Room temperature efficacious synthesis of diphenylmethane over Fe/Al-MCM-41 catalysts

Article abstract of DOI:10.1016/j.catcom.2010.02.020

Fe/Al-MCM-41 (Si/Al=25, 50, 75 and 100) were synthesized. Their catalytic activity was evaluated towards benzylation of benzene with benzyl chloride in liquid phase. The catalytic activity of Fe/Al-MCM-41(25) was higher than the other catalysts. Diphenylm

Full text of DOI:10.1016/j.catcom.2010.02.020

Catalysis Communications 11 (2010) 876–879
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Room temperature efficacious synthesis of diphenylmethane over
Fe/Al-MCM-41 catalysts
a,
a
b
Muthuraj Esther Leena Preethi ⁎, Thiripuranthagan Sivakumar , Muthiahpillai Palanichami
a
Department of Chemical Engineering, A. C. Tech, Anna University, Chennai, India
Department of Chemistry, Anna University, Chennai, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Fe/Al-MCM-41 (Si/Al=25, 50, 75 and 100) were synthesized. Their catalytic activity was evaluated towards
benzylation of benzene with benzyl chloride in liquid phase. The catalytic activity of Fe/Al-MCM-41(25) was
higher than the other catalysts. Diphenylmethane(DPM) was obtained as the major product with 100%
selectivity and with 100% conversion of benzyl chloride under optimum condition. The effect of temperature
and the feed ratio, on the activity of Fe/Al-MCM-41(25) and selectivity towards DPM was studied and a
possible reaction mechanism was proposed.
Received 25 November 2009
Received in revised form 21 February 2010
Accepted 25 February 2010
Available online 4 March 2010
Keywords:
Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
Diphenylmethane(DPM)
Benzyl chloride(BC)
Al-MCM-41
Benzylation
Mesoporous materials
Iron
1
. Introduction
Homogeneous acid catalysts are normally employed in Friedel–
of interest to design a catalyst for the benzylation of benzene to give
complete conversion of BC with 100% selectivity to the desired DPM
product for industrial applications [17].
Crafts alkylation, but they are not environmentally benign [1]. In
addition catalyst recovery, reuse, waste disposal, corrosion etc are also
the commonly encountered problems. In this context heterogeneous
catalysts are advantageous. For the title reaction earlier studies
indicated poor activity for the solid acid catalyst such as H–Y [2], H-
Up to our knowledge there are no detailed works on the
benzylation of benzene over Fe/Al-MCM-41 catalysts. Aluminium
present in the framework of MCM-41 catalysts activates extra
framework iron thus enhancing the catalyst activity, acidity and
thermal and hydrothermal stability [18–20]. In the present investi-
gation Fe/Al-MCM-41 catalysts with different Si/Al were tested for the
Friedel–Crafts benzylation of benzene. Fe/H–M, Fe/H–Y, Fe/H-ZSM-5
catalysts were also examined for this reaction in order to study the
effect of pore size.
2
ZSM-5 [2,3] and sulphated ZrO [4] for the benzylation of benzene and
other aromatic compounds. Clark et al. [5] reported high activity for
thermally activated clayzic catalyst and the process has been
commercialised. However, clayzic catalyst showed low selectivity
(
∼ 80%) for diphenylmethane(DPM) [5]. Of late iron containing cata-
lysts were rampantly studied for the Friedel–Crafts alkylation due to
their high activity; some of the reported catalysts were FeCl /Mont
K10 [6], sulphated Fe2O –ZrO [4], Fe/MCM-41 [7–9], H–FeMFI
zeolites [3], iron oxide nanoclusters loaded SBA-15 [9], Fe-SBA-15
10], Fe mesoporous silicate catalyst [11,12], Fe-SBA-1 [13] and Fe3+
2. Experimental
3
3
2
Procedures to synthesize Fe/Al-MCM-41(27, 50, 75,100) and the
experimental techniques to characterize the catalyst samples were
described in detail elsewhere [21]. The physico-chemical character-
ization tests of the synthesized catalysts were similar to the previous
report. H–M (Si/Al=12), H–Y (Si/Al=8) and H-ZSM-5 (Si/Al=15),
were procured from Sud Chemicals India Limited. These catalyst
samples were impregnated with iron using a simple wet impregna-
tion procedure as described elsewhere [20].
