Dehydrogenation and Isomerization of Butane over Cr Catalysts Supported on H-SSZ-35 Type Zeolites

Article abstract of DOI:10.1246/bcsj.77.381

The dehydrogenation and isomerization of butane to isobutene over Cr catalysts supported on zeolites were investigated. Although a zeolite support, especially with a low Si/Al₂ ratio, favors the cracking of butane over its dehydrogenation and isomerization, due to strong solid acidity, the loading of Cr on a zeolite support enhances the dehydrogenation and isomerization of butane. H-SSZ-35 type zeolite, which has a one-dimensional cage-type channel structure, was hydrothermally synthesized using cis,cis,cis-N-methylhexahydrojulolidinium hydroxide as a structure-directing agent (SDA). We found that Cr/H-SSZ-35 (Si/Al₂ = 500) showed moderate butane conversion and isobutene selectivity. As a result, the yield of isobutene (conversion of butane x selectivity of isobutene) was the highest among the catalysts used in this study. Its activity at 500 °C remained unchanged for 6 h. Our evidence suggests that butane was dehydrogenated over the zeolite support or Cr₂O₃ particles, and a proportion of the dehydrogenated products were isomerized to isobutene over the zeolite support.

Full text of DOI:10.1246/bcsj.77.381

ꢀ 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 381–386 (2004)
381
Dehydrogenation and Isomerization of Butane over Cr Catalysts
Supported on H-SSZ-35 Type Zeolites
ꢀ
Hideaki Hamada, and Yohei Kurata
Megumu Inaba, Kazuhisa Murata, Masahiro Saito, Isao Takahara, Naoki Mimura,
National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565
Received February 27, 2003; E-mail: mg.inaba@aist.go.jp
The dehydrogenation and isomerization of butane to isobutene over Cr catalysts supported on zeolites were inves-
tigated. Although a zeolite support, especially with a low Si/Al2 ratio, favors the cracking of butane over its dehydrogen-
ation and isomerization, due to strong solid acidity, the loading of Cr on a zeolite support enhances the dehydrogenation
and isomerization of butane. H-SSZ-35 type zeolite, which has a one-dimensional cage-type channel structure, was hydro-
thermally synthesized using cis,cis,cis-N-methylhexahydrojulolidinium hydroxide as a structure-directing agent (SDA).
We found that Cr/H-SSZ-35 (Si/Al2 = 500) showed moderate butane conversion and isobutene selectivity. As a result,
the yield of isobutene (conversion of butane ꢁ selectivity of isobutene) was the highest among the catalysts used in this
study. Its activity at 500 ꢂC remained unchanged for 6 h. Our evidence suggests that butane was dehydrogenated over the
zeolite support or Cr2O3 particles, and a proportion of the dehydrogenated products were isomerized to isobutene over the
zeolite support.
Isobutene is an important intermediate for many common
petrochemicals and plastics, and in order to synthesize isobu-
tene, the dehydrogenation of isobutane1–3 and the skeletal iso-
merization of butenes4–6 had been studied quite extensively.
For the dehydrogenation of isobutane, it has been reported that
Cr oxide-based catalysts are effective. For example, Hoang et
al. studied the dehydrogenation of isobutane over Cr2O3 sup-
ported on various rare earth materials (Cr2O3 supported on
La2(CO3)3, Sm2(CO3)3, and Pr2(CO3)3).1 Rossi et al. used
CrOx/ZrO2, CrOx/ꢀ-Al2O3, and CrOx/SiO2,2 and Grzybowska
et al. also used CrOx/ꢀ-Al2O3.3
On the other hand, in the skeletal isomerization of butene,
the solid acidity of catalysts plays an important role. Gielgens
et al. have reported on the skeletal isomerization of 1-butene
over WO3/ꢀ-Al2O3 catalysts.4 Houzvicka et al. have studied
the skeletal isomerization of butene to isobutene over an
open-surface catalysts and several ZSM-5 samples, and found
that the weak acidity of catalysts (H3PO4/SiO2 and H-[Fe]-
ZSM-5) favored the high selectivity of isobutene.5 Seo et al.
