Highly selective formation of propylene from methanol over high-silica EU-1 zeolite catalyst

Article abstract of DOI:10.1016/j.catcom.2012.08.011

High-silica EU-1 zeolite (SiO₂/Al₂O₃ = ~ 400) was tested in methanol to propylene (MTP) reaction and was found to be a very efficient catalyst. In comparison with the other three high-silica zeolites, i.e. ZSM-48, ZSM-5, and beta zeolites, a higher propylene selectivity (52%) and remarkably high propylene/ethylene (P/E) ratio (15) were obtained under the operating conditions of T = 450°C, P = 0.1 MPa, and WHSV = 1.5 h^{- 1}. Besides, a substantially low amount of C_{5 +} hydrocarbons, especially aromatics is another prominent feature of the product distribution over high-silica EU-1 catalyst. Crown Copyright

Full text of DOI:10.1016/j.catcom.2012.08.011

Catalysis Communications 28 (2012) 95–99
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Highly selective formation of propylene from methanol over high-silica EU-1
zeolite catalyst
⁎
⁎
Si Hu, Yanjun Gong , Qinghu Xu, Xiaoling Liu, Qing Zhang, Lanlan Zhang, Tao Dou
State Key Laboratory of Heavy Oil Processing, The Key Laboratory of Catalysis of CNPC, China University of Petroleum, Changping, Beijing 102249, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 April 2012
Received in revised form 11 July 2012
Accepted 13 August 2012
Available online 18 August 2012
High-silica EU-1 zeolite (SiO2/Al2O3=~400) was tested in methanol to propylene (MTP) reaction and was found
to be a very efficient catalyst. In comparison with the other three high-silica zeolites, i.e. ZSM-48, ZSM-5, and beta
zeolites, a higher propylene selectivity (52%) and remarkably high propylene/ethylene (P/E) ratio (15) were
obtained under the operating conditions of T=450 °C, P=0.1 MPa, and WHSV=1.5 h−1. Besides, a substantial-
ly low amount of C5+ hydrocarbons, especially aromatics is another prominent feature of the product distribu-
tion over high-silica EU-1 catalyst.
Keywords:
Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
Methanol to propylene
Propylene selectivity
Propylene/ethylene ratio
EU-1 zeolite
1. Introduction
a super high P/E ratio could be obtained over beta (*BEA) zeolite
with 3-dimensional (D) 12-MR large-pore channels [8,13,14]. They
With the advantage of cheap feedstock and high propylene yield,
methanol to propylene (MTP) process is promised to be an alterna-
tive technique for propylene production in the post-oil society, and
thus has attracted a lot of interest from both scientific and industrial
viewpoints [1–7]. The MTP process was originally developed by
Lurgi by optimizing propylene yield in methanol to olefin process.
At least 35% of one-pass propylene selectivity was achieved at normal
or nearly normal pressure and reaction temperature of 350 to 500 °C
by using fixed bed reactor and ZSM-5 (MFI) zeolite catalyst [1,2]. Over
the past decade, much more efforts have been devoted for promoting
the performance of catalyst. Particularly, the improvement of propyl-
ene selectivity and propylene/ethylene (P/E) ratio has been regarded
as the challenge and emphasis of current research [1–4,6–10].
In the past years, various zeolite catalysts have been investigated
in the methanol conversion reaction and showed that the product selec-
tivity depended largely on the topological structure of zeolite
[7,8,10–16]. Thus far, zeolite with 10-member ring (MR) channels
(high-silica ZSM-5 zeolites, typically) was considered to be the suitable
catalyst for propylene production from methanol [1–6,10,12,16–23].
