2-Butanol dehydration over highly dispersed molybdenum oxide/MCM-41 catalysts

Article abstract of DOI:10.1002/bkcs.10380

Highly dispersed MoO₃ on SiMCM-41 was applied to the dehydration of 2-butanol. MoO₃/MCM-41 catalysts were prepared using a modified atomic layer deposition method. The structural characteristics of MoO₃ supported on SiMCM-41 were examined by inductively coupled plasma spectrometry, nitrogen adsorption, X-ray photoelectron spectroscopy, and X-ray diffraction. The textural characteristics of SiMCM-41 were retained after loading with MoO₃. Ammonia temperature-programmed desorption and Fourier transformation infrared spectroscopy of adsorbed pyridine showed that Lewis acid sites were formed on the MoO₃/MCM-41 catalysts. Among the MoO₃/MCM-41 catalysts, the MoO₃ (16.4 wt %)/MCM-41 catalyst showed the highest catalytic activity for butene synthesis from 2-butanol dehydration due to the largest number of acid sites.

Full text of DOI:10.1002/bkcs.10380

Article
DOI: 10.1002/bkcs.10380
BULLETIN OF THE
H. Choi et al.
KOREAN CHEMICAL SOCIETY
2
-Butanol Dehydration over Highly Dispersed Molybdenum
Oxide/MCM-41 Catalysts
†
‡
§
†,*
Hyeonhee Choi, Do Heui Kim, Young-Kwon Park, and Jong-Ki Jeon
†Department of Chemical Engineering, Kongju National University, Cheonan 331-717, Korea.
*E-mail: jkjeon@kongju.ac.kr
‡
School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University,
Seoul 151-742, Korea
§
School of Environmental Engineering, University of Seoul, Seoul 130-743, Korea
Received February 5, 2015, Accepted April 7, 2015, Published online July 27, 2015
Highly dispersed MoO on SiMCM-41 was applied to the dehydration of 2-butanol. MoO /MCM-41 catalysts
3
3
were prepared using a modified atomic layer deposition method. The structural characteristics of MoO sup-
3
ported on SiMCM-41 were examined by inductively coupled plasma spectrometry, nitrogen adsorption, X-ray
photoelectron spectroscopy, and X-ray diffraction. The textural characteristics of SiMCM-41 were retained
after loading with MoO . Ammonia temperature-programmed desorption and Fourier transformation infrared
3
spectroscopy of adsorbed pyridine showed that Lewis acid sites were formed on the MoO /MCM-41 catalysts.
3
Among the MoO /MCM-41 catalysts, the MoO (16.4 wt %)/MCM-41 catalyst showed the highest catalytic
3
3
activity for butene synthesis from 2-butanol dehydration due to the largest number of acid sites.
Keywords: Butanol, Dehydration, Butene, Molybdenum oxide, Mesoporous silica
Introduction
addition, WO supported on mesoporous silica could be used
3
to produce butenes through butanol dehydration. This study
12
Many catalytic reactions are carried out over transition metal
focused on highly dispersed MoO on SiMCM-41 prepared
3
1–3
oxides. Mesoporous materials have been used as a support
for metal oxides because of their uniform pore size and large
surface area. Highly dispersed transition metal oxides over
mesoporous material can be synthesized via modified atomic
using a modified ALD method. The Brunauer-Emmett-Teller
(BET) method, inductively coupled plasma spectrometry
(ICP), X-ray photoelectron spectroscopy (XPS), X-ray dif-
fraction (XRD), Fourier transformation infrared spectroscopy
(FTIR) of adsorbed pyridine, and NH3 temperature-
programmed desorption were used to examine the physico-
4–8
layer deposition (ALD) technique. ALD is a type of the sur-
face sol–gel process that makes thin films of metal oxide grow
9
on a planar surface. The modified ALD technique occurs in
chemical characteristics of the supported MoO catalysts.
3
four stages, such as the chemisorption of alkoxide, removal of
the non-chemisorbed alkoxide precursors by rinsing with a9
solvent, hydrolysis of the chemisorbed alkoxide, and drying.
C H isgenerallyproducedbythenaphthacrackingprocess
The catalytic performance in butanol dehydration was evalu-
ated in continuous gas flow with a packed bed reactor.
