Hydrogenation of Cyclohexene in Aqueous Solvent Mixture Over a Sustainable Recyclable Catalyst Comprising Palladium and Monolacunary Silicotungstate Anchored to MCM-41

Article abstract of DOI:10.1002/ejic.201801226

An efficient, highly stable, and ligand-free catalyst consisting of Pd and monolacunary silicotungstate anchored to MCM-41 was synthesized and characterized by various techniques. The synthesized catalyst was used for the hydrogenation reaction of cyclohe

Full text of DOI:10.1002/ejic.201801226

A Journal of
Accepted Article
Title: Hydrogenation of cyclohexene in aqueous solvent mixture over
a Sustainable Recyclable Catalyst Comprising Palladium and
Monolacunary Silicotungstate Anchored to MCM-41
Authors: Anjali Patel, Anish Patel, and Nilesh Narkhede
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201801226
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European Journal of Inorganic Chemistry
10.1002/ejic.201801226
FULL PAPER
Hydrogenation of cyclohexene in aqueous solvent mixture over a
Sustainable Recyclable Catalyst Comprising Palladium and
Monolacunary Silicotungstate Anchored to MCM-41
Anjali Patel* , Anish Patel and Nilesh Narkhede [b]
[
a]
[a]
Abstract: An efficient, highly stable and ligand free catalyst
comprising of Pd and monolacunary silicotungstate anchored to
MCM-41 was synthesized and characterized by various techniques.
The synthesized catalyst was used for hydrogenation reaction of
cyclohexene as model substrate and various reaction parameters
were studied in order to optimize the parameters for maximum
conversion, 95% under mild conditions. The catalyst was regenerated
by simply washing with methanol and reused up to three cycles
without significant loss in the activity. The viability of the catalyst was
evaluated for the different alkenes and ketones and in all cases the
conversion was found to be in the range of 92-99 %. It was also found
that the sustainability arises from SiW11, which binds the palladium
very strongly and thus does not allow its leaching into the reaction
mixture.
R. Neumann has synthesized palladium substituted
polyoxometalate (K PdPW11 as pre-catalyst for
hydrogenation of arene, aldehyde, ketone and vicinal ketone. In
2012, K. M. Parida et al. have reported the synthesis of palladium
based lacunary phosphotungstate supported mesoporous silica
5
O39/C)
1
5
(
50LPdPW11O39/MCM-41) for hydrogenation of p-nitrophenol to p-
1
6
aminophenol at room temperature. In 2013, Kortz and co-
workers have prepared Pd nanoclusters stabilized by
tetrabutylammonim salts of phosphotungstates with the well-
known Keggin [α-PW12
their lacunary derivatives [α-PW11
utilized them for the hydrogenation of 1-Hexene at 30 C under 5
bar continuous H
pressure.17
3
-
62]6- and
56]12- and
O
40] , Wells-Dawsons [P
2
W
18
O
O
o
O
39]7- and [P
2
W
15
2
A literature survey shows that neither of any reports describe
hydrogenation of cyclohexene even though it is one of the
important organic transformations. Cyclohexane has immense
importants for its uses as solvent and as an intermediate for the
synthesis of cyclohexanol and cyclohexanone which are the
chemical commodities to produce adipic acid, caprolactam, nylon
Introduction
Catalytic hydrogenation using heterogeneous transition-metal
catalysts, especially supported palladium, is industrially very
important and widely used over several years.1-3 Supported Pd
catalysts can be synthesized by grafting Pd on solid supports, viz.,
carbon,4-5 zeolites,6-7 mesoporous silica8-9 and metal oxides7,10
which comprises the ligand-free systems owing to economic
synthesis and high stability in air.11-12
6
and nylon 6,6. It also shows that all reported catalysts are based
on lacunary phosphotungstate, no studies were carried out on
lacunary silicotungstate even though it is more stable due to its
anionic nature.18
In the present work, an attempt has been made to design a new
heterogeneous catalyst comprising Pd and monolacunary
silicotungstate (SiW11) anchored to MCM-41. The catalyst, Pd-
SiW11/MCM-41, was synthesized by anchoring SiW11 onto MCM-
However, in all cases, the limited accomplishment of anchored Pd
catalysts is mainly responsible to the in situ formation of Pd (0)
from Pd (II) during the reaction. It is known that the Pd (0) species
are more prone to leaching into the reaction mixture than the Pd
41 support followed by exchange of the counter cations of SiW11
with Pd(II). The Pd-SiW11/MCM-41 was characterized by various
physicochemical techniques and its catalytic activity for
hydrogenation of cyclohexene was evaluated in aqueous phase
by varying different reaction parameters. Recovery and recycling
of the catalyst was also evaluated under optimized conditions.
