Cyclodextrin-modified MCM-41 for selective double bond migration

Article abstract of DOI:10.1007/s11164-010-0202-x

Cyclodextrin-modified MCM-41 with relatively high surface area above 1,100 m²/g has been prepared via simple hybridization of cetyltrimethylammonium bromide and cyclodextrin. The modified MCM-41 showed fairly good catalytic performance (high activity and selectivity) in the double bond migration of 2-butene into 1-butene. Springer Science+Business Media B.V. 2010.

Full text of DOI:10.1007/s11164-010-0202-x

Res Chem Intermed (2010) 36:661–667
DOI 10.1007/s11164-010-0202-x
Cyclodextrin-modified MCM-41 for selective double
bond migration
•
Jong-Ki Jeon Young-Kwon Park Jin-Heong Yim
•
Received: 18 February 2010 / Accepted: 27 April 2010 / Published online: 16 September 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Cyclodextrin-modified MCM-41 with relatively high surface area above
1,100 m2/g has been prepared via simple hybridization of cetyltrimethylammonium
bromide and cyclodextrin. The modified MCM-41 showed fairly good catalytic
performance (high activity and selectivity) in the double bond migration of 2-butene
into 1-butene.
Keywords Double bond migration Á MCM-41 Á Cyclodextrin
Introduction
Porous materials with ordered micropores (typically less than 2 nm) have been
widely used as catalysts, adsorbents, and various supporting materials [1–3].
Extensive research has been performed in the syntheses of new porous materials
(MCM-41, MCM-48, SBA-15, MSU-H, etc.) with the goal of extending the pore
diameter to the mesoporous region (typically 2–50 nm) [4–6]. The major application
of porous materials is as catalysts for various fine chemicals syntheses and
petrochemical processes. Recently, our group reported that pure silica MCM-41
exhibits excellent activity and selectivity for the double bond migration of 2-butene to
1-butene, compared with well-known Al2O3-based catalysts and ferrierite zeolite [7].
J.-K. Jeon
Department of Chemical Engineering, Kongju National University, Cheonan 330-717, Korea
Y.-K. Park
School of Environmental Engineering, University of Seoul, Seoul 130-743, Korea
J.-H. Yim (&)
Division of Advanced Materials Engineering, Kongju National University, Cheonan 330-717, Korea
e-mail: jhyim@kongju.ac.kr
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J.-K. Jeon et al.
Control of the pore size and pore size distribution of such mesoporous materials is
possible using different template types along with manipulation of the synthetic
parameters. The potential for the use of cyclodextrin (CD) derivatives as supramo-
lecular templates has previously been established [8, 9]. CD-based porogens have
attractive properties such as a narrow thermal decomposition window and a well-
defined 3-dimensional molecular size. Considering the molecular size of CD and
their linear interaction behavior [10], the size of artificial pores from CD derivatives
is expected to be in a range of 1.5–2.0 nm (micropore region). The typical pore size
of MCM-41 made from an ionic surfactant such as cetyltrimethylammonium bromide
(CTABr) is above 3 nm. In the present work, we make mesoporous materials having
a relatively high surface area, above 1,100 m2/g, using a hybrid template system
(CD ? CTABr), and develop a highly selective and active catalyst for the double
bond migration of 2-butene into 1-butene by using the CD modified MCM-41.
Experiment
Mesoporous catalyst preparation
MCM-41, mesoporous silica, was synthesized following procedures described
elsewhere [11]. After dissolving 12.15 g of cetyltrimethylammonium bromide
(CTABr) in 140 g of distilled water, 50 g of sodium silicate solution (20 wt% SiO2,
Na/Si = 0.5) was added. The reaction mixture was heated to 100 °C in an oven for
24 h, and subsequently cooled to room temperature. After adjusting the pH to 10
with 50% acetic acid solution, the mixture was reacted again at 100 °C for 24 h.
The cycle of cooling, pH adjustment, and heating the mixture was carried out twice
more. The white precipitate was filtered, washed in distilled water, and dried at
100 °C overnight. The product was washed with HCl/EtOH mixture, dried at
100 °C, and finally calcined at 550 °C for 4 h. b-Cyclodextrin (Aldrich) was used as
received. CD modified MCM-41 was simply prepared by mixing adequate amounts
of CD and CTABr (10, 20 wt%, respectively, in this study). CD-modified MCM-41
was synthesized following similar procedures to those used for MCM-41.