However, the further improvement of propylene selectivity over
ZSM-5 catalyst remains a challenge due to the inherent topology feature
of MFI zeolite. This promotes us to seek for an alternative catalyst with
different topologies.
put forward a reasonable explanation that the wide channel intersec-
tion of beta zeolite provided enough space to accommodate the bulky
intermediate species, such as penta- and hexamethylbenzene, which
were involved in an aromatics based hydrocarbon pool type mecha-
nism leading predominantly to propylene and higher alkenes, while
extremely small amounts of ethylene were observed [8,13,14]. How-
ever, the propylene selectivity over beta zeolite was not enhanced be-
cause the large pores facilitated the formation and diffusion of big
molecules, thereby more C4+ hydrocarbons were yielded. This pro-
vides guidelines for the development of a new highly efficient catalyst
for MTP.
EU-1 (EUO) zeolite is one of the most interesting materials, which
possesses one-dimensional (1-D) channel system with 10-MR open-
ings running along the direction connected to 12-MR side pockets
in the (001) direction [24]. Owing to this intriguing structure that be-
tween 10-MR medium-pore and 12-MR large-pore structure, EU-1
exhibits unique catalytic performance in the fields of catalysis reac-
tion, such as isomerization of C8 aromatics, cracking of naphtha, and
methanol to gasoline [25–29]. It is noteworthy that the dimension
of 12-MR side pockets in EU-1 zeolite (6.8×5.8 Å) is similar to that
of beta (6.6×6.7 Å, 5.6×5.6 Å), but its 10-MR channel is more con-
fined. Thereupon, we envisage that an enhanced propylene selectivity
and P/E ratio would be obtained over EU-1 zeolite in MTP reaction. In
the present study, a high-silica EU-1 zeolite with SiO2/Al2O3 ratio of
approximately 400 was used in the MTP reaction for the first time.
Further, its catalytic performance, especially in terms of propylene se-
lectivity and P/E ratio, was compared with those of ZSM-48 (*MRE),
ZSM-5, and beta zeolite.
Bjørgen et al. have carried a lot of works on the theoretical study
of methanol conversion over various zeolite catalysts and found that
⁎ Corresponding authors. Tel.: +86 10 89733066; fax: +86 10 89734979.
E-mail addresses: gongyj@cup.edu.cn (Y. Gong), doutao@cup.edu.cn (T. Dou).
1566-7367/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.08.011

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S. Hu et al. / Catalysis Communications 28 (2012) 95–99
2. Experimental
2.1. Catalyst preparation
EU-1 and ZSM-48 zeolites were synthesized successfully in the
presence of hexamethonium bromide (HMBr) using the approach
reported in our previous work [30]. ZSM-5 and beta zeolites were
synthesized according to the methods reported previously [6,31]. To
obtain the H-form, the as-synthesized materials were calcined in air
at 550 °C for 5 h to remove the template and then ion-exchanged
twice in 1 mol/L NH4Cl solution at 90 °C for 2 h. Then, the zeolites
were calcined at 550 °C for 3 h again. Before conducting catalytic
tests, the protonated zeolites were tableted, crushed, and sieved to
20–40 mesh.
2.2. Catalyst characterization
XRD patterns of the samples were recorded on a Bruker D8 Ad-
vance X-ray diffractometer (40 kV, 40 mA) using Cu Kα radiation.
The morphologies of the samples were observed by scanning electron
microscopy (SEM, FEI Quanta 200F). The BET surface areas of the cat-
alysts were determined by measuring N2 adsorption isotherms on a
Micromeritics ASAP 2020 instrument. Before measurements, the sam-
ples were degassed at 300 °C under vacuum for 5 h.
The element compositions of the prepared catalysts were mea-
sured using a Rigaku ZSX-100 X-ray fluorescence (XRF) analyzer.
Temperature-programmed desorption of ammonia (NH3-TPD) was
carried out to evaluate the acidity of the samples. Prior to the mea-
surements, about 200 mg of sample (particle size 40–60 mesh) was
degassed at 600 °C for 2 h. After cooling to 100 °C, the sample was
saturated in NH3 stream for 30 min, followed by purging with nitro-
gen for 1 h to remove co-adsorbed NH3. The remaining strongly
adsorbed NH3 was then desorbed by heating the sample to 600 °C
at a constant rate of 10 °C/min, and the TPD signal was monitored
by thermal conductivity detector (TCD) simultaneously.