The selectivity of the catalyst was further evaluated for different
substrates. In order to see the role of the SiW11, Pd was also
supported onto MCM-41 (Pd/MCM-41) and its catalytic activity
was evaluated under optimized conditions.
(
II).13 The leaching and redeposition of Pd (0) species on the
surface result in the agglomeration of Pd (0) species into large Pd
nanoparticles or Pd black, causing a loss of metal dispersion and
surface area.14 Hence, the development of a heterogeneous
catalyst for aqueous phase hydrogenation of organic compound,
free of Pd leaching and agglomeration, is still a challenging task.
The applications of polyoxometalates as (POMs) heterogeneous
catalyst is becoming an important topic of research over the past
decade and most of the studies have been centred on the acid-
catalysed or oxidation transformations. At the same time, the use
of POMs as catalysts in reductive transformations has been less
explored and few reports do exist which include the use of metal
clusters stabilized POMs for the hydrogenation reaction. In 2002,
Results and Discussion
Catalyst characterization
The EDX elemental analysis shows that, in the case of Pd/MCM-
41, the % of Pd found was 6.25 wt%, while for Pd-SiW11/MCM-41
it was 3.26 wt%. In the case of Pd/MCM-41, all the available
protons on the surface of MCM-41 take part in the exchange with
Pd, as a result the % of Pd was high. In the case of Pd-
SiW11/MCM-41, if the protons of SiW11 and of MCM-41 are
expected to be exchanged with Pd, the % of Pd would be
[
a]
Prof. Anjali Patel*and Anish Patel
Polyoxometalates and Catalysis Laboratory, Department of
Chemistry, Faculty of Science, The Maharaja Sayajirao University of
Baroda, Vadodara, 390002, India.
E-mail: anjali.patel-chem@msubaroda.ac.in
Dr. Nilesh Narkhede
[
b]
Bioinorganic Laboratory, Department of Chemistry, Indian Institute
of Technology Bombay, Powai, Mumbai-400 076, India.
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European Journal of Inorganic Chemistry
10.1002/ejic.201801226
FULL PAPER
significantly high. But on the contrary, Pd was found to be only
surface area as well as pore diameter decreases significantly.
This confirms the presence of Pd inside the channels of MCM-41.
The nitrogensorption isotherms of support and catalyst are shown
in figure 3. All the isotherms show type IV behavior and exhibits
H1 hysteresis loop which is a characteristic of mesoporous solids.
3.26 wt%. This indicates the replacement of protons of SiW11 by
Pd in Pd-SiW11/MCM-41. EDX elemental mapping of the catalyst
is shown in Figure 1.
1
9
The adsorption branch of each isotherm displayed a sharp
inflection, which suggests a typical capillary condensation inside
the uniform pores. The position of the inflection point is obviously
related to the diameter of the mesopore, and the sharpness of this
step designates the uniformity of the mesopore size distribution.
In addition, narrow pore size distribution was observed for the
samples indicating long range order over large scales. The
decrease in pore diameter in of Pd-SiW11/MCM-41 is due to the
presence of Pd inside the channels of the support. Further, the
interaction of Pd with SiW11 was confirmed by FT-IR analysis.
