Remarkable improvement of catalytic performance in dimethyl ether to olefin reaction over CeO2-modified calcium-containing MFI type zeolite

Article abstract of DOI:10.1246/cl.2008.494

Dimethyl ether to olefin (DTO) reaction was examined over CeO ₂-modified Ca-MFI as a catalyst. The CeO₂-modified Ca-MFI (Ce/Ca-MFI) showed excellent catalytic performance to give propene as a main product. Activity was 28 times higher than conventional MFI type zeolite and seven times higher than Ca-MFI. Copyright

Full text of DOI:10.1246/cl.2008.494

494
Chemistry Letters Vol.37, No.5 (2008)
Remarkable Improvement of Catalytic Performance in Dimethyl Ether to Olefin
Reaction over CeO2-modified Calcium-containing MFI Type Zeolite
Akira Iida, Ryo Nakamura, Kenichi Komura, and Yoshihiro Sugiꢀ
Department of Materials Science and Technology, Faculty of Engineering, Gifu University, Gifu 501-1193
(Received January 30, 2008; CL-080109; E-mail: ysugi@gifu-u.ac.jp)
Dimethyl ether to olefin (DTO) reaction was examined
solid of Ca-MFI was impregnated by a EtOH solution containing
a prescribed amount of Ce(NO3)2 at room temperature. After
evaporation of EtOH, the resulting solid was recalcined at
550 ꢁC for 10 h to give CeO2-modified Ca-MFI. DTO reaction
was carried out in a fixed-bed flow reactor at 530 ꢁC under
atmospheric pressure of N2 (Details are give in Supporting Infor-
mation9). The flow rates of DME and N2 were equal to
21.2 cm3 minꢂ1. The space velocity (WHSV; weight of installed
DME per hour and per weight of catalyst) was 9.52 hꢂ1 (amount
of Ca-MFI was 0.275 g). Reaction products were analyzed
by on-line gas chromatography using a HP-5890 apparatus to
determine the conversion of DME and yields of olefins.
CeO2-modified Ca-MFI in this report is expressed as Ce(x)/
Ca-MFI, where x is the amount of CeO2 (wt %). In order to
compare catalytic activity in the DTO reaction, we defined and
used the index, (total grams of consumed DME)/(amount of
used zeolite based on Ca-MFI) (g of DME/g of Ca-MFI), as
catalytic activity.
Figure 1 shows the results of a DTO reaction over CeO2-
modified Ca-MFI. Typical MFI showed low activity (160); how-
ever, Ca-MFI showed higher activity (610). This indicates that
Ca-MFI shows good catalytic performance in DTO reaction, ow-
ing to the decrease of acidity by calcium cation.3 It was surpris-
ing that Ce(35)/Ca-MFI exhibited excellent catalytic perform-
ance. The consumed amount of DME per Ca-MFI reached about
4500, which was over seven times more active than conventional
Ca-MFI zeolite. However, CeO2-modified MFI catalyst gave re-
sults similar to Ca-MFI; further, bulk CeO2 did not exhibit cat-
alysis. These results suggest that both the existence of Ca2þ in
MFI zeolite and the modification by CeO2 seems to be quite
essential in order to achieve excellent catalytic performance in
DTO reaction.
over CeO2-modified Ca-MFI as a catalyst. The CeO2-modified
Ca-MFI (Ce/Ca-MFI) showed excellent catalytic performance
to give propene as a main product. Activity was 28 times higher
than conventional MFI type zeolite and seven times higher than
Ca-MFI.
