Conversion of ethanol to propylene over HZSM-5 type zeolites containing alkaline earth metals

Article abstract of DOI:10.1016/j.apcata.2010.05.032

Protonated ZSM-5 type zeolites containing alkaline earth metals (M-HZSM-5, M: alkaline earth metal) were prepared under various synthesis conditions and their catalytic performance in the conversion of ethanol to light olefins, especially propylene (C₃H₆), were investigated in detail. The C₃H₆ yield and the catalytic stability were strongly dependent on M/Al and SiO₂/Al₂O₃ ratios as well as on the reaction conditions. Among M-HZSM-5 zeolites, the Sr-HZSM-5 zeolite having a SiO₂/Al₂O₃ ratio of 184 and a Sr/Al ratio of 0.1 exhibited the highest C₃H₆ yield of ca. 32 C-% and a high catalytic stability at the reaction condition of 500 °C and W/F value of 0.03 g_cat/ml/min.

Full text of DOI:10.1016/j.apcata.2010.05.032

Applied Catalysis A: General 383 (2010) 89–95
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Conversion of ethanol to propylene over HZSM-5 type zeolites containing
alkaline earth metals
Daisuke Gotoa , Yasumitsu Haradaa , Yoshiyasu Furumotoa , Atsushi Takahashib , Tadahiro Fujitanib ,
Yasunori Oumia, Masahiro Sadakanea, Tsuneji Sanoa,∗
a Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
b Research Institute for Innovation in Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8569, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Protonated ZSM-5 type zeolites containing alkaline earth metals (M-HZSM-5, M: alkaline earth metal)
were prepared under various synthesis conditions and their catalytic performance in the conversion
of ethanol to light olefins, especially propylene (C3H6), were investigated in detail. The C3H6 yield and
the catalytic stability were strongly dependent on M/Al and SiO2/Al2O3 ratios as well as on the reaction
conditions. Among M-HZSM-5 zeolites, the Sr-HZSM-5 zeolite having a SiO2/Al2O3 ratio of 184 and a
Sr/Al ratio of 0.1 exhibited the highest C3H6 yield of ca. 32 C-% and a high catalytic stability at the reaction
condition of 500 ◦C and W/F value of 0.03 gcat/ml/min.
Received 24 February 2010
Received in revised form 7 May 2010
Accepted 20 May 2010
Available online 31 May 2010
Keywords:
Ethanol
ZSM-5
© 2010 Elsevier B.V. All rights reserved.
Propylene
Alkaline earth metal
Strontium
1. Introduction
ing and/or aromatization of higher olefins. Since the cracking of
light olefins proceeds at high temperatures, the thermal stability of
Light olefins such as ethylene and propylene are essential raw
materials for the petrochemical industry. In recent years, the
demand for propylene has grown considerably faster than that for
ethylene because of greater needs for propylene derivatives such as
propylene oxide and polypropylene. Propylene is mainly produced
as a co-product of ethylene by the steam cracking of naphtha. From
the perspective of increasing oil prices and environmental protec-
tion, the development of other routes for propylene production,
especially from bio-ethanol by the fermentation of biomass, has
recently attracted considerable attention. The production of light
olefins from bio-ethanol and renewable biomass is an example of a
carbon-neutral process. Although the production of hydrocarbons
such as ethylene, gasoline, and aromatics from ethanol using solid
catalysts has been reported by many researchers [1–10], there are
only a few reports concerning the production of light olefins, espe-
cially propylene [11–15], and the catalytic activity and stability of
catalysts are insufficient for industrial processes.
catalysts is a crucial factor.
We have already investigated the production of light olefins
from methanol and have developed excellent HZSM-5 zeolite cat-
alysts containing alkaline earth metals (M-HZSM-5, M: alkaline
earth metal). The M-HZSM-5 zeolites could be used at high tem-
peratures of 500–600 ◦C, produced high yields of ethylene and
propylene of more than 60 C-%, and had a long catalyst life of over
2000 h [16]. In this study, we investigated the potential of M-HZSM-
5 for ethanol conversion to light olefins, especially propylene, and
clarified the difference between the reaction behaviors of methanol
and ethanol conversions over M-HZSM-5 zeolite.