have investigated reversible skeletal isomerization between bu-
tenes and isobutene, and found that FER, F/Al2O3, and KIT-1
showed a high selectivity of isobutene from butenes and bu-
tenes from isobutene.6
Cr/WO3–ZrO2 had the highest activity of dehydrogenation
and isomerization of butane to isobutene under both oxidative
and non-oxidative conditions. Kishida et al. investigated the di-
rect conversion of butane to isobutene over metal oxide cata-
lysts supported on ꢀ-alumina, and found that, of various kinds
of metal oxides, Ga(III) oxide catalyst alone could convert bu-
tane to isobutene; and doping of Cu(II) to the Ga(III) oxide cat-
alyst led to the highest yield of isobutene.9
Kishida et al. have also found Pt catalysts to be more effec-
tive for the direct conversion of butane to isobutene than
Ga(III) catalysts supported on corresponding zeolite-like mate-
rials, and that Pt catalyst supported on MFI-type silicoferra-
te(III) produced isobutene at the highest yield.10 On the other
hand, Byggningsbacka et al. have reported on the combination
of Zn-modified K-ZSM-5 with a ZSM-22 system for the simul-
taneous dehydrogenation and isomerization of butane to isobu-
tene.11 In their report, butene was obtained over a Zn-modified
K-ZSM-5 dehydrogenation catalyst, and isobutene was ob-
tained from butene over a ZSM-22 skeletal isomerization cata-
lyst. Pirngruber et al. studied the dehydrogenation and isomer-
ization of butane over Pt-ZSM-5 catalysts with a high Si/Al ra-
tio, and found that the highest yield of isobutene was approxi-
mately 12.5% at 830 K and 1.8 bar, and with a feed of 10%
butane and 20% hydrogen.12
However, when using these methods, two processes (dehy-
drogenation and skeletal isomerization) are still required to ob-
tain isobutene from butane, and, from the standpoint of energy
saving, the simultaneous dehydrogenation and isomerization of
butane to isobutene is highly desirable. Wang et al. have report-
ed on the simultaneous dehydrogenation and isomerization of
butane to isobutene over Cr-based ZrO2 catalysts under oxida-
tive conditions7 and Cr-based WO3-promoted catalysts under
non-oxidative conditions.8 In these studies, it was found that
On the other hand, zeolites have micropores with ordered
size and solid acidity and, as mentioned above, there has been
growing interest in applications of zeolites as catalysts as well
as molecular sieves. We have investigated the synthesis of nov-
el zeolites using ammonium salts as structure-directing agents
(SDAs).13,14 SSZ-35 has an unusual one-dimensional straight
channel structure with pore openings that alternate between
rings of ten tetrahedral atoms (10MR) and eighteen tetrahedral
Published on the web February 10, 2004; DOI 10.1246/bcsj.77.381

382 Bull. Chem. Soc. Jpn., 77, No. 2 (2004)
Dehydroisomerization of Butane over Cr Catalysts
night at room temperature. The ratios were as follows: Si/Al2 =
40, 100, 500, 1000, H2O/Si = 50, OHꢃ/Si = 0.1, SDA/Si =
0.2. Afterwards, the mixture was poured into Teflon-lined auto-
claves (Parr Instruments), and the sealed autoclaves were heated
at 170 ꢂC for 7 days. The obtained solid of Na-SSZ-35 was filtrat-
ed, washed with water and dried. Na-SSZ-35 was calcined at 550
ꢂC for 6 h in air, and converted to NH4-SSZ-35 by stirring over-
night in an ammonium nitrate solution, followed by filtration and
drying. The obtained NH4-SSZ-35 was calcined under the same
conditions as those mentioned above to produce H-SSZ-35.
An H-ZSM-12 support was hydrothermally synthesized with
hexamethylenebis(triethylammonium hydroxide) (Et3Nþ(CH2)6-
NþEt3 (OHꢃ)2) as SDA.14 Hexamethylenebis(triethylammonium
bromide) was prepared by refluxing 1,6-dibromohexane (Tokyo
Kasei) and triethylamine (Tokyo Kasei) in acetone. The precipitat-
ed bromide was filtered out, air-dried, and purified by recrystalliza-
tion using mixed solvents of ethanol and diethyl ether. The recrys-
tallized diammonium salt was air-dried after filtration, followed by
conversion to hydroxide using an ion-exchange resin. The solution
of hexamethylenebis(triethylammonium hydroxide) was mixed in
a Teflon-lined autoclave (Parr Instruments) with colloidal silica
(Shokubai Kasei, Cataloid), aluminum nitrate nonahydrate (Kanto
Chemical), NaOH (Nakarai Chemicals), and sulfuric acid to adjust
the total amount of OHꢃ. The ratios were as follows: Si/Al2 = 200,
1000, H2O/Si = 60, OHꢃ/Si = 0.2, Naþ/Si = 0.3, SDA/Si =
0.05. The as-synthesized crystals of Na-ZSM-12 were obtained
by heating in a sealed autoclave at 160 ꢂC for 4 days, followed
by cooling, washing with distilled water, filtrating, and drying.