Liquid phase catalytic benzylation of benzene was carried out in a
magnetically stirred 50 ml glass reactor fitted with a reflux condenser, a
thermometer and a septum to withdraw the product samples. The
temperature of the reaction vessel was maintained using an oil bath. In a
typical run, optimized amounts of benzene and BC (5: 1 mole ratio)
[
loaded SBA-15 [14]. All these iron catalysts required slightly higher
temperature for catalyzing the reaction. Room temperature synthesis
of DPM was reported on SO2
–
/Al-MCM-41 [15] where the conversion
4
of benzylchloride (BC) was 100% but the selectivity towards DPM was
not 100%, and also over AlCl /MCM-41 [16] in which the conversion of
BC was 100% with less than 100% selectivity towards DPM. Hence it is
3
⁎
Corresponding author. Tel.: +91 44 24716816.
E-mail address: epreeti_2003@yahoo.co.in (M.E.L. Preethi).
1566-7367/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2010.02.020

M.E.L. Preethi et al. / Catalysis Communications 11 (2010) 876–879
877
were charged in to the reactor along with 0.1 g catalyst, and the
products were analyzed using 9A model Shimadzu gas chromatograph
equipped with flame ionization detector fitted with OV-101 column
(
2 m length). GC–MS analyses were performed on Shimadzu GC–MS–
QP 5000 with a PE-5 capillary column.
3
. Results and discussion
3
.1. Comparison of catalytic activities of different catalysts studied
Benzylation of benzene with BC over all the synthesized catalysts,
Fe/H–M, Fe/H–Y and Fe/H-ZSM-5 were studied at room temperature
for a duration of 4 h with the mole ratio of 5:1 M (benzene:BC) using
0
1
.1 g catalyst. Equal aliquots of the samples were withdrawn at every
5 min and the results are presented in Fig. 1. Fig. 2 shows the
percentage conversion of BC and the percentage selectivity towards
DPM at the end of the 4 h. The major product was DPM and minor
quantity of polyalkylates like dibenzylbenzene was also present. The
BC conversion and DPM selectivity were higher over Fe/Al-MCM-41
(
25, 50, 75 and 100) catalysts than the microporous Fe/H–Y, Fe/H–M,
Fig. 2. Effect of different catalysts on percentage conversion of BC and selectivity
towards DPM.
and Fe/H-ZSM-5 catalysts. The high selectivity of DPM might be due to
the polar nature of the channel surface owing to the presence of the
activated metal oxides in Fe/Al-MCM-41(25, 50, 75 and 100) catalysts
[
18,19,21]. The main product DPM due to its less polarity should be
temperature increased, the percentage conversion of BC also
increased. Higher conversion at 80 and 100 °C was recorded than at
RT, may be due to rejection of molecular association that aids
dispersed adsorption of BC on the Fe sites. The selectivity to DPM
decreased at higher temperatures, which might be due to Fe and
aluminium ions present over the surface enters the pore as the
temperature is increased, thereby increasing the dispersion and
accessibility of the active sites hence favoring enhanced polyalkyla-
tion with increase in temperature. Hence room temperature is
observed to be the best to obtain 100% selective DPM with 83.4%
conversion of BC.
immediately expelled out of the pore as and when it was formed.
Hence polyalkylation was found to be less. The catalytic activity of the
iron containing mesoporous solid acid catalysts followed the trend,
Fe/Al-MCM-41(25)NFe/Al-MCM-41(50)NFe/Al-MCM-41(75)NFe/Al-
MCM-41(100) which was also the trend of the acidity of the
synthesized catalysts.
