 to 650 C
3
acid sites in the polymer impregnated carbon catalyst. The when no mass was le at this temperature.
poor acidity of carbon (C–SO
a very weak band around 1200 cm corresponding to the
asymmetric and symmetric stretching of sulfonic acid groups.
3
H) catalyst was further proved by
À1
This peak was found to be quite stronger in P–C–SO
lyst. Furthermore, a sharp absorption band near to 600 cm
3
H cata-
3
Table 1 BET-surface area and SO H-acid densities of the sulfonated
catalysts
À1
corresponding to C–Cl and C–S stretching was appeared in
a
b
BET surface area
S-content
(mmol g
Total acid density
(mmol H per g)
P–C–SO H.
3
2
À1
À1
+
Catalyst
(m g
)
)
Sulfur contents or SO
C–SO H and P–SO H catalysts were estimated by elemental P–C–SO H
analysis. The acidity of the P–C–SO
calculated from elemental sulfur analysis by assuming that all
the sulfur atoms in the catalyst are presented in –SO H form
3 3
H-acid densities in P–C–SO H,
3
3
3
<1
<1
<1
2.44
1.28
1.52
2.54
1.36
1.53
H, C–SO
3
H and P–SO
3
H
C–SO
3
H
H
3
P–SO
3
a
b
3
Determined by elemental analysis.
Determined by acid–base
+
titration method (dried catalyst (0.1 g) was treated with aq. NaOH
0.004 N, 30 ml) for 0.5 h at room temperature under stirring. Aer
that a pH titrator was used to neutralize excess NaOH with 0.02 N HCl).
were found to be 2.44, 1.28 and 1.52 mmol H per g respectively.
In addition, the total acidity of the synthesized catalysts was
(
29
determined using standard acid–base back titration method.
The acid site densities as calculated by titration method were
+
3
found to be slightly higher (2.54 mmol H per g for P–C–SO H
Scheme 1 Formation of P–C–SO
3
H, P–SO
3
H and C–SO
3
H.
3 3 3
Fig. 1 TGA of P–C–SO H, C–SO H and P–SO H.
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the subsequent run (Table 2, entry 14). The higher reactivity of
P–C–SO H compared to that of other two sulfonated catalysts
3
can be explained on the basis of its higher SO H acid site
3
densities. Based on these ndings, we have chosen P–C–SO H
3
catalyst for the further studies.
In order to nd out the best reaction conditions with
P–C–SO H catalyst a number of controlled experiments were
3
Scheme 2 Alkylation of phenol with MTBE.
performed under different reaction conditions. The results of
these experiments are summarized in Table 2 (entries 1–12).
The reaction temperature was found to be a key parameter for
alkylation of phenol with respect to the selectivity of the desired
p-tert-butyl phenol (PTBP) as shown in Table 2, entries 1–6).
Catalytic activity
3 3
The catalytic activity of the synthesized P–C–SO H, C–SO H and
P–SO H catalysts was checked for the alkylation of phenol with
3
MTBE in a high pressure reactor under autogenous pressure to
give tert-butyl phenol derivatives. A general reaction scheme for
the alkylation of phenol is shown in Scheme 2.
Isobutylene thus generated from the acid catalyzed cracking
of MTBE reacts with phenol and gave tert-butyl phenols such as
o-tert-butyl phenol (OTBP), p-tert-butyl phenol (PTBP) and 2,4-
di-tert butyl phenol (2,4-DTBP) without any evidence for the
formation of 2,6-di-tert-butyl phenol and any other side product
which may produce by oligomerization of isobutylene. The
results of these experiments are given in Table 2. As shown,
among all three catalysts studied, polymer impregnated
ꢀ
When the reaction was performed at 110 C under otherwise
identical conditions, the selectivity of PTBP was very low. The
selectivity of PTBP was appreciably improved with increasing
ꢀ
the temperature from 120 to 140 C (entries, 2–4). Further
ꢀ
ꢀ
increase of temperature from 150 C to 160 C (entry 5 and 6)
did not show any noticeable boost in the selectivity of PTBP.
ꢀ
Based on these ndings 140 C was considered to be optimum
reaction temperature for this reaction at which maximum yield
of PTBP was obtained. Similarly the amount of catalyst had
pronounced effect on the conversion of phenol (Table 1, entries
4, 7–9). It was noticed that the conversion of phenol was
signicantly increased with increasing the catalyst quantity
from 1 to 5 wt% (entries 4, 7–8). The maximum conversion of
phenol was achieved (i.e. 96%) at 5 wt% of the catalyst and
beyond this no signicant change in the conversion of phenol
was obtained (entry 9). All the experiments were carried out by
using the molar ratio of phenol and MTBE as 1 : 1. An increase
in molar ratio of phenol to MTBE from 2 to 5 did not show any
signicant improvement in the conversion of phenol and
sulfonated carbon (P–C–SO H) catalyst was found to be superior
and gave excellent conversion of phenol with the formation of p-
tert-butyl phenol as the predominant product (Table 2, entry 4).
