Zeolite SUZ-4 as selective dehydration catalyst for methanol conversion to dimethyl ether

Article abstract of DOI:10.1246/cl.2004.1048

Zeolite SUZ-4 is found to be a very selective and stable catalyst for producing dimethyl ether in methanol dehydration because the formed dimethyl ether is hardly converted to hydrocarbons, different from ZSM-5 zeolite.

Full text of DOI:10.1246/cl.2004.1048

1048
Chemistry Letters Vol.33, No.8 (2004)
Zeolite SUZ-4 as Selective Dehydration Catalyst for Methanol Conversion to Dimethyl Ether
Shan Jiang,y;yy Young Kyu Hwang,y Sung Hwa Jhung,y Jong-San Chang,y Jin-Soo Hwang,ꢀy
Tianxi Cai,yy and Sang-Eon Parkꢀyyy
yCatalysis Center for Molecular Engineering, Korea Research Institute of Chemical Technology,
P. O. Box 107, Yuseong, Daejeon 305-306, Korea
yyDepartment of Chemistry, School of Chemical Engineering, Dalian University of Technology,
Zhongshan road 158, Dalian 116012, P. R. China
yyyDepartment of Chemistry, Inha University, Incheon 402-751, Korea
(Received May 13, 2004; CL-040549)
Zeolite SUZ-4 is found to be a very selective and stable cat-
alyst for producing dimethyl ether in methanol dehydration be-
cause the formed dimethyl ether is hardly converted to hydrocar-
bons, different from ZSM-5 zeolite.
thesized material was pure K-SUZ-4. Calcined K-SUZ-4 was
ion exchanged with aqueous 1 N NH4NO3 solution under reflux,
washed three times with deionized water, dried at 393 K for 2 h
and then calcined in flowing air at 823 K for 10 h. Through three
times of this exchange procedure, the resulting proton-ex-
changed zeolite with ion-exchange degree of 75% was obtained,
and the sample denotes as H-SUZ-4(75). The XRD pattern of the
ion-exchanged product showed the crystallinity remained con-
stant after the exchange/calcination cycles.
NH3-TPD and pyridine-IR results indicate the presence of
strong acid sites on the surface of H-SUZ-4(75) comparable with
those of H-ZSM-5,10 which is in good agreement with previous
report.9 Moreover, most of the strong acid sites of H-SUZ-4(75)
Dimethyl ether (DME), a natural gas derived product, has
been received much attention recently as an alternative clean
fuel for diesel engines because of its low NOx emission, near-
zero smoke, and less engine noise compared with traditional die-
sel fuels.1 DME is commercially produced in small quantities by
the catalytic dehydration of methanol over solid acid catalysts;2
however, water2 or coke3 blocks active sites for methanol dehy-
dration. The formation of DME from syngas using both the de-
hydration catalyst and the traditional methanol synthesis catalyst
has been proposed as an economic way of DME production,4 but
development of a stable solid acid catalyst for methanol dehy-
dration is still necessary for establishing the process.
are identified as Bronsted-type ones.
¨
Methanol dehydration was carried out with a fixed-bed reac-
tion system at atmospheric pressure described elsewhere.3 The
90
(a)
SUZ-4 zeolite is reported in 1992 and the potassium form
(Si/Al ¼ 6:21) is usually obtained.5 Some exchangeable potas-
sium ions in K-SUZ-4 are preferably located in small cages.6
The structure of SUZ-4 is considered to be a three-dimensional
channel system including main straight ten-membered ring
channels intersected by two arrays of eight-membered ring chan-
nels and small cages linked through double six-membered
rings.7 The minimum and maximum dimensions of the ten-mem-
(b)
80
70
ꢀ
bered ring are 4.6 and 5.2 A, respectively. Recently, it has been
reported that zeolite SUZ-4 is a promising support for lean-NOx
catalysts for high temperature applications.8 It has been pro-
posed that SUZ-4 zeolite has potential as a catalyst and may dis-
play unusual shape-selective properties in comparison with other
zeolites.9 However, despite its potential applications in catalysis,
SUZ-4 has been scarcely studied.7–9 In this communication, we
add another new catalytic property of SUZ-4 on very selective
formation of DME in methanol dehydration.
60
460 480 500 520 540 560 580
Reaction Temperature/K
(a)
100
80
Zeolite SUZ-4 was prepared by a hydrothermal crystalliza-
tion. In a typical synthesis, an aluminum foil (0.4 g, Alfa Aesar)
was dissolved into preformed aqueous KOH solution (KOH
3.29 g, H2O 50.63 g). To the clear solution, 7.93 g of TEAOH
(Aldrich, 20–25 wt %) and 18.23 g of Ludox-As-40 (Aldrich,
SiO2 40 wt %) were added successively while stirring (500
rpm) at 333–353 K. The final mixture with the molar composi-
tion of 16.21 SiO2:Al2O3:7.92 K2O:1.83 TEAOH:506.39 H2O
was transferred to a 100-mL Teflon autoclave and crystallized