Experimental
4
8
in the petrochemical industry. Recently, because the naphtha
cracking process has been replaced with a C H cracker, there
SiMCM-41 was synthesized using the method described
2
6
12–15
has been an overall shortage of butenes. In addition, an ethane
cracking process based on the process in the shale gas industry
has recently been established. Because the C H cracking
elsewhere.
Molybdenum oxide was grafted over
6,12
SiMCM-41 via the modified ALD method.
SiMCM-41
powder was suspended in toluene and heated under reflux
for 4 h in bubbling N . MoOCl was also suspended in toluene
2
6
reaction generates a large amount of C H with no C H , there
2
4
4
8
2
4
will be mismatch between the supply and demand in the C H8
andheatedunderrefluxfor8 hunderN atmosphere. Thesolu-
4
2
market. To meet the demand of C H , it is essential to develop
tion containing SiMCM-41 was mixed with a MoOCl solu-
4
8
4
innovative chemical technologies and introduce new raw
materials for the production of butenes. Bio-butanol converted
from cellulose has attracted considerable attention as a biofuel
and has been recognized as an alternative to bio-ethanol.
Recently, many technologies for producing fuel and chemical
products from bio-butanol have been developed by several
tion and heated under reflux for 24 h under a nitrogen
atmosphere. The mixed solution was washed with toluene, fil-
tered, dried at 373 K in an oven, and finally calcined at 773 K
in a furnace. The amount of MoOCl in the precursor solution
4
was varied to obtain a range of molybdenum oxide loadings
(4.4, 10.5, 12.5, and 16.4 wt %) on MCM-41 (MoO3/
10,11
researchers.
MCM-41). A MoO /MCM-41 sample containing more than
3
Previous studies demonstrated that aluminosilicates with an
ordered structure can be used for butanol dehydration. In
16.4 wt % MoO loading could not be obtained even when
3
8
an excess of MoOCl solution was used.
4
Bull. Korean Chem. Soc. 2015, Vol. 36, 1974–1979
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Wiley Online Library
1974

BULLETIN OF THE
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2-Butanol Dehydration over Highly Dispersed Molybdenum Oxide
KOREAN CHEMICAL SOCIETY
The N adsorption isotherms of the catalysts were obtained
2
using a Bel Sorp-mini (Bel Japan Inc., Osaka, Japan) at 77 K.
The surface area was measured using the BET equation. The
pore volume and pore size were obtained according to the
t-plot and the Barrett-Joyner-Halenda (BJH) method, respec-
tively. The crystalline structure of the catalysts was examined
by XRD. ICP (Flame Modula S, Spectro, Kleve, Germany)
was used to determine the amount of molybdenum in the cat-
alyst. XPS (MultiLab ESCA 2000, Thermo Fisher Scientific
Inc., Waltham, MA, USA) was conducted using MgKα radi-
ation (300 W) to determine the oxidation state of molybdenum
oxide on SiMCM-41.
6
5
4
00
00
00
The nature of the acid sites over the MoO /MCM-41 cata-
300
3
12
lysts was investigated using pyridine as a probe molecule.
Fourier transforminfrared (FTIR) spectroscopy of the adsorbed
pyridine (Pyridine-IR) over the catalysts was performed in a
transmission infrared cell. The strength and amount of the acid
sites over the catalysts were measured according to the temper-
ature-programmed desorption of ammonia (ammonia-TPD)
2
00
MCM-41
4
1
1
.4 wt%
0.5 wt%
2.5 wt%
16.4 wt%
8,16
using a BEL-CAT-B (Bel Japan Inc., Osaka, Japan).
The dehydration reaction of 2-butanol was carried out over
100
0
.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/Po)
0
.02 g of MoO /MCM-41 catalysts in a packed bed reactor.
3
After heating the catalyst bed to a certain temperature under
Figure 1. N
2
adsorption-desorption isotherms ofthe MoO
3
/MCM-41
a N flow (400 cc/min), 2-butanol was provided with a flow
catalysts (Filled symbol: adsorption, unfilled symbol: desorption).
2
in a range of 2–16 cc/h using a syringe pump. The N flow
2
was controlled using a mass flow controller. After evaporating
2-butanol through a pre-heater, 2-butanol was injected into the
Table 1. BET surface area, pore volume, and pore size of the MoO3/
reactor in the gas phase. The temperature of the catalyst bed
was adjusted with a tubular electric furnace equipped with a
temperature controller. The gaseous products were analyzed
by gas chromatography (YL 6100 GC, YL Instrument, Seoul,
Korea) equipped with a flame ionization detector and an alu-
minum oxide capillary column.