In case of C–SO H, the reaction rate was found to be very slow
3
and gave only 10% conversion with the 62% selectivity for the
PTBP (Table 2, entry 13). The sulfonated polymer based catalyst
3
3 3
(P–SO H) showed comparable initial activity as P–C–SO H for
the alkylation of phenol but lost about 20% of its activity in
a
Table 2 Acid catalyzed tert-butylation of phenol
c
Selectivity of product (%)
Molar ratio
(PhOH + MTBE)
ꢀ
b
Entry
T/( C)
Cat. (wt%)
Conv. (%)
OTBP
PTBP
2,4-DTBP
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1 : 1
1 : 1
1 : 1
1 : 1
1 : 1
1 : 1
1 : 1
1 : 1
1 : 1
1 : 2
1 : 5
2 : 1
1 : 1
1 : 1
1 : 1
1 : 1
1 : 1
110
120
130
140
150
160
140
140
140
140
140
140
140
140
140
150
160
5
5
5
5
5
5
1
3
7
5
5
5
5
5
93
93
95
96
96
96
82
89
95
96
95
94
10
15
17
17
5
5
6
13
5.5
7
5
6
8
12
14, 18
5, 15, 18
6
5
36
42
48
80
81
80
61
68
80
79
80
66
44
36
31
15
13
12
18
26.5
13
16
14
20
26
0
1
2
3
4
5
6
7
d
62
e
f
80, 58
96 , 30 , 89
95
96
66, 62
80, 72, 68
79
20
g,h,i
g
h
i
1.46 mmol SO
5
5
3
H
15, 13, 14
15
14
j
j
81
a
b
c
d
e
Catalyst P–C–SO
3
H; reaction time 2 h. Determined by GC and GCMS. Determined by GC and GCMS. Using C–SO
3
H as catalyst. Using
f
g
h
P–SO
3
H catalyst. Recycling of the P–SO
3
H catalyst. Using similar reactant/catalytic acid site ratio (P–C–SO
3
H). Using similar reactant/
i
j
ꢀ
catalytic acid site ratio (C–SO
the reactant.
3
H). Using similar reactant/catalytic acid site ratio (P–SO
3
H). Using the reaction mixture obtained at 110 C as
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3 3
selectivity of PTBP or in product distribution ratio (entries 10– stability of –SO H groups due to the desulfonation in C–SO H
11). Similarly, no further improvement was observed when 2 : 1 catalyst.
molar ratio of phenol and MTBE was used (Table 2, entry 12).
Apart from the comparative studies based on same wt% of all
three catalysts, we also performed the comparison using same
phenol/MTBE/catalytic site molar ratio. Considering that all the
Experimental
Reagents used
sulfur is presented in the form of –SO
mmol –SO H, which is equivalent to the (0.6 g of P–C–SO
.14 g of C–SO H and 0.96 g of P–SO H when 1 : 1 molar ratio of Aldrich), acetonitrile (CH CN, 99.9%, Acros Organics), conc.
3
H, we have used 1.46 Reagents including D-glucose (reagent grade, Aldrich), Merri-
3
3
H, eld's peptide resin, 1% cross linked, 100–200 mesh (Sigma-
1
3
3
3
phenol and MTBE was used). The results of these experiments sulfuric acid (99.7%, Aldrich) were used as received.
are summarized in Table 2 (entry 15). As shown, the higher
activity of all the catalysts might be due to the presence of nearly
equal active catalytic acid sites. However, the superiority of the
Preparation of the polymer impregnated-SO H functionalized
carbon composite
3
P–C–SO
loading and stability of –SO
3
H catalyst can be explained on the basis of higher
H groups without showing any
3
Polymer impregnated –SO H containing carbon composite
3
(
P–C–SO H) was synthesized by the pyrolysis of a polymer
3
leaching during the reaction. Moreover we also performed the
matrix impregnated with D-glucose and followed by its sulfo-
nation with conc. sulfuric acid as depicted in Scheme 1. In a
typical experiment, a solution of D-glucose (2.0 g) in 3 ml of
ꢀ
experiments using the reaction mixture obtained at 110 C as
the reactant for the alkylation at higher temperatures i.e. 150
ꢀ
and 160 C under otherwise identical experimental conditions
2 4
deionized water was added with 2 drops of sulfuric acid (H SO )
(Table 2, entries 16–17). The product distribution ratio was
and the resulting mixture was slowly added to a pre dried
Merrield's peptide resin (2 g) with magnetic stirring. Aer
complete addition of glucose solution, the resulting mixture
remained almost similar to that of using fresh reactants.