Table 1. Surface area and pore diameter of support and the catalyst.
Figure 1. EDX elemental mapping of Pd-SiW11/MCM-41.
2
Sample
Surface area (m /g)
Pore diameter (nm)
MCM-41
659
536
452
4.79
3.96
3.34
SiW11/MCM-41
Pd-SiW11/MCM-41
Figure 2. TGA curve of (a) SiW11/MCM-41 and (b) Pd-SiW11/MCM-41.
The TGA curves of SiW11/MCM-41 and Pd-SiW11/MCM-41 are
shown in Figure 2. The TGA of SiW11/MCM-41 showed weight
loss of 6% up to 180 oC attributed to the removal of adsorbed
water molecules followed by 2% weight loss up to 250 oC was
observed because of loss of water of crystallization. No notable
weight loss was observed after this up to 500 oC. The Pd-
SiW11/MCM-41 showed initial weight loss of 1.6% up to 130 C
Figure 3. Nitrogen adsorption isotherms of MCM-41, SiW11/MCM-41 and Pd-
SiW11/MCM-41.
o
due to the loss of adsorbed water. After this, gradual weight loss
observed up to 300 oC due to the removal of water of
crystallization of SiW11 as well as removal of water via
condensation of silanol groups of the MCM-41. The gradual
The FT-IR spectra of MCM-41, SiW11/MCM-41and Pd-
SiW11/MCM-41 are presented in figure 4. FT-IR of MCM-41
-1
(
Figure 4a) shows a broad band around 1000-1300 cm ,
o
weight loss after 320 C suggests that the catalyst is stable up to
corresponding to the asymmetric stretching of Si-O-Si. The bands
at 460 cm-1 and 808 cm-1 are attributed to the bending vibration of
the Si-O-Si bonds and free silica. The band at 966 cm-1
corresponds to symmetric stretching vibration of Si-OH. The FT-
IR of SiW11/MCM-41 (Figure 4b) shows characteristic bands of
o
3
20 C.
The textural properties such as surface area and pore diameter
are presented in Table 1. The incorporation of SiW11 into the
channels of the support is apparent here, as it leads to 19 %
reduction in surface area as well as 17 % reduction in pore
diameter. This gives first indication of chemical interaction
between SiW11 and MCM-41. Further, after exchange with Pd the
SiW11 at 960 cm-1 (W=O
-1
−1
d
a b
), 900 cm (Si-O ) and 795 cm (W–O –
2
0
W) in good agreement with the reported one. The FT-IR of Pd-
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European Journal of Inorganic Chemistry
10.1002/ejic.201801226
FULL PAPER
SiW11/MCM-41 shows the characteristic bands of SiW11 at 970
exchange with the Pd. Further the absence of characteristic
reflections of SiW11 as well as Pd in the catalyst indicates that Pd-
SiW11 species are highly dispersed inside the hexagonal channels
of MCM-41.
cm- (W=O
1
), 897 cm-1 (Si-O
) and 790 cm−1 (W–O
d
a
b
–W) (Figure
4c). The presence of these bands confirms that lacunary SiW11
remains intact even after exchange with the Pd. Further, the
observed shift in the bands as compared to SiW11/MCM-41
confirms the interaction of Pd with SiW11
.
Figure 6. SEM images of a) MCM-41 and b) Pd-SiW11/MCM-41.
Figure 4. FT-IR spectra of (a) MCM-41, (b) SiW11/MCM-41 and (c) Pd-
SiW11/MCM-41.
Figure 5. XRD patterns of (a) MCM-41 and (b) Pd-SiW11/MCM-41.
Figure 7. TEM images of Pd-SiW11/MCM-41 at (a) 100 nm and (b) 200 nm
resolution.