MCM-41 catalysts.
a
MoO
wt %)
3
loading
S
BET
2
V
P
Pore
size (nm)
3
b
(
(m /g)
(cm /g)
0
4
1
1
1
1059
1025
1001
907
0.97
0.88
0.81
0.78
0.74
3.0
3.0
2.9
2.9
2.8
.4
0.5
2.5
6.4
Results and Discussion
885
a
Figure 1 presents the N adsorption-desorption isotherms of
0
Pore volume measured at P/P = 0.99.
Average diameter of mesopores calculated by BJH method.
2
b
SiMCM-41 and MoO /MCM-41. The N2 adsorption-
3
desorption isotherms show that all the catalysts exhibited
17
hysteresis, a characteristic of mesoporous materials. All
catalysts exhibited typical type IV isotherm curves with a hys-
Figure 2 shows the XRD patterns for the SiMCM-41 and
teresis loop (H1 type) at P/P between 0.3 and 0.4. As the
MoO /MCM-41 catalysts. The small-angle XRD patterns of
3
0
amount of molybdenum oxide loading increased, the shape
of the hysteresis loop was similar despite the reduced amount
the catalysts in Figure 2(a) show one intense peak and two
weak peaks that can be assigned to the (100), (110), and
(200) reflections and are characteristic of a 2-D hexagonal
mesoporous structure. These peaks show that the skeletal
structure of SiMCM-41 is quite uniform. The ordered hexag-
of N adsorbed. This suggests that the shape of pores may be
2
18
almost uniform through the molybdenum oxide deposition
process.
Table 1 lists the BET surface area, pore size, and total pore
volume of the catalysts. The BET surface area and total pore
onal structures of the MoO /MCM-41 catalysts, even at high
3
molybdenum oxide loadings, were confirmed by the low-
angle XRD results. All the samples showed similar character-
istics, suggesting that the mesoporous structure of the
SiMCM-41 can be retained after loading with molybdenum
oxide. More importantly, the XRD peaks arising from the
molybdenum oxides were not detected at higher angles for
any of the catalysts (Figure 2(b)). These results clearly mean
that the molybdenum oxide phases are highly dispersed over
2
3
volume of SiMCM-41 were 1059 m /g and 0.97 cm /g,
respectively. With increased molybdenum oxide loading up
to 16.4 wt %, the BET surface area and the total pore volume
2
3
decreased to 885 m /g and 0.74 cm /g, respectively. The pore
size of SiMCM-41 was 3.0 nm, but it decreased slightly with
increasing molybdenum oxide loading, which can be attribu-
ted to the reduction of the available void volume.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1974–1979
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1975

BULLETIN OF THE
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2-Butanol Dehydration over Highly Dispersed Molybdenum Oxide
KOREAN CHEMICAL SOCIETY
(a)
(b)
1
6.4 wt%
1
6.4 wt%
2.5 wt%
1
2.5 wt%
1
1
0.5 wt%
1
0.5 wt%
4
.4 wt%
4
.4 wt%
MCM-41
50
MCM-41
5
1
2
3
4
10
20
30
40
60
2ꢀ (degree)
2ꢀ (degree)
Figure 2. XRD patterns of the MoO /MCM-41 catalysts (a) low-angle XRD, (b) high-angle XRD.
3
the MCM-41 surface, even with a high molybdenum oxide
loading.
Mo 3d3/2
Mo 3d5/2
Figure 3 shows the molybdenum 3d XP spectra of the cat-
alysts. The Mo 3d spectra had two peaks (3d5/2 and 3d3/2),
which were separated by 3.1 eV. All four samples contained
6
+
Mo (e.g., MoO ) because their main Mo 3d peaks were
3
5/2
19
located at 232.6 eV. As marked in Figure 3, no oxidation
state other than MoO was observed in these samples, suggest-
3
ing that the modified ALD method can produce the same
1
1
6.4 wt%
2.5 wt%
MoO species on MCM-41 within this molybdenum oxide
3
loading range. Moreover, the surface coverage of MoO on
3
MCM-41 increased in proportion to the Mo loading, as evi-
denced by the increase in the area of the Mo 3d peak. Cl 2p
peaks were not detected in any of the samples, indicating com-
plete calcination (not shown).