Multiple recycling experiments were performed to examine
the reusability and the stability of the –SO
3
H groups in the
ꢀ
was dried at 110–120 C for 12 h. Thus obtained black material
polymer composite catalyst (P–C–SO H). At the end of the
3
was crushed to powder and then pyrolyzed under dry nitrogen at
reaction, the catalyst was recovered by simple ltration and
reused for the subsequent alkylation of phenol with MTBE
under described reaction conditions. The recycling of the
recovered catalyst was tested for six runs (Fig. 2). In these
experiments the conversion of phenol and selectivity for PTBP
remained as good as with the fresh catalyst, indicating that the
synthesized catalyst is highly stable and can be reused for
several runs. Furthermore, the sulfur content of the recovered
catalyst obtained aer six runs was found to be almost similar
to the fresh one. These results suggested the higher stability of
the SO H groups in P–C–SO H and conrmed that the devel-
ꢀ
3
00 C for 1 h in a muffle furnace.
The resulting black residue was subjected to sulfonation by
using concentrated sulfuric acid (1 g solid/20 ml H
2
SO
4
) at
ꢀ
160 C for 12 h under nitrogen atmosphere. The mixture was
diluted with plenty of distilled water and the black material so
obtained was collected by ltration, washed several times with
ꢀ
hot distilled water of 80 C until impurities like sulfate ions
were no longer detected in the wash water. The resulting black
ꢀ
solid (P–C–SO
3
H) was dried in an oven at 80 C under vacuum
for 5 h and subsequently used for the alkylation of phenol with
MTBE. For the comparative studies, a sulfonated polymer based
3
3
oped catalyst is truly heterogeneous in nature. To compare the
stability of –SO H groups, we also checked the recycling ability
of C–SO H catalyst under similar reaction conditions. The
3
solid acid (P–SO H) catalyst was prepared via direct sulfonation
3
of Merrield peptide resin and sulfonated carbon catalyst (C–
3
SO
3
H) was synthesized by the heating of D-glucose powder (10 g)
catalyst exhibited almost negligible activity for the second run
and gave <2% conversion of phenol. Furthermore, signicantly
lower sulfur content in the recovered catalyst indicating the less
ꢀ
at 400 C for 1 h under dry N2 atmosphere by incomplete
carbonization. The resulting black material was crushed to
powder and then subjected to sulfonation with conc. H
2 4
SO .
Sulfonated polymer matrix (P–SO H) was prepared by heating of
3
ꢀ
ꢀ
Merrield's peptide resin at 300 C for 1 h under dry N
2
, fol-
lowed by its sulfonation at 160 C for 13 h under a dry N
atmosphere.
2
General procedure for the alkylation of phenol
The alkylation experiments were carried out in a stainless steel
batch reactor of 25cc and 100cc by varying the reaction
parameters under autogenous pressure conditions. In a typical
experiment phenol (6.2 g, 66 mmol) and MTBE (5.8 g, 66 mmol)
in a 1 : 1 molar ratio and catalyst P–C–SO H (5 wt% of the total
3
weight of reactants) were charged into a 100cc parr autoclave.
ꢀ
The mixture was heated at 140 C for 2 h under stirring. At the
end of the reaction, the vessel was cooled down to room
Fig. 2 Recycling experiments red bar indicates the conversion of
phenol and green bar is attributed to the selectivity of PTBP.
temperature and the catalyst was separated by ltration. The
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recovered catalyst was washed with methanol, dried and used 10 S. Sumbramanian, A. Mitra, C. V. V. Satyanarayana and
for the recycling experiments. Filtrate so obtained was diluted D. K. Chakrabarty, Appl. Catal., A, 1997, 159, 229.
with acetonitrile and subjected for gas chromatography (GC) 11 S. H. Patinuin and B. S. Friedman, in Alkylation of aromatics
and GCMS analysis to determine the conversion and the selec-
tivity of the TBPs as shown in Table 2.
with alkenes and alkanes in Friedel Cras and related reactions,
ed. G. A. Olah, Interscience, New York, 1964, vol. 3, p. 75.
2 I. F. Lorenc, G. Lambeth and W. Scheffer, in Kirk-Othmer
Encyclopedia of Chemical Technology, ed. M. Howe-Grant
and J. I. Kroschwitz, Wiley, New York, 1992, vol. 2, p. 113.