2. Experimental
2.1. Synthesis of HZSM-5 zeolites containing alkaline earth metals
Protonated ZSM-5 type zeolites containing alkaline earth met-
als (M-HZSM-5, M: alkaline earth metal) were synthesized as
follows. Aluminum nitrate (Al(NO3)3·9H2O, Wako Pure Chemical
Ind. Ltd., Japan), colloidal silica (SiO2 = 30.5 wt%, Na2O = 0.4 wt%,
H2O = 69.1 wt%, Cataloid SI-30, Catalysts & Chemicals Ind. Co.
Ltd., Japan) and tetrapropylammonium bromide (TPABr, Tokyo
Chemical Ind. Co. Ltd., Japan) were added to a stirred mix-
ture of alkaline earth metal acetate (Tokyo Chemical Ind. Co.
Ltd., Japan) and sodium hydroxide (Kanto Chemical Co. Inc.,
It is well known that the conversion of ethanol over a zeolite
catalyst is similar to that of methanol and involves the following
pathways: (1) the dehydration of ethanol into ethylene, (2) the
oligomerization of ethylene into higher olefins, and (3) the crack-
∗
Corresponding author. Tel.: +81 82 424 7607; fax: +81 82 424 5494.
E-mail address: tsano@hiroshima-u.ac.jp (T. Sano).
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.05.032

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D. Goto et al. / Applied Catalysis A: General 383 (2010) 89–95
Japan) in deionized water. The hydrogel composition was as fol-
lows: SiO2/Al2O3 = 40–600, OH−/SiO2 = 0.1–0.2, TPABr/SiO2 = 0.1,
H2O/SiO2 = 40, and M/Al = 0.05–0.5. The resultant hydrogel was
transferred into a 300-ml stainless-steel autoclave and stirred at
160 ◦C under autogenous pressure for 16 h. The precipitated crys-
tals obtained were washed with deionized water, dried at 120 ◦C
for one night, and calcined at 500 ◦C for 10 h to remove the organic
cations occluded in the zeolite framework. The zeolite was proto-
nated in a 0.6 mol/dm3 hydrochloric acid solution at 60 ◦C for 24 h,
and calcined in air at 500 ◦C for 6 h.
2.2. Characterization
X-ray diffraction (XRD) patterns of the solid products were
obtained using a powder X-ray diffractometer (Bruker D8 Advance)
with graphite monochromatized Cu K␣ radiation at 40 kV and
30 mA. Si/Al and M/Al ratios were determined by X-ray fluores-
cence (XRF, Philips PW 2400). A fixed amount of the sample (0.5 g)
was fused with 5 g of dilithium tetraborate (Li2B4O7) at 1100 ◦C. The
crystal morphology was observed by scanning electron microscopy
(SEM, JEOL JSM-6320FS). The thermal analysis was carried out using
a TG/DTA apparatus (SSC/5200 Seiko Instruments). The sample (ca.
7 mg) was heated in a flow of air (50 ml/min) at 10 ◦C/min from
room temperature to 800 ◦C. 27Al MAS NMR spectra were recorded
using a 7-mm diameter zirconia rotor on a Bruker Avance DRX-
400 spectrometer at 100.6 MHz spinning at 6 kHz. The spectra were
obtained with 2.3-␮s pulses, 1-s recycle delay, and 4000 scans.
Al(NO3)3·9H2O was used as a chemical shift reference. Prior to 27Al
MAS NMR measurement, the sample was moisture-equilibrated
over a saturated solution of NH4Cl for 24 h. Nitrogen adsorption
isotherms were obtained at −196 ◦C using a conventional volu-
metric apparatus (BELSORP 28SA, Bel Japan). Prior to adsorption
measurements, the calcined samples (ca. 0.1 g) were evacuated at
400 ◦C for 10 h. IR spectra were recorded on a FT-IR spectrometer
(JEOL JIR-7000) with a resolution of 4 cm−1 at room temperature.