XRD patterns of MCM-41 and Pd-SiW11/MCM-41 is shown in
figure 5. The XRD pattern of the MCM-41 shows a sharp reflection
around 2θ=2o corresponding to (100) plane indicating well-
ordered hexagonal structure of MCM-41. The comparison of the
XRD pattern of MCM-41 and Pd-SiW11/MCM-41 reveals that the
mesoporous structure of MCM-41 is rather intact even after
Figure 6 shows the SEM images of MCM-41 and Pd-SiW11/MCM-
41. The surface morphology of the catalyst is almost identical to
that of MCM-41. No change in surface morphology of the catalyst
and no separate crystallites of bulk phase of Pd or SiW11 were
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European Journal of Inorganic Chemistry
10.1002/ejic.201801226
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found in the catalyst indicating well dispersion of the species
inside the channels of the support.
the conversion as compared to acetonitrile/water mixture. This
may be due to the increased competitive adsorption of
coordinating solvent on the Pd surface.
TEM images ( Fiagure 7a and 7b) of Pd-SiW11/MCM-41 clearly
shows porous channels spread uniformly through entire surface
as well as presence of Pd(0). Absebsce of separate crystallites of
Pd-SiW11 indicates well dispersion of Pd-SiW11 on the surface of
the catalyst. Furhter the presence of Pd (0) is confirmed by XPS.
100
80
Water (50 mL)
60
Water: Acetonitrile (30:20)
Water: Methanol (30:20)
40
20
0
1
2
3
4
5
6
Time, h
Figure 9. Effect of solvent on hydrogenation of cyclohexene. Reaction
o
conditions: catalyst amount= 100 mg, temperature= 80 C, p(H
2
) = 10 bar.
Figure 8. XPS spectrum of Pd-SiW11/MCM-41
Table 2. Effect of catalyst concentration on cyclohexene conversion.
The XPS of Pd-SiW11/MCM-41 is displayed in Figure 8. A high
Concentration of Pd,
mmol×10
intense peak at 532 eV (3p3/2) with broad peak at 558 eV (3p1/2
)
Catalyst amount
25
-3
% Conversion
are in good agreement with the available reports 21 and confirms
the presence of Pd(0).
7.65
22
73
95
5
0
15.31
30.63
Catalytic activity
100
Reaction conditions: Cyclohexene= 10 mmol, p(H
temperature= 80 C, water: methanol= 30:20 mL.
2
) = 10 bar, time= 2 h,
o
The effect of catalyst concentration on hydrogenation of
cyclohexene was studied by taking 25 mg to 100 mg of the
catalyst containing 7 mg to 31 mg of Pd (Table 2). The results
showed that with increase in the concentration of Pd, the
conversion of cyclohexene was increased. The higher catalyst
concentration would mean a higher number of active sites for
adsorption of the substrate and hence higher conversion. This
suggests that Pd functions as active site for the hydrogenation
reaction. The maximum cyclohexene conversion of 95% was
achieved by using 100 mg of the catalyst.
Scheme 1. Reaction scheme for cyclohexene hydrogenation.
The catalytic activity of Pd-SiW11/MCM-41 was evaluated for
hydrogenation of cyclohexene (Scheme 1) and effect of various
reaction parameters like effect of solvent, catalyst concentration,
reaction temperature and hydrogen pressure were studied in
order to obtain maximum conversion. In all the experiments,
cyclohexane was the only product observed.
The influence of hydrogen pressure was studied for
hydrogenation of cyclohexene as shown in figure 10. The
Effect of solvent on the hydrogenation of cyclohexene was
evaluated and results are presented in Figure 9. While as low as
conversion was increased linearly with increasing H
from 2 to 12 bar and optimum conversion of 95 % was achieved
at H pressure of 10 bar, while it was about 29% at 2 bar,
2
pressure
~15% conversion was observed when water was used as solvent,
2
the use of acetonitrile/water mixture resulted in ~4.5-fold increase
in the conversion of cyclohexene in 2 h of reaction time mainly
due to solubility of cyclohexene in the reaction medium. When,
methanol/water was used as solvent, 95% conversion of
cyclohexene was achieved in 2 h resulting in ~1.4-fold increase in
suggesting the reaction rate depends on the concentration of
hydrogen.