The catalytic activity of Fe/H–Y, Fe/H–M and Fe/H-ZSM-5 catalysts
was low as shown in Figs. 1 and 2. This might be due to the small pore
size which enabled least access to the reactant. Pore diameter of
benzene is 5.8 [22] and that of H-ZSM-5 is 5.6 [23] and H–M, and H–Y
in the range 5–7.5 [23]. Due to impregnation procedure their pores
might be partly blocked by the iron oxide particles which are in
agreement with the earlier studies [24,25]. The percentage conversion
of BC was not observed to increase considerably above 210 min and
hence Fe/H–Y, Fe/MOR, and Fe/H-ZSM-5 are not found to be suitable
for this reaction.
3.3. Reaction scheme
A reaction scheme is suggested (Scheme 1) to account for the
formation of the products. Co-ordination of BC on Fe sites might
weaken and ultimately break the CH –Cl bond. The resulting benzyl
2
cation can react with benzene electrophilically to yield the products.
Free radical was not considered favourable, even though this
catalyst has got redox properties. If there is formation of any free
radical intermediate, diphenylethane might also be produced as one
of the major products, since the benzyl radical are highly reactive. But
the product diphenylethane was not observed in this study. Since the
3
.2. Influence of reaction temperature
The liquid phase benzylation of benzene with BC over Fe/Al-MCM-
1(25) was carried out at RT, 80 and 100 °C. The results of percentage
4
conversion and percentage selectivity are shown in Fig. 3. As the
Fig. 3. Effect of temperature on the conversion of BC and selectivity towards DPM over
Fig. 1. Effect of time on stream on percentage conversion of BC over different catalysts.
Fe/Al-MCM-41(25) catalyst.

878
M.E.L. Preethi et al. / Catalysis Communications 11 (2010) 876–879
Table 1
Study of effects of catalyst loading, reactant mole ratio and recyclability at RT on
conversion of BC and product selectivity over Fe/Al-MCM-41(25) catalyst.
Contents
BC
Selectivity of products (%)
conversion
DPM
Others
(%)
Catalyst loading (g)
a
0.1
0.3
0.5
83.4
100.0
100.0
100.0
100.0
98.7
–
a
a
–
1.3
Mole ratio
b
5
5
5
5
5
5
5
5
:0.5
:1
100.0
100.0
100.0
100.0
100.0
83.4
100.0
100.0
100.0
98.6
100.0
100.0
100.0
100.0
–
b
–
b
c
c
:1.5
–
b
:2
1.4
–
:0.5
c
:1
–
:1.5
62.7
56.2
–
c
:2
–
Recyclability
a,c
Scheme 1. Mechanism of benzylation of benzene with BC.
Fresh
83.4
83.1
83.0
100.0
100.0
100.0
–
–
–
a,d
First cycle
Second cycle
a,e
metal oxides are of nanodimensions, those should have high surface
free energy sufficient enough to activate BC by Lewis acid base
interaction without subsequent change in its valency. Activation of
benzene was required to be present for benzylation based on
alkylation of benzene in ZSM-5 [7]. But this supporting evidence
seems to be contradicting as the formed DPM would produce large
sterric congestion within its pores. Hence we are much reluctant to
apply activation of benzene by the metal oxide. If the said activation
really exists over metal oxide, there might be tremendous ring
deactivation because of high charge transfer between the ring and the
Lewis acid sites.
Reaction conditions: temperature = RT, time=4 h.
a
Mole ratio=5:1(B:BC).
Catalyst weight=0.3 g.
Catalyst weight=0.1 g.
Catalyst weight=0. 99 g.
b
c
d
e
Catalyst weight=0.98 g.
highly active Fe/Al-MCM-41 was investigated for various mole ratios of
the reactant.