For measurements in the OH groups stretching region, the sam-
ple was pressed into a self-supporting thin wafer (ca. 6.4 mg/cm2)
and placed into a quartz IR cell equipped with CaF2 windows. Prior
to measurement, each sample was dehydrated under vacuum at
400 ◦C for 2 h. The acidity and distribution of zeolites were mea-
sured by the temperature programmed desorption of ammonia
(NH3-TPD, CAT-B-82 NH3-TPD, Bel Japan). Helium was used as a
carrier gas. The temperature range was from 100 to 600 ◦C with the
heating rate of 10 ◦C/min.
Fig. 1. Influence of SiO2/Al2O3 ratio of HZSM-5 on C2H4 (᭹), C3H6 (ꢀ), and C4H8 (ꢁ)
yields. Reaction condition: temp. = 500 ◦C, W/F = 0.0025 gcat/ml/min.
quartz wool placed at the center of a quartz reactor with a 10-
mm inner diameter. A thermocouple inserted into the center of the
catalyst bed was used to measure the temperature during the reac-
tion. The catalyst was activated at 500 ◦C for 1 h in flowing nitrogen
before the reaction. Ethanol (>99.5%, Wako Pure Chemical Ind. Ltd.,
Japan) was pumped into the vaporizer and mixed with N2 at a
total flow rate of 20 ml/min (C2H5OH/N2 = 50/50 mol%). The reac-
tion temperature was increased stepwise (50 ◦C) from 400 to 600 ◦C
and maintained at each temperature for 1 h. The products obtained
were analyzed on-line using gas chromatographs (Shimadzu GC-
14) equipped with TCD- and FID-type detectors. InertCap 1701 and
Gasukuropack-54 columns were used.
3. Results and discussion
3.1. Ethanol conversion over HZSM-5
First, in order to clarify the difference between the reaction
behaviors of methanol and ethanol conversions, HZSM-5 zeo-
lites with various SiO2/Al2O3 ratios were prepared and used for
ethanol conversion. As listed in Table 1, the BET surface area of the
obtained HZSM-5 zeolites was larger than 300 m2/g and the crys-
tal size was 0.1–6.0 ␮m. Fig. 1 shows the relationship between the
SiO2/Al2O3 ratio and the light olefin yields at the reaction condi-
tion of temp. = 500 ◦C and W/F = 0.0025 gcat/ml/min. The C3H6 and
C4H8 yields increased with a decrease in the SiO2/Al2O3 ratio and
2.3. Ethanol conversion
Ethanol conversion was carried out at 400–600 ◦C and W/F val-
ues of 0.0025–0.04 gcat/ml/min in an atmospheric pressure flow
system. A certain amount of zeolite (12–24 mesh) was retained by
Table 1
Synthesis conditions and characteristics of HZSM-5 zeolites.
Sample no.
Synthesis mixturea
SiO2/Al2O3 ratio
Product
OH−/SiO2
SiO2/Al2O3 ratiob
Surface areac (m2/g)
Particle size (␮m)
1
2
3
4
5
6
7
8
40
50
75
100
150
200
400
600
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0.1
47
52
76
107
146
184
354
514
363
358
377
365
361
357
387
395
0.1–0.2
1–2
2–5
3–4
3–4
4–6
3–4
4–5
a
Synthesis conditions: TPABr/SiO2 = 0.1, temp. = 160 ◦C, time = 16 h.
Determined by XRF.
Determined by the BET method.
b
c

D. Goto et al. / Applied Catalysis A: General 383 (2010) 89–95
91
Fig. 2. Conversion of ethanol to light olefins over HZSM-5 with SiO2/Al2O3 ratios of 52 (᭹), 76 (ꢂ), and 184 (ꢁ). Temp. = 500 ◦C.
reached the maximum values at the SiO2/Al2O3 ratio of ca. 50,
while the C2H4 yield dramatically decreased with a decrease in the
SiO2/Al2O3 ratio. The relationship between the SiO2/Al2O3 ratio and
the light olefin yield was considerably different from that observed
in the methanol conversion, in which ethylene and propylene were
more effectively produced on the siliceous zeolites [16]. The results
suggest that the oligomerization of ethylene produced by the dehy-
dration of ethanol does not easily occur on siliceous HZSM-5 zeolite
due to smaller Brönsted acid sites.