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European Journal of Inorganic Chemistry
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2
equivalent active amount of Pd in form of PdCl in homogeneous
1
00
medium (89 % conversion) as well as Pd/MCM-41 and Pd-
SiW11/MCM-41 in heterogeneous medium (98 % and 95 %
conversion respectively) was obtained. The obtained results show
that we are succeeded in heterogenizing Pd onto SiW11/MCM-41
without any loss in the catalytic activity.
8
0
60
Table 3. Control experiments for hydrogenation of cyclohexene.
Material
% Conversion
TOF, h-1
SiW11/MCM-41[a]
4
-
40
3
5
7
9
11
13
PdCl [
b]
89
158
83
155
2
Pressure, bar
Pd/MCM-41 [a]
98/75/52
95/92/89
Figure 10. Effect of hydrogen pressure on cyclohexene conversion. Reaction
conditions: cyclohexene= 10 mmol, time= 2 h, temperature= 80 oC, water:
methanol= 30: 20 mL.
Pd-SiW11/MCM-41[a]
Reaction conditions: Cyclohexene= 10 mmol, catalyst amount= [a]100 mg,
[
b]
) = 10 bar, time= 2 h, temperature= 80 oC, water: methanol=
3
mg, p(H
2
30:20 mL.
100
Heterogeneity test was carried out by filtering the catalyst from
the reaction mixture at 80 oC after 1 h and the filtrate was
allowed to react up to 2 h. The reaction mixture after 2 h and
the filtrate were analysed by GC. The results of the test showed
80
60
no change in the % conversion for Pd-SiW11/MCM-41
indicating the present catalyst was truly heterogeneous (Figure
12). Also, in Pd-SiW11/MCM-41, the Pd showed no tendency to
agglomerate even after 2 h. i.e. no undesired Pd-black was
formed. In contrast, the heterogeneity test (Figure 12b) showed
that homogeneous catalysis contributes significantly to the
coupling reaction due to leaching of Pd into reaction medium
from Pd/MCM-41. These studies confirm that SiW11 plays an
important role in stabilizing the palladium and do not allow the
leaching of the palladium during the reaction. Also, because of
the higher loading of Pd in Pd/MCM-41, the formation of
palladium black is visible during the reaction. The found
6
0 oC
4
0
0 oC
7
0 oC
8
20
1
2
3
4
5
6
Time, h
Figure 11. Effect of temperature on cyclohexene conversion. Reaction
o
conditions: Cyclohexene= 10 mmol, p(H
methanol= 30:20 mL.
2
) = 10 bar, temperature= 80 C, water:
1
7,
observations are in good agreement with the reported ones.
2
2-23
Figure 11 shows the influence of reaction temperature on the
catalytic hydrogenation of cyclohexene. It was found that with
increase in the reaction temperature, the conversion of
cyclohexene was increased. At 80 C, maximum conversion was
achieved.
1
00
100
80
(a)
(b)
o
8
0
The optimized conditions for maximum conversion of
cyclohexene over Pd-SiW11/MCM-41 are, catalyst amount: 100
60
60
o
mg, reaction time: 2 h, p(H
methanol= 30/20 mL.
2
): 10 bar, temperature: 80 C, water/
Pd-SiW /MCM-41
4
2
0
0
11
40
Pd/MCM-41
Without catalyst filtration
Catalyst filtration
Without catalyst filtration
Catalyst filtration
Control experiments, Heterogeneity and Recycling test
20
0
.5
1.0
1.5
2.0
0.5
1.0
1.5
2.0
The hydrogenation of cyclohexene was carried out using
SiW11/MCM-41, PdCl , Pd /MCM-41 and Pd-SiW11/MCM-41
2
Time, h
Time, h
under optimized conditions. It can be seen from Table 3 that
SiW11/MCM-41 was inactive towards the hydrogenation of
cyclohexene, indicating that the catalytic activity is due to only Pd.