for 48 h at 438 K under stirring (500 rpm). The solid product
was washed with water, dried at 393 K for 12 h, and calcined
in air at 823 K for 18 h. The XRD patterns showed that as-syn-
(b)
60
40
460 480 500 520 540 560 580
Reaction Temperature/K
Figure 1. Dehydration of methanol over (a) H-SUZ-4(75) and
(b) H-ZSM-5 catalysts. Reaction conditions: catalyst loading
= 0.1 g, 20–40 mesh; N2 flow rate = 360 mL/h; WHSV =
4 hꢁ1; pCH OH ¼ 0:06 MPa; time on stream = 2 h.
3
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.8 (2004)
1049
products were analyzed with an on-lined gas chromatography
equipped with a GS-Q capillary column and flame ionization
detector. The catalytic performances of these two zeolites are
compared at various reaction temperatures as shown in
Figure 1. The two zeolites exhibit very similar conversions in
the reaction temperature range of 498–573 K (Figure 1a). How-
ever, the DME selectivity over H-SUZ-4(75) is much higher
than that over H-ZSM-5 at high temperature (Figure 1b) even
though H-SUZ-4(75) possesses strong acid sites. High DME se-
lectivity on H-SUZ-4(75) is ascribed to its low activity for con-
version of DME, which is an intermediate in methanol dehydra-
tion to hydrocarbons.11 It is noted that H-SUZ-4(75) is unusually
very inactive for DME conversion reaction even at 723 K, indi-
cating that the subsequent reactions of DME to hydrocarbons
over H-SUZ-4(75) are almost prohibited. In contrast, H-ZSM-
5 exhibits high DME conversion, 93% at 673 K, as illustrated
in Figure 2. It is assumed that the active sites over H-SUZ-
4(75) for methanol dehydration may be different from those
for DME conversion. Moreover, the H-SUZ-4(75) catalyst is
very stable without coke formation for more than 40 h of the re-
action, while H-ZSM-5 is deactivated in the reaction after 8 h
owing to the coke formation.
CH3
AlOCH3
SiOAl
CH3OH...HOzeol.
SiOCH3
(a)
(b)
3000
2900
2800
2700
Wavenumber/cm-1
Figure 3. FTIR spectra of (a) H-SUZ-4(75) and (b) H-ZSM-5
after the adsorption of methanol (100 Torr) at 373 K and subse-
quent evacuation at 523 K for 30 min.
HK-SUZ-4 compared with H-ZSM-5.
In summary, this work demonstrates that H-SUZ-4(75) zeo-
lite exhibits unique catalytic properties in methanol dehydration
to exhibit high DME selectivity and catalyst stability, indicating
that it has potential as a catalyst for dehydration of alcohols.
100
(a)
80
This work was partially supported by the Korea Ministry of
Science and Technology through Research Center for Nanoca-
talysis, one of the National Science Programs for Key Nanotech-
nology and Institutional Research Program.
60
40
References and Notes
20
1
2
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(2004).
(b)
0
500
550
600
650
700
750
3
Reaction Temperauture/K
Figure 2. Conversion of DME to hydrocarbons over (a) H-
ZSM-5 and (b) H-SUZ-4(75). Reaction conditions: catalyst
loading = 0.1 g; GHSV = 3000 mL-DMEꢂg-catalystꢁ1ꢂhꢁ1
4
5
6
Haldor Topsoe, U.S. Patent 4 536 485 (1993).
S. A. I. Barri, U.S. Patent 5 118 483 (1992).
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7730 (2001).
.
The FTIR spectra of zeolites after methanol adsorption at
373 K and further evacuation at 523 K are presented in
Figure 3. It is obvious that upon methanol adsorption H-SUZ-
4(75) zeolite contains skeletal methoxyl groups at 2969 cmꢁ1
and adsorbed methanol species at 2854 cmꢁ1, which are known
to produce DME and water on condensation.11 In the case of H-
ZSM-5 not only skeletal methoxyl groups but also AlOCH3 spe-
cies at 2955 cmꢁ1 are present together with a trace of adsorbed
methanol species. Kubelkova et al. reported the formation of
similar species on HY and H-ZSM-5 with chemisorption of
methanol.12 The surface AlOCH3 species on H-ZSM-5 are as-
signed to methoxy groups formed on nonskeletal Al species,
which can be considered to enhance the C–C bond formation.13
The concentration of AlOCH3 species on surface of H-SUZ-
4(75) is very low compared with the case of H-ZSM-5 so that
this might lead to the less formation of hydrocarbons over
7
8
9
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´
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10 The ZSM-5 zeolite in ammonium form (Si/Al ¼ 15) was
obtained from P. Q Corporation, and was transformed into
the hydrogen form by calcination in flowing air at 823 K
for 10 h.
11 S. R. Blaszkowski and R. A. van Santen, J. Am. Chem. Soc,
118, 5152 (1996).
12 J. Bandiera and C. Naccache, Appl. Catal., 69, 139 (1991).
13 L. Kubelkova, J. Novakova, and K. Nedomova, J. Catal.,
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Published on the web (Advance View) July 19, 2004; DOI 10.1246/cl.2004.1048