Characterization of catalysts
The BET surface area of the catalyst was measured using an ASAP 2010 apparatus
by Micromeritics. The crystallinity of the catalysts was examined with a Rigaku
D/MAX-II XRD device using Cu Ka radiation energy. The acidic property of the
samples was analyzed on the basis of temperature-programmed desorption (TPD) of
chemisorbed ammonia. A 0.02-g sample was placed in a quartz tubular reactor and
pretreated in a helium flow, heated to 500 °C at 10 °C/min, and kept at 500 °C for
2 h. The samples were cooled to 100 °C, and an ammonia pulse was injected. After
the physisorbed ammonia was purged with helium, TPD was carried out.
FT-IR (Perkin-Elmer) was used to analyze the acid sites of the catalysts. This
progressed as follows: 0.013 g of catalyst was taken for analysis and formed into a
disk under high pressure. The IR spectrum was obtained at 350 °C under vacuum,
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Cyclodextrin modified MCM-41
663
and the temperature was lowered to 35 °C. Pyridine was flowed at a constant rate
and allowed to adsorb for 30 min under a vacuum. Under increasing temperature,
the IR spectrum was obtained at 150 °C.
Catalytic activity measurements for double bond migration of 2-butene
A 2-Butene double bond migration reaction was performed using a fixed bed reactor
containing 0.13 g of the catalyst. The reaction temperature, pressure, and the weight
hourly space velocity (WHSV) of 2-butene were 450 °C, 1 atm., and 105 h-1
,
respectively. The products were analyzed using gas chromatography for 2 h from
the beginning of the reaction.
Results and discussion
The maximum diameter of b-CD, which consists of seven glucose units, is about
1.53 and its height is about 0.79 nm. The CDs compound has a truncated cone
shape. It has been reported that cyclodextrins can act as templates for the production
of porous silica materials with pore size closely corresponding with the cyclodextrin
diameters (1.5–2 nm) and bicontinuous ‘‘worm-type’’ pore structures using a
nanocasting concept [12]. On the other hand, MCM-41 having a 3- to 10-nm-sized
pore with a hexagonal crystalline pore structure has been reported. In this study,
CD-modified MCM-41 materials are prepared by mixing 10 and 20 wt% of CD in
CTABr, which is used as a template for MCM-41. Figure 1 shows that the XRD
pattern of CD-modified MCM-41 s was not changed by adding CD compound to
CTABr surfactant up to 20 wt%. The typical characteristic peaks, (100), (110),
Fig. 1 XRD patterns of
CD-modified MCM-41 and
MCM-41
CD-MCM-41 (20%)
CD-MCM-41 (10%)
MCM-41
2
4
6
8
2θ
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J.-K. Jeon et al.
Fig. 2 Hybrid template system for CD-modified MCM-41
(200), and (210), can be observed in the two kinds of CD-modified MCM-41. It is
suggested that the hexagonal structure of MCM-41 is not changed despite the
addition of CD template, which induces a worm-like pore structure (Fig. 2).
However, the amount of nitrogen adsorption of the CD-modified MCM-41
materials increased with increasing CD content in the (CD ? CTABr) template
system (Fig. 3). It is speculated that micropores may be generated from CD at the
pore wall, which consists of hexagonal arrays. Table 1 summarizes BET analysis
data for various CD-modified MCM-41 materials. The pore size appears to be very
similar, falling in a range of 3.3–3.6 nm, but the surface area drastically increased
with increasing CD content in the (CD ? CTABr) template system. In other words,
the role of CD may act as a carving agent of the pore wall of MCM-41 in the CTABr
900
800
700
600
500
400
300
200
100
Fig. 3 BET isotherm of
CD-modified MCM-41 and
MCM-41
MCM-41 adsorption
MCM-41 desorption
MCM-41/CD 10 % adsorption
MCM-41/CD 10 % desorption
MCM-41/CD 20 % adsorption
MCM-41/CD 20 % desorption
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/Po)
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Cyclodextrin modified MCM-41
665
Table 1 Physical properties of
CD-templated MCM-41 samples
with various CD contents
Sample
SBET
(m2/g)
DAVERAGE
˚
(A)
VTotal
(cm3/g)
MCM-41
1132
1212
1301
33.8
33.2
36.0
1.12
1.18
1.34
b-CD MCM-41 (10%)
b-CD MCM-41 (20%)
and CD hybrid template system. When 10 and 20 wt% of CD is added, the surface
area of the MCM-41 materials increased by about 7 and 14.9%, respectively.