Thermo gravimetric analysis (TGA) was performed on a Netzsch
STA 409 PC analyzer to estimate the amount of coke deposit after re-
action. In a typical measurement, approximately 10 mg of catalyst
was heated to 150 °C in N2 flow at 30 ml/min firstly until no weight
loss occurred. Afterward, the TG curve was recorded as the catalyst
was heated from 20 °C to 800 °C at a constant rate of 5 °C/min
under flowing air (60 ml/min). The sample weight loss occurring at
300–700 °C was taken as the total coke content.
Fig. 1. XRD patterns of (a) EU-1, (b) ZSM-48, (c) ZSM-5, and (d) beta zeolite.
[28], ZSM-5 [6], and beta [31] zeolites are observed, indicating the
high crystallinity and pure phases of the obtained zeolites. To avoid
confounding factors, samples with similar particle size were employed
in this study, and their crystal morphologies are depicted in Fig. 2. As
shown, EU-1 zeolite is typical petal-like crystal, with the petal length
of 0.5–0.8 μm, while ZSM-48 zeolite appears as conglobulations with
the size of 0.4–0.7 μm. ZSM-5 zeolite shows oblate cylindrical shape of
about 0.4–0.8 μm in diameter and beta zeolite displays four-side
saucer-shaped cube with the size of 0.5–0.8 μm. Thus, all of the samples
employed in this study are observed to have the similar particle size in
submicron scale.
Table 1 lists the structural features and physical–chemical proper-
ties of EU-1, ZSM-48, ZSM-5, and beta zeolites. The four samples had
BET surface areas of 347, 242, 352, and 558 m2/g, respectively, which
were similar to those reported previously [6,28,31]. Fig. 3 shows the
NH3-TPD profiles of all the zeolite catalysts. Two desorption peaks
could be observed in the temperature ranges of 220–250 °C and
390–420 °C, which were ascribed to NH3 desorption from weak acid
sites and strong acid sites [3,12,21], respectively. From Fig. 3, it
could be found that the acid site densities of the four zeolite catalyst
employed here are reasonably similar.
2.3. Catalytic tests
3.2. Catalytic performance
The MTP reaction was conducted in a fixed-bed reactor under at-
mospheric pressure at 450 °C. For each test, 1 g catalyst was loaded
to a quartz tube reactor with an inner diameter of 8 mm. Methanol
was fed by passing N2 (PMeOH =20 kPa) through a saturation evapo-
rator at a weight hourly space velocity (WHSV) of 1.5 h−1. The prod-
ucts were analyzed online using a gas chromatograph (Agilent GC
7890) equipped with a flame ionization detector (FID) and an
HP-PLOT Q capillary column (30 m, 0.53 mm id, stationary phase
thickness 40 μm). The column temperature was maintained at 50 °C
for 3 min and then increased to 250 °C at a ramping rate of 10 °C/min
(hold time=15 min at 250 °C). Dimethyl ether (DME) was considered
to be unconverted reactant and lumped together with methanol in the
calculation of conversion and selectivity.
Fig. 4 shows the product distribution measured after 0.1 h on
stream when the catalysts yielded nearly full conversion and were
presumably free from coke. As seen, a much prominently larger
amount of propylene (ca. 52%) and a high P/E ratio (ca. 15) were ob-
served on EU-1 catalyst. While for the two 10-MR zeolitic materials,
i.e. ZSM-48 and ZSM-5, 44% and 40% of propylene selectivities as
well as 9 and 5 of P/E ratio were obtained, respectively. Consistent
with the result reported previously [14,32], beta zeolite (12-MR
pore structure) showed a lower propylene selectivity of 36%, but a
much higher P/E ratio of 17. Thus, it appears likely that a high selectivity
to propylene can be achieved on 10-MR zeolites and a high P/E ratio can
be achieved on 12-MR zeolites.