1
Conclusion
In summary, we have demonstrated a highly efficient solid acid 13 G. D. Yadav and N. Kirthivasan, in Fundamental and Applied
catalyst, easily prepared via sulfonation of a polymer impreg-
Aspects of Chemically Modied Surfaces, ed. J. P. Blitz and C.
nated carbon composite for alkylation of phenol using MTBE as
B. Little, Royal Society of Chemistry, UK, 1999, pp. 254–269.
the alkylating agent under mild experimental conditions. The 14 G. D. Yadav, A. A. Pujari and A. V. Joshi, Green Chem., 1999, 1,
reaction was found to be highly selective and afforded p-tert-
269.
butyl phenol predominantly in excellent yield. The developed 15 A. A. Carlton, J. Org. Chem., 1948, 13, 120.
polymer impregnated carbon based solid acid was found to be 16 P. Elavarasan, K. Kondamudi and S. Upadhyavula, Chem.
superior in terms of both activity and stability in comparison to
the sulfonated carbon (C–SO H) and sulfonated polymer 17 Y. G. Li, B. Xue and Y. T. Yang, Fuel Process. Technol., 2009,
P–SO H) catalyst. The prepared catalyst could easily be recov-
90, 1220–1225.
ered and recycled for several runs without any signicant loss in 18 L. Ronchin, A. Vavasori and L. Toniolo, J. Mol. Catal. A:
activity. No leaching of active –SO H groups was observed as
Chem., 2012, 355, 134–141.
evidenced from elemental sulfur analysis of recovered catalyst 19 G. D. Yadav and G. S. Pathre, Microporous Mesoporous Mater.,
Eng. J., 2011, 166, 340–347.
3
(
3
3
makes the present method superior and more advantageous
2006, 89, 16–24.
than existing ones.
20 K. G. Chandra and M. M. Sharma, Catal. Lett., 1993, 19, 309–
317.
2
2
1 E. Dumitriu and V. Hulea, J. Catal., 2003, 218, 249–257.
2 R. Anand, R. Maheswari, K. U. Gore and B. B. Tope, J. Mol.
Catal. A: Chem., 2003, 193, 251–257.
3 Z. K. Zhao, W. L. Wang, W. H. Qiao, G. R. Wang, Z. S. Li and
L. B. Cheng, Microporous Mesoporous Mater., 2006, 93, 164–
Acknowledgements
We sincerely thank to Director, IIP for his kind permission to
publish these results. We are also thankful to analytical sciences
division of the Institute for providing help and support in
analyses of the samples.
2
170.
2
2
2
2
4 G. D. Yadav and N. S. Doshi, Appl. Catal., A, 2002, 236, 129–
147.
5 S. K. Badamali, A. Sakthivel and P. Selvam, Catal. Lett., 2000,
Notes and references
1
2
3
4
5
6
7
8
9
S. E. Dapurkar and P. Selvam, Appl. Catal., A, 2003, 254, 239–
49.
J. H. Huang, L. H. Xing, H. S. Wang, G. Li, S. J. Wu, T. H. Wu
and Q. B. Kan, J. Mol. Catal. A: Chem., 2006, 259, 84–90.
T. Mathew, B. S. Rao and C. S. Gopinath, J. Catal., 2004, 222,
65, 153–157.
2
6 C. H.
Subrahmanyam,
B.
Viswanathan
and
T. K. Varadarajan, J. Mol. Catal. A: Chem., 2005, 226, 155–163.
7 T. Jiang, Y. Ma, J. Cheng, W. Liu, X. Zhou, Q. Zhao and
H. Yin, J. Assoc. Arab Univ. Basic Appl. Sci., 2014, DOI:
1
07–116.
K. Ojha, N. C. Pradhan and A. C. Samanta, Chem. Eng. J.,
005, 112, 109–115.
1
0.1016/j.jaubas.2014.01.003.
8 X. Mo, E. Lotero, C. Lu, Y. Liu and J. G. Goodwin, Catal. Lett.,
008, 123, 1–6.
2
2
3
3
2
2
J. Gui, H. Ban, X. Cong, X. Zhang, Z. Hu and Z. Sun, J. Mol.
Catal. A: Chem., 2008, 225, 27–31.
A. Sakthivel, S. K. Badamali and P. Selvam, Microporous
Mesoporous Mater., 2000, 39, 457.
A. V. Krishnan, K. Ojha and N. C. Pradhan, Org. Process Res.
Dev., 2002, 6, 132.
K. Zhang, H. Zhang, G. Xua, S. Xiang, D. Xu, S. Liu and H. Li,
Appl. Catal., A, 2001, 207, 183.
9 S. P. J. Higson, Analytical Chemistry, Oxford Univ. Press, New
York, 2003, p. 75.
0 A. Takagaki, M. Toda, M. Okamura, J. N. Kondo, S. Hayashi,
K. Domen and M. Hara, Catal. Today, 2006, 116, 157.
1 M. Okamura, A. Takagaki, M. Toda, J. N. Kondo, T. Tatsumi,
K. Domen, M. Hara and S. Hayashi, Chem. Mater., 2006, 18,
3039.
T. Sato, G. Sekiguchi, T. Adschiri and K. Arai, Chem.
Commun., 2001, 1566.
3290 | RSC Adv., 2015, 5, 3286–3290
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