The results given in Table 1 showed that at lower concentration of
BC 5:0.5(B:BCl), the percentage conversion of BC was 100% with 100%
selectivity towards the desired product. When the mole ratio is varied
by increasing the concentration of BC, the percentage conversion of BC
decreased significantly with 100% selectivity towards DPM which
might be due to the less availability of active sites at lower catalyst
weight. Hence B:BC mole ratio of 5:1.5 with 0.3 g was taken as the
optimum one since higher concentration of BC and its 100%
conversion should give greater quantity of 100% selective DPM.
The released HCl in this electrophilic alkylation can greatly activate
3+
Fe
should have undergone hydrolysis producing Fe(OH)
Fe(OH) [26] species. Fe(OH) decomposes to form Fe
forms FeO . The later species remains as charge compensating
2 3
O for the subsequent activation of BC. During ion exchange Fe
2
+
+
2
, Fe(OH)
2
and
+
3
3
2 3
O and Fe
+
+
(
OH)
2
ion for the framework ‘−'ve charge of Al species. It can act as Lewis
acid site to catalyse benzylation. It could have reacted with BC and
yielded benzyl cation which in turn would have reacted with benzene
to produce diphenylmethane DPM. Hence the ionic mechanism is
more probable for this reaction. Enhanced activation by HCl is also
evident by the enhanced conversion at the end of 4 h, in comparison
to conversion at the end 2 h (Fig. 1) over each catalyst.
3.6. Recycling of the catalyst
Fe/Al-MCM-41(25) used in the benzylation of benzene was
recycled two times in order to check its activity, stability and
reusability. The results are shown in the Table 1. After completion of
the reaction on fresh catalyst, the catalyst was filtered from the
reaction mixture using a Whatmann filter paper, washed with acetone
and air dried. It was incinerated to obtain the catalyst at 823 K for 4 h
in the presence of air. The weight of the catalyst measured after
calcination in the first and second cycle was 0.99 and 0.98 g
respectively. The activity of the Fe/Al-MCM-41(25) decreases pro-
gressively but slightly with increase in the number of cycles. The
selectivity towards the desired product was 100%.
3
.4. Influence of catalyst concentration
Table 1 displays the conversion of BC and product distribution after
h of the reaction time, as a function different catalysts weights over
4
Fe/Al-MCM-41(25). The BC conversion and the selectivity of DPM was
00% when the catalyst used constituted the weight of 0.3 and 0.5 g.
1
The percentage yield of DPM varies linearly with the concentration of
the catalyst. The selectivity of DPM reduced at 0.5 g of catalyst, which
might be due to the exposure of the reactant and product to larger
number of active sites than required which facilitates polyalkylation.
3
.5. Influence of benzene to BC mole ratio
4
. Conclusions
Table 1 exhibits the effect of benzene/BC mole ratio on the catalytic
activity of Fe/Al-MCM-41(25) at room temperature using a catalyst
weight of 0.3 g. The ratios were changed by keeping the amount of
benzene which is taken comparatively in excess to be constant. The data
at RT showed that at higher catalyst weight (0.3 g), the percentage
conversion of BC remained to be 100% regardless of the change in B:BC
mole ratio until 5:1.5(B:BC), but at 5:2(B:BCl), the selectivity toward
DPM was reduced. In order to get better understanding, 0.1 g of the
It is proved that Fe/Al-MCM-41(25) is highly efficacious towards
the benzylation of benzene. At room temperature with B:BCl(5:1.5),
over 0.3 g of Fe/Al-MCM-41(25) catalyst we can obtain a high yield of
DPM with 100 % selectivity and 100% conversion of BC. Free radical
mechanism was not suitable for this reaction since we didn't obtain
diphenylethane as one of the products. The highly active Fe/Al-MCM-
41 catalysts can be applied to many other acid catalyzed reactions.

M.E.L. Preethi et al. / Catalysis Communications 11 (2010) 876–879
879
[
14] C. Anand, P. Srinivasu, S. Alam, V.V. Balasubramanian, D.P. Sawant, M.
Palanichamy, V. Murugesan, A. Vinu, Micropor. Mesopor. Mater. 111 (2008)
References
7
2–79.