As propylene is produced by the cracking of higher olefins, it is
reasonable to consider that the product distribution of hydrocar-
bons obtained by ethanol conversion is also strongly dependent
on the contact time as well as on the SiO2/Al2O3 ratio. There-
fore, the influence of W/F value on the product distribution of
ethanol conversion was investigated using HZSM-5 zeolites with
various SiO2/Al2O3 ratios. Typical results for HZSM-5 zeolites with
SiO2/Al2O3 ratios of 52, 76, and 184 are shown in Fig. 2. The C2H4
and C3H6 yields were strongly dependent on the W/F value. The
C2H4 yield decreased with an increase in W/F value, while the
C3H6 yield showed the maximum value for HZSM-5 zeolites with
SiO2/Al2O3 ratios of 76 and 184. This indicates that the optimum
W/F value for the selective production of propylene is related to the
SiO2/Al2O3 ratio of the HZSM-5 zeolite employed.
stability is related to the dealumination of the HZSM-5 zeolite.
Therefore, the degree of dealumination was measured by 27Al MAS
NMR.
Fig. 4 shows the 27Al MAS NMR spectra of HZSM-5 zeolites with
SiO2/Al2O3 ratios of 52 and 184 before and after the reaction. In
all spectra, the peak assigned to tetrahedrally coordinated frame-
work aluminums was observed at ca. 54 ppm. However, there was a
large difference in the degree of dealumination, that is, the HZSM-5
zeolite with a SiO2/Al2O3 ratio of 52 exhibited a higher degree of
dealumination than that with a SiO2/Al2O3 ratio of 184. Therefore,
the large difference in the time on stream of C3H6 yield is attributed
to the difference in the degree of dealumination. From a standpoint
of the stability of acid sites against steaming during the reaction,
these results indicate that the siliceous HZSM-5 zeolite is suitable
for the ethanol conversion to light olefins, although a larger W/F
value is required. The high steam stability of siliceous HZSM-5 is
consistent with our previous results of dealumination of HZSM-5
zeolite by steaming [17,18]. In order to improve the catalyst life at
high reaction temperatures, the resistance against steaming must
be improved. Therefore, we attempted to develop siliceous HZSM-5
zeolite catalysts in the following experiments.
In general, the deactivation of a zeolite catalyst occurs pre-
dominantly because of two causes: one is the poisoning of active
sites, Brönsted acid sites, due to the accumulation of carbonaceous
deposits, and the other is the structure degradation of the zeolite
due to dealumination of the framework. Since water is produced
as a co-product in the ethanol conversion, the zeolite catalyst is
exposed to a moisture-rich atmosphere during the reaction. Dealu-
mination of the zeolite framework is accelerated in a moisture-rich
atmosphere at high temperatures, resulting in the severe deacti-
vation of the zeolite catalyst. Therefore, the catalytic stability of
HZSM-5 zeolite was investigated. Fig. 3 shows the time on stream
of the C3H6 yield over HZSM-5 zeolites with SiO2/Al2O3 ratios of
52 and 184. Because we wanted to keep the initial C3H6 yield simi-
lar, we set the W/F values to 0.0125 and 0.03 g/ml/min for HZSM-5
zeolites with SiO2/Al2O3 ratios of 52 and 184, respectively. As seen
in Fig. 3, the C3H6 yield for the HZSM-5 zeolite with a SiO2/Al2O3
ratio of 52 gradually decreased with the time on stream, whereas
only a slight decrease was observed for that with a SiO2/Al2O3 ratio
of 184. Although there was a large difference in the W/F value, no
difference was observed in the amount of carbonaceous deposits
after the reaction for 8 h as evaluated by TG analysis, that is, 3.2
and 3.1 wt% for HZSM-5zeolites with SiO2/Al2O3 ratios of 52 and
184, respectively. This suggests that the difference in the catalytic
Fig. 3. Time on stream of C3H6 yield on HZSM-5 with SiO2/Al2O3 ratios of 52
(ꢀ) and 186 (᭹). Reaction condition: temp. = 550 ◦C, W/F = 0.0125 (ꢀ) and 0.03 (᭹)
gcat/ml/min.