atoms (18MR); and the micropore volume of this zeolite is larg-
er than those of other one-dimensional high-silica zeolites.
Wagner et al. reported the hydrothermal synthesis of SSZ-35,
in which cyclic and polycyclic quaternized amine molecules
were used as SDAs.15,16
In this study, referring to Wang’s reports,7,8 Cr catalysts
were prepared, and the conversion of butane over Cr catalysts
was investigated. Moreover, other kinds of metal catalysts were
prepared, and the catalytic activity of these catalysts for the
conversion of butane was compared with Cr catalysts. As a re-
sult, Cr catalysts supported on zeolites, especially H-SSZ-35
(Si/Al2 = 500), were found to be effective for this reaction,
and their effects on the conversion of butane and selectivity
of products were investigated.
Experimental
Synthesis of Zeolite Support. H-SSZ-35 support was hydro-
thermally synthesized using cis,cis,cis-N-methylhexahydrojuloli-
dinium hydroxide as SDA. The procedure for synthesizing the
SDA is shown in Fig. 1. cis,cis,cis-N-Methylhexahydrojulolidini-
um hydroxide was synthesized as follows: 2,6-bis(2-cyanoethyl)-
cyclohexanone was obtained from cyclohexanone (Wako Pure
Chemical) and acrylonitrile (Wako Pure Chemical) as the starting
materials, followed by cyclization under a high-pressure hydrogen
atmosphere (hydrogen pressure 10 MPa, temperature approx. 120
ꢂC) in an autoclave in the presence of a Raney nickel catalyst, to
produce hexahydrojulolidine.17 The obtained transparent hexahy-
drojulolidine oil was a mixture of cis,cis,cis-type (used as a precur-
sor of SDA), cis,trans,cis-type, and cis,cis,trans-type. To remove
the cis,trans,cis-type and cis,cis,trans-type, hexahydrojulolidine
oil was diluted with ether, refluxed with methyl iodide, and cooled.
After removing precipitated solids by filtration and evaporating the
residual solution, a cis,cis,cis-type transparent oil was obtained.
This oil was diluted with toluene and stirred at room temperature.
Methyl iodide was then added and the mixture refluxed. After cool-
ing, filtrating and drying, cis,cis,cis-N-methylhexahydrojulolidini-
um iodide, in the form of a white powder, was obtained. It was then
converted to hydroxide by ion-exchange resin.
ꢂ
Na-ZSM-12 was calcined at 500 C for 6 h in air, and converted
to NH4-ZSM-12 by stirring in a solution of ammonium nitrate
while heating for several days, followed by filtration and drying.
The obtained NH4-ZSM-12 was calcined under the same condi-
tions as above to finally obtain H-ZSM-12.
Other zeolite supports, such as USY (Ultra Stable Y zeolite),
H-Beta, H-ZSM-5, and H-mordenite, were obtained commercially
(Tosoh). Before use, these zeolites were also calcined at 500 ꢂC for
6 h in air.
Characterization of Zeolite Supports. To measure the solid
acidity of the supports, NH3-temperature-programmed-desorption
(TPD) experiments on zeolite supports were carried out on an
NH3-TPD apparatus (Ohkura Riken, Model ATD700A). TPD pro-
files were obtained under a vacuum at temperatures varying from
100 to 600 ꢂC at 10 ꢂC/min in the TPD process. Samples were de-
The solution of cis,cis,cis-N-methylhexahydrojulolidinium hy-
droxide was mixed with NaOH (Wako Pure Chemical), colloidal
silica (Shokubai Kasei, Cataloid), sodium aluminate (Wako Pure
Chemical), and distilled water in a glass beaker, and stirred over-
High-pressure H2
Raney Ni
CH2=CHCN
O
O
N
CN NC
(Mixture of cis,trans,cis-type, cis,cis,trans-type,
and cis,cis,cis-type)
H
H
H
CH3I
H
H
H
CH3I
Filtration
Ion exchange
Reflux
H
H
H
N
N
N
I
CH3
OH
CH3
(cis,cis,cis-type)
Fig. 1. Synthesis of cis,cis,cis-N-methylhexahydrojulolidinium hydroxide.