10.5 wt%
4.4 wt%
Figure 4 shows the effect of the molybdenum oxide loading
over SiMCM-41 on the ammonia-TPD profiles. It was diffi-
cult to find a peak in the ammonia-TPD curve of SiMCM-
2
42
240
238
236
234
232
230
228
A
41, which means that there are few acid sites over the
Figure 3. Mo 3d photoelectron spectra of the molybdenum oxide/
SiMCM-41 surface. The MoO /MCM-41 catalysts exposed
weak acid sites at 170 C, whereas strong acid sites could
MCM-41 catalysts.
3
ꢀ
−
1
not be detected, indicating that only weak acid sites were gen-
erated upon the molybdenum oxide loading. As summarized
in Table 2, the total amount of acid sites was found to increase
with increasing molybdenum oxide loading.
peaks at 1611 and 1454 cm indicate the occurrence of
acid sites with higher strength than the two peaks at 1593
−
1
and 1445 cm . These tendencies are well consistent with
those described in the literature.
1575, and 1454 cm could be indexed to Lewis acid sites.
The peaks at 1593 and 1445 cm were reported to be peaks
that could be generated by hydrogen-bonded pyridine with
20–24
The peaks at 1611,
−
1
Figure 5 shows the FTIR spectra of adsorbed pyridine over
−1
MoO (12.5 wt %)/MCM-41 followed by desorption at a tem-
3
ꢀ
−3
perature range of 25–300 C under 10 torr. At lower tem-
peratures (<100 C), two distinct peaks were detected at
593 and 1445 cm . An increase in desorption temperature
ꢀ
20–24
Si-OH group.
−1
1
The FTIR spectra of pyridine adsorbed over the catalysts at
150 C are shown in Figure 6. The SiMCM-41 catalyst
showed two peaks at 1445 and 1593 cm , which were
assigned to the peaks produced by hydrogen-bonded pyridine
ꢀ
appeared to decrease the intensity of the two peaks at 1593
−
1
−1
and 1445 cm more considerably than that of the three peaks
−1
at 1611, 1575, and 1454 cm . Finally, the peaks at 1611 and
−
1
ꢀ
13
1
454 cm were obvious after desorption at 300 C. The two
(H). This indicates that the SiMCM-41 catalyst has neither
Bull. Korean Chem. Soc. 2015, Vol. 36, 1974–1979
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1976

BULLETIN OF THE
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2-Butanol Dehydration over Highly Dispersed Molybdenum Oxide
KOREAN CHEMICAL SOCIETY
Brønsted acid sites (B) nor Lewis acid sites (L). In addition to
the H sites, Lewis acid sites were generated over the MoO3/
MCM-41 catalysts, which resulted from the formation of
oxide content recorded less than 2.6% 2-butanol conversion
ꢀ
−1
at 200 C and a WHSV of 80 h , the conversion of 2-butanol
increased drastically with increasing molybdenum oxide load-
ing. Eventually, the catalyst with a 16.4 wt % molybdenum
oxide loading showed approximately 26.3% conversion of
MoO -induced acid sites. The relative intensity of the peak
3
−
1
−1
at 1611 cm to that at 1593 cm increased with increasing
MoO loading. This suggests that the amount of Lewis acid
3
sites increases with increasing MoO loading over MCM-
3
41. Both the ammonia-TPD and infrared spectra of the
adsorbed pyridine results mean that weak acid sites, primarily
Lewis acid sites, were generated over the MoO /MCM-41
catalysts.
3
o
3
00
C
The catalytic activity for the dehydration of 2-butanol over
the six catalysts was investigated in a packed bed reactor. First
of all, it was confirmed that 2-butanol barely converted with-
o
2
2
50
00
C
C
ꢀ
out a catalyst at a temperature range of 200 to 250 C, 1 atm
reaction pressure, and a weight hour space velocity
o
1454
−1
(
WHSV, based on flow rate of 2-butanol) of 80 h .