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D. Goto et al. / Applied Catalysis A: General 383 (2010) 89–95
Fig. 4. 27Al MAS NMR spectra of HZSM-5 with SiO2/Al2O3 ratios of (a and b) 52 and
(c and d) 186 before (a and c) and after (b and d) reaction.
3.2. Ethanol conversion over M-HZSM-5
We investigated the potential catalytic activity of M-HZSM-
5 zeolites modified with alkaline earth metals; such materials
showed an excellent performance in methanol conversion to light
olefins. On the basis of the above result for HZSM-5 zeolites,
siliceous M-HZSM-5 zeolites were synthesized and utilized for
ethanol conversion. Table 2 lists the hydrothermal synthesis con-
ditions and the characteristics of various M-HZSM-5 zeolites. The
prepared M-HZSM-5 zeolite had a well-defined ZSM-5 type zeolite
structure, as demonstrated by their XRD patterns (Fig. 5). There
was no diffraction peaks other than those of the ZSM-5 zeolite.
The BET surface area measured by N2 adsorption was larger than
300 m2/g and was the same as that of the HZSM-5 zeolite. The typ-
ical SEM images of various M-HZSM-5 zeolites are also shown in
Fig. 5. The M/Al ratio in M-HZSM-5 zeolite was changed from 0.05 to
0.5. Mg-HZSM-5 zeolites with Mg/Al ratios of over 0.05 could not
Fig. 5. XRD patterns and SEM images of (a) HZSM-5 (Sample no. 6), (b) Mg-HZSM-5
(no. 9), (c) Ca-HZSM-5 (no. 11), (d) Sr-HZSM-5 (no. 15), and (e) Ba-HZSM-5 (no. 21).
be synthesized. To clarify the chemical state of aluminum in the
M-HZSM-5 zeolite, 27Al MAS NMR spectra were measured. Only a
sharp peak at ca. 54 ppm was observed in all spectra (not shown),
which is the characteristic resonance of tetrahedrally coordinated
framework aluminum. No peak assigned to non-framework alu-
minum (extraframework aluminum) was observed around 0 ppm.
Thus, the results clearly showed that all aluminums in the M-HZSM-
5 zeolite are present in the zeolitic framework.
Considering that high reaction temperature above 500 ◦C favors
the production of light olefins, and that experiments using C2–C4
Table 2
Synthesis conditions and characteristics of alkaline earth metal containing HZSM-5 zeolites (M-HZSM-5).
Sample no.
Synthesis mixturea
SiO2/Al2O3 ratio
Productb
a
M/Al
SiO2/Al2O3 ratio
M/Ala
Surface areac (m2/g)
Particle size (␮m)
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
200
200
200
200
200
200
200
200
200
150
100
200
200
200
200
0.05 (Mg)
0.05 (Ca)
0.125 (Ca)
0.25 (Ca)
0.50 (Ca)
0.05 (Sr)
0.125 (Sr)
0.25 (Sr)
0.50 (Sr)
0.125 (Sr)
0.125 (Sr)
0.05 (Ba)
0.125 (Ba)
0.25 (Ba)
0.50 (Ba)
198
206
200
213
202
202
203
202
211
104
153
212
211
215
221
0.06
0.10
0.14
0.31
0.52
0.04
0.10
0.21
0.46
0.09
0.10
0.06
0.13
0.26
0.50
371
374
367
373
364
377
374
368
361
354
365
364
351
353
345
2–3
2.5–3
3–4
2–5
3–4
5–10
3–5
2–3
6–9
3–5
3–5
4–8
3–4
2–3
2–6
a
Synthesis conditions: TPABr/SiO2 = 0.1, OH−/SiO2 = 0.1, temp. = 160 ◦C, time = 16 h.