Figure 4 shows the FT-IR spectra of pyridine adsorbed on MCM-41 and b-CD-
MCM-41 (10 and 20%) in the region 1400–1,800 cm-1. The samples exhibit bands
at 1,445 and 1,596 cm-1. It was reported that these bands are the only bands found
in pure siliceous materials and can be produced by hydrogen-bonded pyridine (H)
with silanol groups [13–16]. Pyridine-IR results indicate that b-CD-MCM-41 as
¨
well as MCM-41 does not have Bronsted (B) acid sites or Lewis (L) acid sites. As
expected, b-CD-MCM-41 does not show any peak in ammonia temperature-
programmed desorption (NH3-TPD). We previously [17] reported that the H site
might act as an active site for the double bond migration of 2-butene to 1-butene.
The equilibrium mole of 1-butene at these reaction conditions (450 °C and
1 atm) is 26.3%, as calculated using PRO/II with PROVISION [17]. In the case of
the reaction without any catalyst, 2-butene hardly reacts under the reaction
conditions, i.e., 450 °C, 1 atm., and WHSV 105 h-1. The yields of 1-butene as well
as total conversion in 2-butene isomerisation increased when b-CD was added to
MCM-41, as shown in Fig. 5. The yields of 1-butene over b-CD-MCM-41 (10%)
and b-CD-MCM-41 (20%) are 22.0 and 23.2 wt%, respectively. The yields of iso-
butene over b-CD-MCM-41 (10%) and b-CD-MCM-41 (20%) are 0.3 and 0.3 wt%,
respectively. These are higher than that over MCM-41 (19.1 wt%). As shown in
Table 1, the surface area of MCM-41 increased with the addition of b-CD.
1596
1445
CD-MCM-41(20%)
CD-MCM-41(10%)
MCM-41
1800
1700
1600
1500
1400
Wave number (cm-1)
Fig. 4 FT-IR spectra of adsorbed pyridine (150 °C, 10-3 Torr)
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J.-K. Jeon et al.
30
25
20
15
10
5
1-butene
i-butene
0
β-CD-MCM-41
β-CD-MCM-41
MCM-41
(10%)
(20%)
Fig. 5 Yields of 1-butene isomerisation over MCM-41, b-CD-MCM-41 (10%), and b-CD-MCM-41
(20%) (WHSV: 105 h-1, Reaction Temp.: 450 °C)
Consequently, the higher yield of 1-butene on b-CD-MCM-41 than that on MCM-
41 appears to be due to the larger surface area of b-CD-MCM-41, which has weak
acid sites. SiO2 and H-Ferrierite have been reported as a 2-butene isomerization
catalyst, even though the condition was not exactly same (WHSV of this paper is
105 h-1, but that of ref. [17] was 70 h-1). In the case of SiO2 catalyst, 1-butene and
iso-butene yields were 9.2 and 0.0 wt%, respectively. 1-butene and iso-butene
yields represented 21.1 and 21.1 wt%, respectively, when H-Ferrierite was used as
the catalyst.
Conclusion
CD-modified MCM-41 materials having relatively a high surface area were
successfully prepared. The pore structure of the modified MCM-41 was a typical
hexagonal 2-dimensional array. The surface area of CD-templated MCM-41 s
increases with the addition of CD compound in the (CD ? CTABr) template system
due to a carving effect of the CD template on the mesopore wall. These
CD-modified MCM-41 materials show fairly good performance as selective and
active catalysts for the double bond migration of 2-butene into 1-butene.
Acknowledgment This research was supported by Basic Science Research Program through the
National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and
Technology (grant number: 2009-0065498).
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