To confirm, the same reaction was carried out by taking an
Figure 12. Heterogeneity test for hydrogenation of cyclohexene over (a) Pd-
SiW11/MCM-41 and (b) Pd/MCM-41. Reaction conditions: catalyst amount=100
o
mg, p(H
2
) = 10 bar, temperature= 80 C, water: methanol= 30:20 mL.
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European Journal of Inorganic Chemistry
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The catalyst was recycled in order to test its activity as well as
stability. The obtained results are presented in Table 3. The
recycled catalyst, Pd-SiW11/MCM-41 did not show any
appreciable change in the activity up to three cycles, indicating
that the catalyst is stable and no leaching of Pd was found from
the catalyst. At the other side, Pd/MCM-41 shows that there is a
significant loss in the activity, suggesting the leaching of Pd during
the reaction. This was further supported by elemental analysis of
the regenerated catalyst by EDX and product mixture by AAS,
suggesting no appreciable loss of Pd content.
catalyst is sustainable during the reaction. Here, the intensity of
regenerated catalyst spectrum is low, may be due to the sticking
of the substrates on the surface, although this might not be
significant in the reutilization of the catalyst.
Characterization of regenerated catalyst
In order to check the constancy, the regenerated catalyst was
characterized for EDX, FT-IR, TEM and XPS.
EDX value of Pd (3.23 wt%) in regenerated Pd-SiW11/MCM-41 is
in good agreement with value of fresh catalyst (3.26 wt% of Pd)
confirming no emission of Pd from Pd-SiW11/MCM-41. This
indicates that SiW11 plays an important role as a stabilizer to keep
the Pd active and also prevent it to leach from the support.
Figure 14. TEM images of Regenerated Pd-SiW11/MCM-41 at (a) 100 nm and
(b) 200 nm resolution.
Figure 13. FT-IR spectra of (a) Fresh Pd-SiW11/MCM-41 and (b) Regenerated
Pd-SiW11/MCM-41.
Figure 15. XPS spectrum of fresh and recycled catalysts.
The FTIR spectra of the fresh and regenerated catalyst are shown
in Figure 13. It can be seen that almost identical spectrum was
obtained without any significant shift in the bands of regenerated
catalyst in comparison with fresh catalyst indicating that catalyst
structure remains intact even after the regeneration. However, the
spectrum intensity was found low in case of regenerated catalyst,
may be due to the sticking of the substrates, although this might
not be significant in the reutilization of the catalyst.24
Table 4. Hydrogenation of different substrates over Pd-SiW11/MCM-41.
%
Substrate
Product
Conversion/
Selectivity
TEM images of regenerated catalyst Pd-SiW11/MCM-41 are
displayed in Figure 14 at various magnifications. Images (14a &
95/99
14b) show the presence of Pd (0) as well as its uniform dispersion
inside the pores of MCM-41. Moreover, obtained images are
almost identical with the fresh catalyst, show the stability and
sustainability of the catalyst during the reaction without aggregate
formation (Pd black).
92/99
85/93
The XPS of fresh and regenerated Pd-SiW11/MCM-41 is
displayed in Figure 15. The obtained spectra are identical with
fresh one confirms that Pd(0) species are stabilized by SiW11 and
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European Journal of Inorganic Chemistry
10.1002/ejic.201801226
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o
at 80 C. The pH was then adjusted to 4.8 by dilute nitric acid. The volume
of the mixture was reduced to half and the resulting solution was filtered to
remove unreacted silicates. The lacunary polyoxometalate anion was
separated by liquid-liquid extraction with acetone. The extraction was
repeated until the acetone extract showed the absence of nitrate ions. The
extracted sodium salt of mono lacunary silicotungstate was dried at room
O
OH
99/99
74/89
O
OH
temperature in air. The resulting material was designated as SiW11
.
Reaction conditions: substrate= 10 mmol, catalyst amount=100 mg, p(H
bar, time= 2 h, temperature= 80 C, water: methanol= 30:20 mL.