Determined by XRF.
Determined by the BET method.
b
c

D. Goto et al. / Applied Catalysis A: General 383 (2010) 89–95
93
Fig. 8. NH3-TPD curves of (—) HZSM-5 (Sample no. 6), (- - -) Sr-HZSM-5 (no. 15), and
(· · ·) Sr-HZSM-5 (no. 17).
Fig. 6. Influence of M/Al ratio of M-HZSM-5 on C3H6 yield over Mg-HZSM-5 (ꢃ), Ca-
HZSM-5 (ꢀ), Sr-HZSM-5 (ꢀ), and Ba-HZSM-5 (ꢁ). Reaction condition: temp. = 500 ◦C,
W/F = 0.03 gcat/ml/min.
ethylene oligomerization probably due to a decrease in the number
of strong Brönsted acid sites of HZSM-5 zeolite upon the modifica-
tion with alkaline earth metals. For the Sr-HZSM-5 zeolite with a
Sr/Al ratio of 0.1, the slight decrease in the intensity of the peak
at around 320 ◦C assigned to strong acid sites was confirmed from
NH3-TPD measurements. There was a considerable decrease in the
peak intensity observed for the Sr-HZSM-5 zeolite with Sr/Al ratio
of 0.46 (Fig. 8).
From the standpoint of the catalytic stability of the Sr-HZSM-5
zeolite, we investigated the time on stream of C3H6 yield. HZSM-5
zeolite was also used for comparison. As shown in Fig. 9, no change
in the C3H6 yield was observed for Sr-HZSM-5 zeolite, while a slight
decrease was observed for HZSM-5 zeolite, indicating the higher
catalytic stability of the Sr-HZSM-5 zeolite. To verify this, we per-
formed the 27Al MAS NMR measurements. Fig. 10 shows the 27Al
MAS NMR spectra of HZSM-5 and Sr-HZSM-5 zeolites before and
after the reaction for 8 h. A considerable decrease in the peak inten-
sity at ca. 54 ppm was observed for HZSM-5 zeolite, while only
a slight decrease was seen for Sr-HZSM-5 zeolite. This indicates
that the high catalytic stability of Sr-HZSM-5 is due to a high resis-
olefins as feed instead of ethanol showed the cracking of the olefins
to be predominant and the aromatization of the olefins to be sup-
pressed at high temperatures, we applied M-HZSM-5 zeolites for
ethanol conversion at high temperatures. Fig. 6 shows the relation-
ship between the M/Al ratio and the C3H6 yield for the M-HZSM-5
zeolite with a SiO2/Al2O3 ratio of ca. 200 at 500 ◦C. The C3H6 yield
increased with an increase in the M/Al ratio and reached at max-
imum value at a M/Al ratio of ca. 0.1. Among M-HZSM-5 zeolites,
the Sr-HZSM-5 zeolite showed the highest C3H6 yield of ca. 32 C-%.
Further increase in the M/Al ratio caused considerable decrease in
the C3H6 yield. The M/Al ratio dependence of the C3H6 yield was
remarkably different from that of methanol conversion, in which
high C3H6 yield was only obtained at an M/Al ratio of 2–2.5 [16].
The improvement of the C3H6 yield was not observed by chang-
ing the SiO2/Al2O3 ratio from 200 to 100 and 150 (not shown).
As shown in Fig. 7, the decrease in the C3H6 yield was due to a
considerable increase in the C2H4 yield, indicating suppression of
Fig. 7. Influence of Sr/Al ratio of Sr-HZSM-5 on C2H4 (ꢀ), C3H6 (ꢂ), and C4H8 (ꢁ)
yields. Reaction condition: temp. = 500 ◦C, W/F = 0.03 gcat/ml/min.
Fig. 9. Time on stream of C3H6 yield on (᭹) Sr-HZSM-5 (Sample no. 15) and (ꢀ)
HZSM-5 (no. 6). Reaction condition: temp. = 500 ◦C, W/F = 0.03 gcat/ml/min.