[
[
[
[
1] G.A. Olah, Friedel–Crafts Chemistry, Wiley, New York, 1973.
[
[
[
[
[
15] Y. Li, Y. Chen, L. Li, J. Gu, W. Zhao, L. Li, J. Shi. Appl. Catal. A. 366 (2009) 57–58.
16] M. Selvaraj, T.G. Lee, J. Mol, Catal A. 243 (2006) 176–182.
17] X. Hu, G.K. Chuah, S. Jaenicke, Appl. Catal. A. 217 (2001) 1–9.
18] T.W. Bastock, J.H. Clark, Speciality Chemicals, Elsevier, London, 1991.
19] S.H. Choi, B.R. Wood, A.T. Bell, M.T. Janicke, K.C. Ott, J. Phys. Chem. B. 108 (2004)
2] B. Cog, V. Gourves, F. Figueras, Appl. Catal. A. 100 (1993) 69–75.
3] V.R. Choudhary, S.K. Jana, B.P. Kiran, Catal. Lett. 59 (1999) 217–219.
4] S.N. Koyande, R.G. Jaiwal, R.V. Jayaram, Ind. Eng. Chem. Res 3 (37) (1998)
908–913.
[
5] J.H. Clark, A.P. Kybett, D.J. Macquarrie, S.J. Barlow, P.J. Landon, J. Chem. Soc., Chem.
Commun. (1989) 1353–1354.
6] S.G. Pai, A.R. Bajpai, A.D. Deshpande, S.D. Samant, Synth. Commun. 27 (1997)
8970–8975.
[
[
20] B. Wichterlova, Z. Sobalik, J. Dedecek, Appl. Catal. B. 41 (2003) 97–114.
21] M. Esther Leena Preethi, S. Revathi, T. Sivakumar, D. Manikandan, D. Divakar, A.
Valentinerupa, M. Palanichamy, Catal. Lett. 120 (2008) 56–64.
22] L. Capek, V. Kreibich, J. Dedecek, T. Grygar, B. Wichterlova, Z. Sobalık, J.A. Martens,
R. Brosius, V. Tokarova, Micropor. Mesopor. Mater. 80 (2005) 279–289.
23] C.W. Lee, W.J. Lee, Y.K. Park, S.E. Park, Catal. Today. 61 (2000) 137–141.
24] J.F. Denayer, W. Souverijns, P.A. Jacobs, J.A. Martens, G.V. Baron, J. Phys. Chem. B.
[
2267–2273.
[
[
[
7] V.R. Choudhary, S.K. Jana, J. Mol. Catal. A. 180 (2002) 267–276.
8] J. Cao, N. He, C. Li, J. Dong, Q.Xu. Stud Surf, Sci Catal 117 (1998) 461–467.
9] N. He, S. Bao, Q. Xu, Appl Catal A. 169 (1998) 29–36.
[
[
[
[
[
[
[
10] Y. Sun, S. Walspurger, J. Tessonnier, B. Louis, J. Sommer, Appl. Catal. A. 300 (2006)
1–7.
1
02 (1998) 4588–4597.
25] M.M. Mohamed, N.S. Gomaa, M.E. Moselhy, N.A. Eissa, J Colloid Interface Sci 259
2003) 331–337.
11] A. Vinu, D.P. Sawant, K. Ariga, K.Z. Hossain, S.B. Halligudi, M. Hartmann, M.
Nomura, Chem. Mater. 21 (17) (2005) 5339–5345.
12] K. Bachari, J.M.M. Millet, B. Benaichouba, O. Cherifi, F. Figueras, J. Catal. 221 (2004)
5–61.
13] K. Bachari, J.M.M. Millet, P. Bonville, O. Cherifi, F. Figueras, J. Catal. 249 (2007)
2–58.
[
[
(
26] S.V. Priya, J.H. Mabel, S. Gopalakrishnan, M. Palanichamy, V. Murugesan, J. Mol.
5
Catal. A. 290 (2008) 60–66.
5