The transformation of methanol to gasoline (MTG) or ole-
fins (MTO) has been a pivotal chemical process in the petro-
chemical industry since Mobil firstly reported the methanol to
hydrocarbon process over MFI type zeolite as catalyst.1 Light
olefins such as ethene, propene, and butene are utilized as raw
materials that can be applied for a broad range of chemical pro-
duction. Many researchers, not only academic but also industri-
al, have also made attempts towards a methanol to light olefin
process to enable more practical technology. Chang et al. have
reported that modified MFI type zeolite offers high selectivity
of light olefins and high conversion and claimed that zeolite
catalysts with small pores would be promising candidates to
obtain C2, C3, and C4 olefins as main products.2
Although MFI type zeolite is a high potential catalyst in the
MTO process, a drawback has been deactivation by severe coke
deposition. Okado et al. reported that calcium (Ca2þ)-containing
MFI type zeolite showed the good catalytic activity and lifetime
in the MTO process as due to an effective decrease of acidity by
calcium ion.3 Recently, another approach based on dimethyl
ether (DME) has also been proposed.4,5 DME to olefin (DTO)
process has been demonstrated by conventional zeolites such
as MFI and calcium-containing MFI catalysts. They generally
give propene as a principal product in 40 to 50% yield although
formation of ethene and butenes also occurs. Their advantages
are long lifetimes due to the less coke-accumulation compared
with MTO processes. Improvement of catalyst life of Ca-MFI
has demonstrated by modification with alkaline earth metal
carbonate.6 Thus, development of DTO reactions, in particular,
development of catalysts showing excellent performance is as
emerging topic in petroleum industrial chemistry.
160 MFI
610
Ca-MFI
Recently, we reported an effective improvement of shape-
selectivity in the ethylation of ethylbenzene over MFI type
zeolite and found that rare earth metal oxide-modified MFI
shows good para-selectivity due to suitable pore adjustment
and deactivation of external acid sites.7 These results encouraged
us to apply rare earth metal oxide-modified MFI type zeolite to
DTO reactions. Here, we report a remarkable improvement of
catalytic performance in the DTO reaction over CeO2-modified
Ca-MFI type zeolite.
The Ca-MFI (SiO2/Al2O3 = 200, CaO/SiO2 = 0.025) was
prepared by conventional hydrothermal synthesis,9 followed
by ion exchange to form H-type using a 0.6 M aqueous HCl
solution and then calcination at 500 ꢁC for 6 h. The resulting
Ce(40)/MFI
720
4500
Ce(35)/Ca-MFI
0
CeO2
0
1000 2000 3000 4000 5000
Catalytic activity
(g consumed DME/g Ca-MFI)
Figure 1. DTO reaction over Ce/Ca-MFI zeolite.
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.5 (2008)
495
Table 1. Properties of CeO2-modified MFI catalysts
100
Surface
area
Pore
volume
Acid
amount
Ce(35)-Ca-ZSM5
h-Peak
/ꢁC
Zeolite
80
/m2 gꢂ1 /mm3 gꢂ1 /mmol gꢂ1
Ca-ZSM5
Ca-MFI
Ce(40)/MFI
Ce(35)/Ca-MFI
350
175
228
87
75
114
0.117
0.052
0.024
307
283
307
60
40
Ca-MFI. Enhancement of pore volume in CeO2-modified
Ca-MFI was observed, because the CeO2 effectively covers
only the external surface of zeolite, resulting in deactivation of
the external acid site without choking.6 The significant decrease
in acid amount was observed in Ce(35)/Ca-MFI; however, the
acid strength corresponding to h-peak temperature remained
the same as Ca-MFI. In contrast, considerable decrease in h-peak
temperature was observed in Ce(40)/MFI. These results mean
that Ce(35)/Ca-MFI has a strong acid site similar to Ca-MFI,
although a smaller amount of acid sites: appropriate adjustment
of the acidity of Ca-MFI could be done by modification
with CeO2. However, further research is necessary to clarify
what is responsible for such high catalytic performance by CeO2
modification.
In conclusion, CeO2-modified Ca-MFI showed excellent
catalytic performance in the DTO reaction to afford propene
in 45% yield with extremely long catalytic life compared
with those of conventional Ca-MFI and typical MFI catalyst.
Appropriate deactivation of acid sites both at the external surface
of zeolite by CeO2 and in the pore by Ca cation seem to synerg-
istically enhance the catalytic performance in DTO reaction.
Further investigations are now ongoing, and we will report
elsewhere in a near future.
20
0
0
50
100
150
200
250
300
Time (h)
Figure 2. TOS in DTO reaction over Ca-MFI and Ce(35)/
Ca-MFI zeolite. Conversion of DME: for Ce(35)/Ca-MFI
and for Ca-MFI. propene (C3 olefin) yield: for Ce(35)/Ca-
MFI and for Ca-MFI.