M. Inaba et al.
Bull. Chem. Soc. Jpn., 77, No. 2 (2004)
383
ꢂ
gassed at 500 C for 1 h under vacuum conditions before a mea-
surement. The surface area and micropore volume of the zeolite
supports ꢂwere measured by analyzing the adsorption of nitrogen
at ꢃ196 C using a volumetric apparatus (Nihon Bel, BELSORP
Table 1. Physico-Chemical Properties of H-SSZ-35
Si/Al2 Total surface area Micropore volume NH3 adsorption
m2 gꢃ1
ratio
mm3 gꢃ1
mmol gꢃ1
1010
844
ꢂ
28SA) after degassing at 300 C for 5.5 h under a vacuum.
40
100
500
390
484
486
172
214
222
Preparation of Cr Catalysts Supported on Zeolites. Cr cat-
alysts supported on zeolites were prepared by impregnation. As a
rule, the loading of Cr was 10 wt %, but in some cases the loading
was varied from 5 wt % to 20 wt %. Chromium(III) nitrate nona-
hydrate (Wako Pure Chemical) was used as the Cr source. After
294
8500
7500
6500
5500
4500
3500
2500
1500
500
ꢂ
impregnation, the wet catalysts were dried at 100 C in an oven,
followed by calcination at 700 ꢂC for 3 h in air. For a comparison,
a Cr catalyst supported on silica was prepared by the same method.
Characterization of Cr Catalysts Supported on Zeolites.
Powder X-ray diffraction analysis (Mac Science, M18XHF22-
SRA) of Cr-supported catalysts reduced in the flow of hydrogen
ꢂ
at 600 C was performed with Cu Kꢁ radiation, and the diameter
of Cr particles was calculated from the line width of XRD patterns.
Measurement of the Catalytic Activity. The catalytic activity
was measured using a fixed-bed reactor. The weight of the catalyst
was 1 g. Before the reaction, the catalyst was reduced at 600 ꢂC for
2 h in a flow of hydrogen. The effluent gas was analyzed by gas
chromatography (GC) with Molecular Sieve 5A and a Porapak Q
columns. Two detectors were used: TCD was used to detect hydro-
gen, and FID to detect hydrocarbons. The reactant gas contained n-
C4H10 (20%) and Ar (80%) and the gas flow rate was 60
cm3 minꢃ1. The reaction temperature was changed from 400 ꢂC
-500
100
200
300
400
500
600
Temperature / oC
Fig. 3. NH3-TPD profiles of H-SSZ-35 and other zeolites.
) H-SSZ-35 (Si/Al2 = 40), ( ) H-SSZ-35 (Si/Al2 =
to 600 C in 50 ꢂC steps.
ꢂ
(
100), ( ) H-SSZ-35 (Si/Al2 = 500), (þ) H-ZSM-5 (Si/
Results and Discussion
Al2 = 190), (ꢁ) H-mordenite (Si/Al2 = 240), ( ) H-Beta
ꢄ
(Si/Al2 = 27).
Characterization of the Zeolite Support and Cr Catalysts
Supported on Zeolites. The XRD pattern of SSZ-35 synthe-
sized in this study is shown in Fig. 2. This pattern is almost the
same as the pattern of SSZ-35 (International Zeolite Associa-
tion Code STF).15,16 The peaks at about 10ꢂ were weaker than
those of STF. No impurity peaks were observed.
showed two main NH3 desorption peaks: the desorption peak
at higher temperature was caused by solid acid. In the case of
H-SSZ-35 type zeolites, desorption peaks at higher tempera-
ꢂ
tures (about 300 C) were lower than those of other kinds of
zeolites, showing that the solid acidity of H-SSZ-35 type zeo-
lites is weaker than that seen in other kinds of zeolites.
An XRD measurement of Cr catalyst supported on zeolite
showed that Cr exists as Cr2O3 even after reduction in the flow
of hydrogen at 600 ꢂC. XRD peaks of Cr2O3 appeared at about
24.5, 33.5, 36.2, 41.5, 50.2, and 54.8ꢂ, and the size of Cr2O3
crystallites calculated from the XRD pattern at 54.8ꢂ was about
30 nm, much larger than the diameter of the zeolite micropores.