Moreover, it is worth noting that compared with the other three
zeolite catalysts, EU-1 displayed a fairly low C5+ hydrocarbon selec-
tivity of ~13%, including ~1% selectivity for aromatics, which are
much lower than the results reported by Teketel et al. [28,29] by rea-
son of the higher SiO2/Al2O3 ratio of EU-1 zeolite employed in the
present work. Thus, a considerably high selectivity toward C2–C4
alkenes (ca. 82% at full methanol conversion) was obtained on EU-1
3. Results and discussion
3.1. Catalyst characterization
Fig. 1 shows the XRD patterns of prepared zeolites used in this
study. Typical diffraction lines corresponding to EU-1[30], ZSM-48

S. Hu et al. / Catalysis Communications 28 (2012) 95–99
97
Fig. 2. SEM images of (a) EU-1, (b) ZSM-48, (c) ZSM-5, and (d) beta zeolite.
zeolite, which was much higher than those on ZSM-48 (71%), ZSM-5
(69%), and beta (68%) zeolite. To the best of our knowledge, such a
high selectivity toward lower olefin, together with high propylene
selectivity and high P/E ratio, is seldom observed over zeolite with a
single 10-MR or 12-MR channel system.
Besides, the product selectivities as a function of methanol conver-
sion over the four zeolite catalysts were investigated, and it could be
found that EU-1 exhibited a considerably higher selectivity to propyl-
ene, regardless of the methanol conversion, from ~40% to ~100%
(Table S1 in the Supplementary information). The excellent catalytic
performance of high-silica EU-1 in MTP reaction could be attributed to
its unique topological structure. As summarized in Table 1, ZSM-48,
ZSM-5, and EU-1 have 10-MR pore openings but different channel sys-
tems. ZSM-48 has only 1-D straight channels, while ZSM-5 possesses a
3-D intersecting pore system. EU-1 consists of unidimensional 10-MR
channels, along which 12-MR side pockets (6.8×5.8×8.1 Å) are alter-
nately disposed. Thus, in contrast to ZSM-48 and ZSM-5 zeolite, the
higher propylene selectivity and higher P/E ratio on EU-1 might be as-
cribed to the presence of 12-MR side pockets. Besides, very similar to
the case of beta zeolite with 12-MR large pores, higher butylenes selec-
tivity and higher P/E ratio could be observed on EU-1 zeolite. Hence, we
speculated that the 12-MR side pockets have a very considerable influ-
ence on the product distribution of EU-1 zeolite, although a definitive
explanation for this observation cannot be formulated on the basis of
the current data.
Teketel and his coworkers have analyzed the hydrocarbons
trapped in the zeolite channels during the reaction and revealed
that compared to ZSM-48 and ZSM-5 zeolites, the distribution of
retained species within EU-1 zeolite was substantially shifted toward
Table 1
Structural features and physical–chemical properties of zeolites under study.
Channel typeb
Channel
SBET
Coke depositc
a
Material SiO2/Al2O3
ratio
sizeb (Å) (m2/g) (mg-coke/
g-catalyst)
EU-1
403
1-D 10-MR with
side pockets
1-D 10-MR without 5.3×5.6
side pockets
4.1×5.4
347
242
17
40
12
15
ZSM-48 410
ZSM-5
beta
386
400
3-D 10-MR
5.1×5.5, 352
5.3×5.6
6.6×6.7, 558
5.6×5.6
3-D 12-MR
a
Determined by XRF.
b
Structural data obtained from the International Zeolite Association, see: http://
www.iza-structure.org/databases/.
c
Fig. 3. NH3-TPD profiles of (a) EU-1, (b) ZSM-48, (c) ZSM-5, and (d) beta zeolite.
Calculated by TG analysis after 10 h of operation.