Figure 7 presents the conversion of 2-butanol and selectivity
to butenes. As expected, 2-butanol conversion was very low
o
1
50 C
over pure MoO . While SiMCM-41 with no molybdenum
3
1
575
1
490
1
611 1593
o
1
00 C
1
445
RT
1
800
1700
1600
1500
1400
Wavenumber (cm–1
)
Figure 5. Infrared spectra of adsorbed pyridine over MoO (12.5 wt
3
−
3
%
)/MCM-41 under 10 torr.
1
6.4 wt%
1
2.5 wt%
16.4 wt%
1
0.5 wt%
1
2.5 wt%
4
.4 wt%
MCM-41
1
0.5 wt%
.4 wt%
100
200
300
400
500
4
Temperature (°C)
Figure 4. Ammonia-TPD of MoO /MCM-41 catalysts.
3
MCM-41
Table 2. Acidity of various catalysts by ammonia-TPD.
L
H
L H
L
MoO
0
3
loading (wt %)
Total acidity (mmol/g)
0.2
0.9
0.8
1.0
1.5
4
1
1
1
.4
1800
1700
1600
1500
1400
0.5
2.5
6.4
Wavenumber (cm–1
)
Figure 6. Infrared spectra of adsorbed pyridine over the MoO /
3
ꢀ
−3
MCM-41 catalysts at 150 C under 10 torr.
Bull. Korean Chem. Soc. 2015, Vol. 36, 1974–1979
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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BULLETIN OF THE
Article
2-Butanol Dehydration over Highly Dispersed Molybdenum Oxide
KOREAN CHEMICAL SOCIETY
5
0
3
2
2
1
1
0
5
0
5
0
5
40
3
2
1
0
0
0
0
0
0
50
6
4
2
4
3
2
1
0
0
0
0
0
0
0
trans-2-butene
-butene
cis-2-butene
1
0
5
30
trans-2-butene
-butene
cis-2-butene
1
1
1
2
1
0
0
0
0
5
0
100
200
300
400
500
WHSV(h–1
)
MCM-41
Pure
MoO3
MoO3
MoO3
MoO3
Figure 8. Effect of WHSV on conversion and product distribution
over MoO3 (12.5 wt %)/MCM-41 catalyst (Reaction condition:
50 C, 1 atm, time-on-stream 2 h).
MoO3
4.4 wt% 10.5 wt% 12.5 wt% 16.4 wt%
Catalyst
ꢀ
2
Figure 7. Conversion, selectivity, and yield of 2-butanol dehydration
ꢀ
over various catalysts (Reaction conditions: 200 C, 1 atm, WHSV
−
1
8
0 h , time-on-stream 2 h).
Conclusion
MoO /MCM-41 catalysts were prepared by modified ALD
2-butanol. As shown in Figure 4, the ammonia-TPD con-
3
technique. The textural characteristics of the molybdenum
oxide supported on SiMCM-41 were the same as those on
the bare catalyst. Ammonia-TPD and FTIR spectroscopy of
adsorbed pyridine indicated the formation of weak acid sites,
firmed that the four catalysts had similar acid site
strengths. In addition, the acid sites over the MoO /MCM-
3
41 catalysts consisted of Lewis acid sites and H-bonded weak
acid sites. Therefore, the highest activity of the MoO /MCM-
3
primarily Lewis acid sites, on the MoO /MCM-41 catalysts.
41 catalyst with the 16.4 wt % molybdenum oxide loading can
3
The MoO (16.4 wt %)/MCM-41 catalyst showed the highest
be attributed to the large number of acid sites among the
five catalysts. The selectivity to cis-2-butene was highest over
the MCM-41 and molybdenum oxide-introduced catalysts.
The product distribution in 2-butanol dehydration, however,
was not altered considerably with increasing molybdenum
oxide loading.
3
catalytic activity for 2-butanol dehydration due to the largest
number of acid sites among the MoO /MCM-41 catalysts.
3
Acknowledgments. This researchwassupportedbytheBasic
Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Educa-
tion, Science and Technology (grant number 2010-0023600).
The effect of the space velocity onthe catalytic performance
in 2-butanol dehydration was also investigated over the MoO3
(
12.5 wt %)/MCM-41 catalyst (Figure 8). When the space
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dispersed molybdenum oxide on SiMCM-41 synthesized
using a modified ALD method can serve as a catalyst for
butene synthesis from 2-butanol.
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BULLETIN OF THE
Article
2-Butanol Dehydration over Highly Dispersed Molybdenum Oxide
KOREAN CHEMICAL SOCIETY
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