These results indicated that Cr2O3 particles were unable to en-
ter the zeolite micropores. There is a possibility that protons in
the framework of zeolites are exchanged with Cr cations; how-
ever, even if Cr cations exist, it appears that the quantity of Cr
cations is negligible, and they do not influence the catalytic ac-
tivity, since below 5 wt % of Cr-loading, the existence of Cr af-
fected the catalytic activity of Cr-supported catalysts (see
Fig. 6). Cr cations may be fully saturated even at low Cr-load-
ing, and do not increase by increasing Cr-loading. From this, it
seems that Cr cations do not act as catalytic active sites, but
Cr2O3 particles do.
Table 1 shows the results of the characterization of H-SSZ-
35 (Si/Al2 = 40, 100, 500). An investigation of these results
demonstrated that total surface area, and the micropore volume
increased with an increased Si/Al2 ratio, while the NH3 adsorp-
tion decreased with an increased ratio. As shown in Fig. 3,
where the NH3-TPD profile was measured, most zeolites
Catalytic Activity. Table 2 gives the conversion of butane,
the selectivity of each product, and the yield of isobutene over
zeolite supports alone and Cr catalysts supported on zeolites at
500 ꢂC. For a comparison, the conversion and selectivity over a
silica support and Cr catalysts supported on silica are also
shown in Table 2. In most cases, zeolite supports alone were
0
10
20
30
40
50
2θ / degree
Fig. 2. XRD pattern of SSZ-35 synthesized in this study.

384 Bull. Chem. Soc. Jpn., 77, No. 2 (2004)
Dehydroisomerization of Butane over Cr Catalysts
ꢂ
Table 2. Catalytic Performance of the Various Zeolite Catalysts at 500 C
Selectivity/C-%
Yield of
iso-C40
C-%
Conv.
Catalyst
Iso
1
Iso
2
1,3
C1{3
0
0
0
00
C-%
-C4
-C4
-C4
-C4
-C4
H-SSZ-35 (40)
Cr/H-SSZ-35 (40)
H-SSZ-35 (100)
Cr/H-SSZ-35 (100)
H-SSZ-35 (500)
Cr/H-SSZ-35 (500)
H-SSZ-35 (1000)
Cr/H-SSZ-35 (1000)
H-ZSM-12 (200)
Cr/H-ZSM-12 (200)
H-Beta (27)
Cr/H-Beta (27)
H-ZSM-5 (29)
Cr/H-ZSM-5 (29)
H-mordenite (18.3)
Cr/H-mordenite (18.3)
Cr/USY (360)
50.4
17.1
8.6
11.1
3.3
87.1
57.7
72.0
55.9
65.8
40.0
46.1
24.6
76.9
45.9
91.2
77.6
90.7
93.4
96.0
83.9
20.2
99.9
18.6
8.0
18.9
4.6
12.4
0.0
1.4
0.0
0.0
4.3
2.5
3.8
2.3
5.3
4.7
2.4
10.8
0.0
0.0
0.0
0.7
3.8
0.0
4.7
0.0
7.3
5.6
10.1
2.9
8.0
0.7
3.9
0.5
0.3
0.0
0.2
12.7
0.0
10.8
2.0
9.4
6.6
11.9
11.2
16.1
15.6
16.4
7.5
20.6
2.0
7.6
1.6
0.8
0.7
2.1
2.2
10.3
9.9
14.3
14.3
24.2
22.1
32.6
8.5
22.4
2.5
8.7
1.8
0.8
0.9
2.9
37.9
0.0
45.3
0.0
0.0
6.9
0.9
8.8
11.0
10.5
16.4
0.0
0.6
0.0
0.0
0.1
0.0
0.0
0.0
1.01
1.61
0.57
1.32
0.37
5.44
0.23
2.74
1.41
2.62
0.96
0.59
1.33
0.70
0.60
1.29
1.18
0.0
33.8
1.5
16.7
18.8
12.7
48.1
7.7
83.4
86.9
85.8
61.5
6.2
19.0
0.0
0.0
10.3
0.0
25.3
SiO2
Cr/SiO2
0.9
16.5
0.0
Number in parenthesis stands for Si/Al2 ratio.