2
) = 10
o
A catalyst containing 30% of SiW11 anchored to MCM-41 was synthesized
by impregnation method. 27 MCM-41 (1 g) was impregnated with an
aqueous solution of SiW11 (0.3/30 g/mL of distilled water) and dried at
In order to see the viability of the present catalyst, hydrogenation
of different substrates was carried out over Pd-SiW11/MCM-41
and the results are presented in Table 4. From the Table 4 it is
clear that the catalyst was found to be active for hydrogenation of
both alkenes as well as ketone. However, in the case of
crotonaldehyde where hydrogenation of both C=C as well as C=O
is possible, hydrogenation of only C=O was observed. Here,
Lewis acid sites of SiW11 plays important role in strengthening the
interaction of the catalyst with C=O of crotonaldehyde and
therefore enhance the selectivity of the crotylalcohol.
100 °C for 10 h. The resulting material was treated with 0.1 N HCl, filtered,
washed with double distilled water and dried at 100 °C for 2 h. The
obtained material was designated as SiW11/MCM-41.
Synthesis of Pd exchanged anchored SiW11 was carried out by wet
impregnation of 1 g of SiW11/MCM-41 with 25 mL 0.05 M solution of PdCl
2
for 24 h with stirring. The solution was then filtered, washed with distilled
water in order to remove the excess of Palladium and dried in air at room
temperature. The resulting material was designated as Pd-SiW11/MCM-41.
The same procedure was followed for the synthesis of Pd supported MCM-
41 and the resulting material was designated as Pd/MCM-41.
Conclusions
Elemental analysis was carried out using JSM 5910 LV combined with
INCA instrument for EDX- SEM. TGA was carried out on METTLER
TOLEDO STAR-SW 7.01 instrument. The BET surface area
measurements were performed in a Micromeritics ASAP 2010 volumetric
We have come up with a new heterogeneous catalyst comprising
of Pd (0) nanoparticles and SiW11 anchored to the MCM-41. The
SiW11 species stabilizes the Pd (0) and eliminates the possibility
of formation of Pd black and hence leaching. The BET surface
area measurements suggest that Pd-SiW11 species are present
inside the hexagonal channels of MCM-41. The FT-IR analysis
confirms that SiW11 remains intact even after anchoring on to the
support. The slight shift in the bands confirms the strong
interaction of Pd-SiW11 with the support. XRD pattern confirms
that MCM-41 retains its hexagonal framework structure and well
dispersion of Pd-SiW11 species. The present catalyst was found
to be highly active showing 95% conversion of cyclohexene.
Interestingly, the present catalyst was found to be selective for
C=O hydrogenation in the presence of C=C. The catalyst could
also be regenerated after simple centrifugation and reused up to
three cycles with retention in the activity.
2
static adsorption instrument with N adsorption at 77 K. The pore size
distributions were calculated by BJH adsorption-desorption method. For
FT-IR spectra, samples pressed with dried KBr into discs were recorded
by using a Perkin-Elmer spectrometer. The XRD pattern was obtained by
using PHILIPS PW-1830. The conditions used were: Cu Kα radiation
0
0
(
1.5417 A°), scanning angle from 0 to 60 .The surface morphology of the
support and supported catalyst was studied by scanning electron
microscopy using a JEOL-SEM instrument (model-JSM-5610LV) with
scanning electron at 15 kV. TEM was done on JEOL (JAPAN) TEM
instrument (model-JEM 100CX II) with accelerating voltage 220kV. The
samples were dispersed in ethanol and sonicated for 5-10 minutes. A small
drop of the sample was then taken in a carbon coated copper grid and
dried before viewing. X-ray photoelectron spectroscopy (XPS)
measurements were performed with Auger Electron Spectroscopy (AES)
Module PHI 5000 Versa Prob II.