Basic metal oxides often catalyze reformation of methanol
to give CO2, CO, and H2 gases;8 however, we could not detect
such gases in DTO reaction over Ce(35)/Ca-MFI catalyst.
This result indicates that the DTO reaction over CeO2-modified
Ca-MFI proceeds without any side reactions.
We then examined the effects of loading amount of CeO2
in the DTO reaction over Ce(x)/Ca-MFI (x ¼ 0 to 50) (see
Figure S3 in Supporting Information).9 Increased loading of
CeO2 in Ca-MFI showed gradual improvement in activity: 880
(x ¼ 10), 1430 (x ¼ 20), and 1580 (x ¼ 30), the maximum activ-
ity can be observed at 35 wt% loading of CeO2. However, under
high loading of CeO2, the Ce(40) and Ce(50)/Ca-MFI activity
declined to 2950 and 1430, respectively. These results show that
the catalytic activity depends on the loading amount and that
an appropriate amount of CeO2 triggered excellent catalytic
activity.
Figure 2 shows the results of time-on-stream (TOS) over
Ca-MFI and Ce(35)/Ca-MFI, respectively. The distribution of
products (ethene, propene, and butenes) over Ce(35)/Ca-MFI
is similar to that of Ca-MFI (only yield of C3 olefin in
Figure 2). The complete conversion of DME over Ca-MFI took
about 40 h, and then the activity was gradually decreased and
completely lost at 90 h. The yield of propene also declined with
decreasing conversion of DME. In contrast, the Ce(35)/Ca-MFI
proved to keep catalytic activity over 200 h (>99% conversion
of DME) to give propene in 45% yield as a main product. It is
obvious that Ce(35)/Ca-MFI shows excellent catalytic perform-
ance in DTO reaction.
References and Notes
1
2
3
Handbook of Zeolite Science and Technology, ed. by S. M.
Auerbach, K. A. Carrado, P. K. Dutta, Marcel Dekker,
Inc., New York, 2003.
a) C. D. Chang, Cat. Rev.-Sci. Eng. 1984, 26, 323. b) C. D.
Chang, C. T. W. Chu, R. F. Socha, J. Catal. 1984, 86, 289.
c) C. T. W. Chu, C. D. Chang, J. Catal. 1984, 86, 297.
a) H. Okado, H. Shoji, K. Kawamura, Y. Kotoku, Y.
Yamazaki, T. Sano, H. Takaya, Nippon Kagaku Kaishi
1987, 25. b) H. Okado, T. Sano, K. Matsuzaki, K.
Kawamura, K. Hashimoto, H. Watanabe, H. Takaya, Nippon
Kagaku Kaishi 1987, 791. c) H. Okado, H. Shoji, K.
Kawamura, Y. Shiomi, K. Fujisawa, H. Hagiwara, H.
Takaya, Nippon Kagaku Kaishi 1987, 962.
4
K. Wakui, K. Furusawa, Jpn Kokai Tokkyo Koho 2005-
60355.
We note that the DTO reaction over CeO2-modified Ca-MFI
has a similar reaction path as over Ca-MFI, because the distribu-
tion of produced olefins such as ethene, propene, and butenes is
not significantly different from that of Ca-MFI, and CeO2 onto
the zeolite did not affect the catalysis.
In order to clarify why CeO2-modified Ca-MFI shows high
performance in DTO reactions, N2 adsorption and NH3-TPD
analyses were undertaken (Table 1). Modification by CeO2
reduces the surface area; especially, Ce(40)/MFI showed
remarkably decreased surface area compared to that of Ce(35)/
5
6
H. Itoh, Jpn Kokai Tokkyo Koho 2005-104912.
T. Sano, T. Murakami, K. Suzuki, S. Ikai, H. Okado, K.
Kawamura, H. Hagiwara, H. Takaya, Appl. Catal. 1987,
33, 209.
Y. Sugi, Y. Kubota, K. Komura, N. Sugiyama, M. Hayashi,
J. H. Kim, G. Seo, Appl. Catal., A 2006, 299, 157.
K. Takehira, Shokubai 2001, 43, 244.
Supporting Information is available electronically on the
CSJ-Journal Web site, http://www.csj.jp/journals/chem-lett/
index. html.
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8
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Published on the web (Advance View) March 29, 2008; doi:10.1246/cl.2008.494