found to be active in this reaction. The butane conversion was
in the order: H-mordenite (Si/Al2 = 18.3) > H-ZSM-5 (Si/Al2
= 29) > H-SSZ-35 (Si/Al2 = 40) > H-Beta (Si/Al2 = 27) >
H-ZSM-12 (Si/Al2 = 200) > H-SSZ-35 (Si/Al2 = 100) > H-
SSZ-35 (Si/Al2 = 500) > H-SSZ-35 (Si/Al2 = 1000). Howev-
er, these zeolite supports showed C1–C3 hydrocarbon forma-
tions to predominate over C4 products, and the selectivity of
C4 compounds such as isobutene was low. The loading of Cr
onto zeolite supports improved the selectivity of C4 com-
pounds. In particular, Cr catalysts supported on H-SSZ-35
(Si/Al2 = 100, 500, 1000) showed increased conversion as well
as the selectivity of isobutene. In the case of H-SSZ-35 (Si/Al2
= 500, 1000), the loading of Cr improved the yields of isobu-
tene (conversion of butane ꢁ selectivity of isobutene). Howev-
er, other catalyst systems showed improved isobutene selectiv-
ity and decreased butane conversion. On the other hand, in the
case of the Cr/H-ZSM-5 (Si/Al2 = 29) catalyst, the conversion
of butane increased somewhat, while the selectivity of isobu-
tene decreased.
Thus, zeolite catalysts were found to have catalytic activity
for the isomerization and dehydrogenation of butane into other
C4 compounds, such as isobutene. In most cases of zeolite sup-
ports, the selectivity of C4 compounds, especially isobutene,
was improved by the addition of Cr. In the case of H-SSZ-
35, an increased Si/Al2 ratio resulted in a decreased conversion
of butane and increased selectivity of dehydrogenated com-
pounds, such as isobutene. These indicated that there could
be a correlation between the solid acidity of the support and
the ability for dehydrogenation. The effect of Cr-loading on
the conversion of butane was dependent on the supports used;
however, the selectivity of dehydrogenated products was im-
proved by the addition of Cr.
dehydrogenated C4 products. However, no isomerized products
(isobutane and isobutene) were detected. These results suggest
that Cr2O3 promotes the dehydrogenation of butane, but does
not promote its isomerization;1–3 it also seems likely that skel-
etal isomerization takes place over the zeolite supports, and that
dehydrogenation occurs over both Cr2O3 particles and zeolite
supports.
Figure 4 shows the conversion of butane and the selectivity
of isobutene over Cr catalysts supported on zeolites at 500 ꢂC.
Here, the number next to each symbol stands for the Si/Al2 ra-
tio of the zeolite support. Cr/H-SSZ-35 (Si/Al2 = 500) showed
a moderate conversion of butane (33.8%) and selectivity of iso-
butene (16.1%); as a result, the yield of isobutene (conversion
of butane ꢁ selectivity of isobutene) was 5.44%, the highest
among the Cr-supported catalysts used in this study. It is char-
acteristic of H-SSZ-35 type zeolites that Cr catalysts supported
on zeolites with low Si/Al2 ratios (40, 100) show a lower con-
version of butane than most other kinds of zeolites, possibly at-
tributable to the weaker solid acidity of H-SSZ-35 than other
zeolite supports, which leads to a low rate of cracking of bu-
tane. Moreover, the micropore structure of the zeolite supports
affects the selectivity of isobutene, suggesting that H-SSZ-35
has a high shape-selectivity for the formation of isobutene.
As shown in Table 2, the selectivity of dehydrogenated C4
products (1-butene, isobutene, 2-butenes, and 1,3-butadiene)
ꢂ
over Cr/H-SSZ-35 (Si/Al2 = 500) at 500 C was 58.6%, and
the yield was 19.8%, the highest of the catalysts employed.
On the other hand, the selectivity of isomerized C4 products
(isobutane and isobutene) over Cr/H-SSZ-35 (Si/Al2 = 500)
was only 17.5%. These findings indicate that Cr/H-SSZ-35
(Si/Al2 = 500) has high activity for dehydrogenation and mod-
erate activity for the isomerization of butane.