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D. Goto et al. / Applied Catalysis A: General 383 (2010) 89–95
Fig. 11. Influence of W/F on C3H6 yield for (᭹) HZSM-5 (Al), (ꢁ) HZSM-5 (Ga), and
(ꢂ) HZSM-5 (Fe). Temp. = 500 ◦C.
Fig. 10. 27Al MAS NMR spectra of (a and b) HZSM-5 (Sample no. 2) and (c and d)
Sr-HZSM-5 (no. 15) before (a and c) and after (b and d) reaction.
tance to steaming. The deposition of carbonaceous materials on
Sr-HZSM-5 (1.7 wt%) was also suppressed by modification with Sr
as compared with HZSM-5 (3.1 wt%).
From the above results, it was found that the catalytic per-
formance of the HZSM-5 zeolite was considerably improved by
modification with Sr. However, the optimum amount of Sr is very
small (Sr/Al ratio of 0.1), suggesting a slight decrease in the number
of Brönsted acid sites. Therefore, HZSM-5 zeolites with a SiO2/Al2O3
ratio of more than 200 were prepared (Table 1, Sample nos. 7
and 8) and used for ethanol conversion. However, the C3H6 yields
were 21.7 C-% for a SiO2/Al2O3 ratio of 354 and 10.2 C-% for a
SiO2/Al2O3 ratio of 514 at reaction condition of 500 ◦C and W/F
value of 0.03 gcat/ml/min. This strongly indicates that the modifi-
cation with Sr does not only reduce the number of strong Brönsted
acid sites.
It is well recognized that the framework aluminum of ZSM-
5 zeolite can be substituted by Ga and Fe atoms, resulting in
a decrease in the acid strength of Brönsted acid sites; HZSM-
5(Al) > HZSM-5(Ga) > HZSM-5(Fe) [19]. To clarify the influence of
the acid strength of Brönsted acid sites on ethanol conversion,
siliceous HZSM-5(Ga) and HZSM-5(Fe) zeolites were prepared and
utilized for ethanol conversion. As shown in Fig. 11, although the
reactions were carried out at various W/F values, the HZSM-5(Ga)
zeolite with a SiO2/Ga2O3 ratio of 202 and the HZSM-5(Fe) zeo-
lite with a SiO2/Fe2O3 ratio of 191 did not show higher C3H6 yield
as compared to the HZSM-5(Al) zeolite with a SiO2/Al2O3 ratio of
184. This suggests that the higher performance of Sr-HZSM-5 zeo-
lite is not only due to the control of acidity by modification with Sr
but also to other factors, probably physically blocking a part of the
channel structure of the ZSM-5 zeolite.
Fig. 12. N2 adsorption isotherms for (ꢀ) HZSM-5 (Sample no. 6), (ꢀ) Sr-HZSM-5
(no. 15), and (ꢁ) Sr-HZSM-5 (no. 17).
Sr cations in channels. Probably, Sr cations exist at the intersections
of straight and sinusoidal channels, resulting in the suppression of
aromatization of higher olefins, which needs a large space. How-
ever, we could not clearly explain the reasons for the considerable
improvement of the C3H6 yield and the catalytic stability of the
HZSM-5 zeolite modified with a small amount of Sr at the present
time. A further study is now in progress.