The catalytic reaction was carried out using Parr reactor instrument having
three major components: The batch type reactor of 100 mL capacity is
made up of SS-316, H
controller. For example, in typical reaction, 10 mmol of cyclohexene with
0 mL solvent (30/20 mL of methanol/water) and 50 mg of catalyst were
charged to the reactor vessel. The reactor was flushed thrice with H gas
2
reservoir and electronic temperature and pressure
Experimental Section
5
The chemicals used were of A.R. grade. Acetonitrile, methanol,
cyclohexene, palladium chloride, sodium tungstate, sodium silicate,
tetraethyl orthosilicate, dichloromethane, n-butylamine and acetone were
purchased from Merck.
2
to remove the air present in the empty part of the vessel. Finally, 10 bar H
2
o
pressure was applied for the reaction. The reaction was set at 80 C with
the stirring rate of 1700 rpm for 4 hours. The continuous decrease in
pressure inside the vessel was utilized for determination of the reaction
progress. After reaction completion, the reaction mixture was cooled at
MCM-41 was synthesized following the previously reported procedure. 25
Surfactant, cetyltrimethylammonium bromide (1 g) was added to the dilute
solution of NaOH (2 M, 3.5 mL NaOH in 480 mL distilled water) with stirring
2
room temperature and then H pressure was released from the vent valve.
The organic layer was extracted using dichloromethane, whereas catalyst
was collected from the junction of the liquid phases and finally recovered
by centrifugation. The organic phases were then dried with anhydrous
magnesium sulfate and analyzed by a gas chromatograph (Shimadzu-
o
at 28 C. Then, 5 mL tetraethyl orthosilicate was added drop wise and the
o
gel was aged for 2 h at 60 C. The resulting material was filtered, washed
o
with distilled water, dried in oven and calcined in air at 550 C for 5 h. The
obtained material was designated as MCM-41.
2014) using a capillary column (RTX-5). The products were recognized by
comparison with the standard samples.
The mono lacunary silicotungstate was synthesized by following the
method reported by Brevard et al. 26 0.22 mol, 7.2 g sodium tungstate and
0.02 mol, 0.56 g sodium silicate were dissolved in 150 mL distilled water
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European Journal of Inorganic Chemistry
10.1002/ejic.201801226
FULL PAPER
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8] N. Mar´ın-Astorga, G. Pecchi, J. L. G. Fierro, P. Reyes, J. Mol. Catal. A:
Chem. 2005, 231, 67-74.
Acknowledgements
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[
[
9] A. Papp, Á. Molnár, Á. Mastalir, Appl. Catal. A: Gen. 2005, 289, 256-266.
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One of the authors Mr. Anish Patel is thankful to Department of
Atomic Energy (DAE) and Board of Research in Nuclear Science
(
BRNS), Project No. 37(2)/14/34/2014-BRNS, Mumbai, for the
[12] S. Pathan, A. Patel, RSC Advances 2012, 116-120.
grant of Junior Research Fellowship. We are also thankful to
Department of Chemistry, The Maharaja Sayajirao University of
Baroda for BET surface area analysis.
[13] M. Choi, D. H. Lee, K. Na, B. W. Yu, R. Ryoo, Angew. Chem. Int. Ed. 2009,
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Keywords: Hydrogenation • Cyclohexene • Palladium •
Monolacunary silicotungstate • MCM-41 • Heterogeneity test
[
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European Journal of Inorganic Chemistry
10.1002/ejic.201801226
FULL PAPER
Entry for the Table of Contents
Layout 1:
FULL PAPER
The new water tolerant catalyst
comprising Pd-SiW11 anchored to
Key Topic*
Pd-SiW11/MCM-41
Author(s), Corresponding Author(s)*
MCM-41 was
synthesized
and
characterized by various techniques
and efficiently used for heterogeneous
hydrogenation of various substrates.
Page No. – Page No.
100
100
75
Title
7
5
2
5
0
5
0
50
Pd/MCM-41
Pd-SiW11/MCM-41
25
Filtration
Without Filtration
Filtration
Without Filtration
0
0
.0 0.5 1.0 1.5 2.0
0.0 0.5 1.0 1.5 2.0
Time, h
Time, h
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