On the other hand, SiO2 was almost inactive, while Cr/SiO2
showed a high conversion of butane and a high selectivity of
Figure 5 shows the conversion of butane and the selectivity
of each C4 product over Cr/H-SSZ-35 (Si/Al2 = 500) at each

M. Inaba et al.
Bull. Chem. Soc. Jpn., 77, No. 2 (2004)
385
30
1000
190
20
200
100
360
1000
500
240
10
0
40
27
18.3
60
29
0
20
40
80
100
Conversion of butane / %
Fig. 4. Conversion of butane and selectivity of isobutene
over Cr-supported catalysts (Cr = 10 wt %) at 500 ꢂC.
Fig. 6. Catalytic performance of the Cr/H-SSZ-35 (Si/Al2
= 500) catalyst as a function of Cr-loading at 500 ꢂC. Con-
version: (ꢁ) butane. Selectivity: ( ) C4 products, ( ) iso-
butane, ( ) 1-butene, ( ) isobutene, ( ) 2-butenes, (þ)
1,3-butadiene.
(
) Cr/H-SSZ-35, ( ) Cr/USY, ( ) Cr/H-ZSM-5, (
Cr/H-mordenite, ( ) Cr/H-Beta, (ꢁ) Cr/H-ZSM-12,
) Cr/SiO2. Number next to symbol stands for Si/Al2
)
(
ratio.
Fig. 7. Catalytic performance of the Cr/H-SSZ-35 (Cr = 10
wt %) catalyst as a function of Si/Al2 ratio at 500 ꢂC. Con-
version: (ꢁ) butane. Selectivity: ( ) C4 products, ( ) iso-
butane, ( ) 1-butene, ( ) isobutene, ( ) 2-butenes, (þ)
1,3-butadiene.
Fig. 5. Catalytic performance of the Cr/H-SSZ-35 (Si/Al2
= 500, Cr = 10 wt %) catalyst as a function of temperature.
Conversion: (ꢁ) butane. Selectivity: ( ) C4 products, (
)
isobutane, ( ) 1-butene, ( ) isobutene, ( ) 2-butenes, (þ)
1,3-butadiene.
perature, dehydrogenation predominates over skeletal isomeri-
zation.
temperature between 400 ꢂC and 600 ꢂC. The conversion of bu-
tane increased with increasing temperature (ꢁ), while the se-
lectivity of C4 products decreased ( ). These results suggest
that high temperature favors the cracking of butane over its de-
hydrogenation and isomerization. With increasing temperature,
the selectivity of 2-butenes gradually decreased, while the se-
lectivity of 1,3-butadiene increased. The selectivity of 1-butene
remained unchanged with temperature, but the selectivity of
The effect of Cr-loading is shown in Fig. 6. Below 10 wt %
of Cr-loading, the conversion of butane increased with increas-
ed Cr-loading, and leveled off beyond 10 wt % (ꢁ). On the oth-
er hand, the selectivity of C4 products, especially isobutene,
leveled off above 5 wt % of Cr-loading ( ). These results sug-
gest that the conversion of butane was affected by Cr-loading,
and that excessive loading of Cr did not always lead to a high
conversion of butane.
ꢂ
isobutene increased with temperatures below 500 C and de-
creased above 500 ꢂC. These findings suggest that at high tem-
The effect of the Si/Al2 ratio is shown in Fig. 7. As a result

386 Bull. Chem. Soc. Jpn., 77, No. 2 (2004)
Dehydroisomerization of Butane over Cr Catalysts
clear evidence that H-SSZ-35 type zeolite possesses the possi-
bility of use as a support for the production of isobutene by the
dehydrogenation and isomerization of butane.
Conclusions
Zeolites can catalyze the dehydrogenation and isomerization
of butane to isobutene. However, zeolite supports, especially
those having a low Si/Al2 ratio, favor the cracking of butane
over dehydrogenation and isomerization, due to their strong
solid acidity. The loading of Cr on zeolite supports enhances
the dehydrogenation and isomerization of butane. Of the Cr cat-
alysts supported on zeolites, Cr/H-SSZ-35 (Si/Al2 = 500)
showed moderate butane conversion and isobutene selectivity
and maintained its catalytic activity at 500 ꢂC for 6 h. As a re-
sult, the yield of isobutene (5.44%) was the highest among the
catalysts used in this study.
This work was supported by the Ministry of Economy, Trade
and Industry for the project on Molecular Harmonized Materi-
als.