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S. Hu et al. / Catalysis Communications 28 (2012) 95–99
surface. In contrast, EU-1 retained a methanol conversion of approxi-
mately 98% after 20 h on stream, with the highest propylene selectivity
(Fig. S1 in the Supplementary information). As comparison with the
results reported previously over low-silica EU-1 under the similar reac-
tion conditions [28,29], the methanol conversion capacity of high-silica
EU-1 was greatly increased. This may be attributed to its low density of
acid sites, which made a good contribution to its high durability for coke
formation (17 mg-coke/g-catalyst after 10 h on stream). High-silica
beta catalyst also showed a good resistance to coke deposit, and
15 mg-coke/g-catalyst was detected after 10 h of operation, but the pro-
pylene selectivity was relatively low. As widely reported [1–6,19–23],
ZSM-5 catalyst displayed the most excellent stability and the slowest
rate of deactivation. After 10 h on stream, only 12 mg-coke/g-catalyst
was detected in the present study, and the methanol conversions
maintained at around 99% even after 100 h of operation. Clearly, com-
pared with the other three catalysts, EU-1 gave the highest propylene se-
lectivity and extremely high P/E ratio throughout the entire MTP process.
Although the catalytic lifetime was substantially shorter as compared
with ZSM-5, EU-1 zeolite is still expected to be a promising catalyst for
MTP reaction if an appropriate technology is employed.
Fig. 4. Product selectivity over EU-1, ZSM-48, ZSM-5, and beta zeolite. Reaction conditions:
T=450 °C, P=0.1 MPa (PMeOH=20 kPa), WHSV=1.5 h−1
.
heavier compounds [28], which was similar to those found for beta
zeolite [13,14]. However, from gas phase effluent components identi-
fied by GC/FID chromatograms, there is a distinct difference. An ex-
tremely small amount of C5+ hydrocarbons, especially aromatics,
was observed over EU-1 than beta zeolite (Table S1 in the Supple-
mentary information). This may be attributed to the product shape
selectivity of EU-1 zeolite. Owing to the geometrical constraints,
large molecules could not diffuse out of the narrow 10-MR channels
(4.1×5.4 Å), although the wide intersections of 10-MR channels
and 12-MR side pockets in EU-1 provided sufficiently large space for
the generation of aromatic species. Nevertheless, extremely low
amounts of aromatics could still be detected in the gas phase products.
Teketel et al. ascribed this unexpected product composition to the in-
volvement of 12-MR side pockets exposed on the outer surface of the
crystal [28], from which a small portion of aromatics could diffuse
out of EU-1 crystal without passing through the narrow 10-MR chan-
nels. Clearly, the product shape selectivity of EU-1 in MTP reaction
was mainly governed by the narrow 10-MR channels and might there-
fore make a good contribution to the high selectivity to light olefins.
Fig. 5 shows the catalytic stability of the four zeolite catalysts
during MTP reaction at 450 °C and 1.5 h−1 WHSV. As seen, all of the
catalysts exhibited almost 100% of initial methanol conversion, but
their deactivation rates were quite different. For ZSM-48, although
high initial propylene selectivity was obtained, the reduction in the
methanol conversion was accelerated after 10 h, which may be caused
by the large amount of coke deposit (40 mg-coke/g-catalyst) on its
4. Conclusions
High-silica EU-1 zeolite exhibited a higher propylene selectivity of
52% and a higher P/E ratio of 15 in MTP reaction at the operating tem-
perature of 450 °C. Besides, a substantially low amount of C5+ hydro-
carbons, especially aromatics, was yielded on EU-1 in comparison
with ZSM-48, ZSM-5, and beta zeolites. These results suggest the
potential of EU-1 zeolite as a promising catalyst in the MTP process.
Further, we believe that our study sheds light on the rational design
of a highly efficient MTP catalyst.
Acknowledgments
This work was supported by the State Key Development Program
for Basic Research of China (2012CB215002), the National Natural
Science Foundation of China (10979076, 21176255), the International
Science and Technology Cooperation and Exchange Program of China
(2010DFB40440). The authors are grateful to Dr. Zhijie Wu for his as-
sistance with the English and helpful discussions.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2012.08.011.
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