4. Conclusions
Aluminous HZSM-5 zeolites exhibited a high degree of dealu-
mination during ethanol conversion into light olefins, indicating
that the siliceous HZSM-5 zeolite is suitable for ethanol conver-
sion, although a large W/F value is required. We developed siliceous
HZSM-5 zeolite catalysts modified with alkaline earth metals (M-
HZSM-5, M: alkaline earth metal). The C3H6 yield and the catalytic
stability of this zeolite were strongly dependent on M/Al and
SiO2/Al2O3 ratios as well as on the reaction conditions. Among
the M-HZSM-5 zeolites, the Sr-HZSM-5 zeolite having a SiO2/Al2O3
ratio of 184 and a Sr/Al ratio of 0.1 exhibited the highest C3H6 yield
of ca. 32% and a high catalytic stability at the reaction condition of
The location of Sr cations in the channel structure of the HZSM-5
zeolite was investigated by preliminary Rietveld refinement based
on powder XRD data. However, the location of Sr cations could not
be completely evaluated at the present time due to the small Sr
content (Sr/Al ratio: 0.1). Therefore, the change in the zeolitic pore
volume was measured by N2 adsorption experiments. Fig. 12 shows
N2 adsorption isotherms of HZSM-5 and Sr-HZSM-5 zeolites. There
was no difference in the amount of N2 adsorbed between HZSM-5
and Sr-HZSM-5 with a Sr/Al ratio of 0.46, suggesting an absence of

D. Goto et al. / Applied Catalysis A: General 383 (2010) 89–95
95
500 ◦C and W/F value of 0.03 gcat/ml/min. The higher performance
of Sr-HZSM-5 zeolite is due to not only the control of acidity by
the modification with Sr but also to other factors, probably phys-
ically blocking a part of the channel structure of ZSM-5 zeolite by
Sr cations at the intersections of straight and sinusoidal channels.
[5] A.T. Aguaya, A.G. Gayubo, A.M. Tarrio, A. Atutxa, J. Bilbao, J. Chem. Technol.
Biotechnol. 77 (2002) 211–216.
[6] M. Inaba, K. Murata, M. Saito, I. Takahashi, React. Kinet. Catal. Lett. 88 (2006)
135–142.
[7] V. Calsavara, M.L. Baesso, N.R.C. Fernandez-Machado, Fuel 87 (2008)
1628–1636.
[8] D. Zhang, R. Wang, X. Yang, Catal. Lett. 124 (2008) 384–391.
[9] F. Ferreria-Madeira, N.S. Gnep, P. Magnoux, S. Maury, N. Gadran, Appl. Catal. A:
Gen. 367 (2009) 39–46.
[10] J. Ouyang, F. Kong, G. Su, Y. Hu, Q. Song, Catal. Lett. 132 (2009) 64–74.
[11] H. Oikawa, Y. Shibata, K. Inazu, Y. Iwase, K. Murai, S. Hyodo, G. Kobayashi, T.
Baba, Appl. Catal. A: Gen. 312 (2006) 181–185.
[12] K. Murata, M. Inaba, T. Takahara, J. Jpn. Petrol. Inst. 51 (2008) 234–239.
[13] Q. Zhu, J.N. Kondo, S. Inagakli, T. Tatsumi, Top. Catal. 52 (2009) 1272–1280.
[14] T. Yamazaki, N. Kikuchi, M. Katoh, Y. Okada, T. Yoshikawa, M. Wada, J. Jpn.
Petrol. Inst. 52 (2009) 234–247.
Acknowledgement
This work was supported by a New Energy and Industrial Tech-
nology Development Organization (NEDO) grant.
References
[15] Z. Song, A. Takahashi, N. Mimura, T. Fujitani, Catal. Lett. 131 (2009) 364–369.
[16] T. Sano, Y. Kiyozumi, S. Shin, J. Jpn. Petrol. Inst. 35 (1992) 429–440.
[17] T. Sano, K. Suzuki, H. Shoji, S. Ikai, K. Okabe, T. Murakami, S. Shin, H. Hagiwara,
H. Takaya, Chem. Lett. (1987) 1421–1424.
[18] T. Sano, N. Yamashita, Y. Iwami, K. Takeda, Y. Kawakami, Zeolites 16 (1996)
258–264.
[1] V.R. Choudhary, V.S. Nayak, Zeolites 5 (1985) 325–328.
[2] S.K. Saha, S. Sivasanker, Catal. Lett. 15 (1992) 413–418.
[3] E. Costa, A. Uguina, J. Aguado, P.J. Hernandez, Ind. Eng. Chem. Process. Des. Dev.
24 (1985) 239–244.
[4] A.K. Talukdar, K.G. Bhattacharyya, S. Sivasanker, Appl. Catal. A: Gen. 148 (1997)
357–371.
[19] C.T.-W. Chu, C.D. Chang, J. Phys. Chem. 89 (1985) 1569–1571.