Fig. 8. Catalytic performance of the Cr/H-SSZ-35 (Si/Al2
= 500, Cr = 10 wt %) catalyst as a function of time at
500 ꢂC. Conversion: (ꢁ) butane. Selectivity: ( ) C4 prod-
ucts, ( ) isobutane, ( ) 1-butene, ( ) isobutene, ( ) 2-
butenes, (þ) 1,3-butadiene.
References
1
45 (1999).
M. Hoang, J. F. Mathews, and K. C. Pratt, CHEMTECH, 9,
of increasing the Si/Al2 ratio, the selectivity of the total C4
products and dehydrogenated products (1-butene, isobutene,
2-butenes, and 1,3-butadiene) increased, while the selectivity
of isobutane decreased. On the other hand, the correlation be-
tween the Si/Al2 ratio and the conversion of butane was not
clear. It seems that solid acidity is needed for the isomerization
of butane, while an excess amount of solid acid leads to the
cracking of butane, rather than isomerization.
2 S. D. Rossi, M. P. Casaletto, G. Ferraris, A. Cimino, and G.
Minelli, Appl. Catal., A, 167, 257 (1998).
3
B. Crzybowska, J. Sloczynski, R. Grabowski, K. Wcislo, A.
Kozlowska, J. Stoch, and J. Zielinski, J. Catal., 178, 687 (1998).
L. H. Gielgens, M. G. H. van Kampen, M. M. Broek, R. van
Hardeveld, and V. Ponec, J. Catal., 154, 201 (1995).
J. Houzvicka, J. G. Nienhuis, and V. Ponec, Appl. Catal., A,
174, 207 (1998).
4
5
Wang et al. reported on the dehydrogenation and isomeriza-
tion of butane on Cr-supported WO3–ZrO2, but the catalytic ac-
tivity decreased with the reaction time as a result of carbon dep-
osition.7,8 As shown in Fig. 8, the C4 product selectivity over
Cr/H-SSZ-35 catalyst (Si/Al2 = 500) remained unchanged at
500 ꢂC for 6 h ( ), although butane conversion showed a slight
decrease (ꢁ).
6
(1998).
7
G. Seo, S. H. Park, and J. H. Kim, Catal. Today, 44, 215
S. Wang, K. Murata, T. Hayakawa, S. Hamakawa, and K.
Suzuki, Energy Fuels, 15, 384 (2001).
S. Wang, K. Murata, T. Hayakawa, S. Hamakawa, and K.
Suzuki, Catal. Lett., 66, 13 (2000).
Y. Takiyama, H. Nagata, M. Teshima, M. Kishida, H.
8
9
ꢀ
The diameter of 10MR of H-SSZ-35 was 5:5 ꢁ 6:1 A, and
Shimada, and K. Wakabayashi, Sekiyu Gakkaishi, 40, 199 (1997).
10 Y. Takiyama, H. Nagata, M. Kishida, and K. Wakabayashi,
Sekiyu Gakkaishi, 41, 80 (1998).
11 R. Byggningsbacka, N. Kumar, and L.-E. Lindfors, Catal.
Lett., 55, 173 (1998).
12 G. D. Pirngruber, K. Seshan, and J. A. Lercher, J. Catal.,
186, 188 (1999).
13 M. Inaba and H. Hamada, Stud. Surf. Sci. Catal., 125, 125
(1999).
ꢀ
that of 18MR was 12:5 ꢁ 9 A, much larger than the size of
the isobutene molecule. The other zeolites used (H-mordenite,
H-ZSM-5, H-Beta) also have micropores larger than the size of
isobutene molecules; however, they do not show a yield of iso-
butene higher than that from H-SSZ-35. This suggests that the
characteristic microstructure of H-SSZ-35 provides shape-
selectivity for butane conversion to isobutene. Moreover, H-
SSZ-35 type zeolites have a large micropore volume and weak-
er solid acidity than other kinds of zeolites in TPD. We believe
that these characteristics of H-SSZ-35 led to the highest isobu-
tene yield for butane conversion.
14 M. Inaba and H. Hamada, ZMPC 2000 (International
Symposium on Zeolites and Microporous Crystals), Sendai,
Abstracts, 1-P-034, p. 124 (2000).
The reaction path was postulated as follows: butane was de-
hydrogenated over a zeolite support or Cr2O3 particles, and a
part of the dehydrogenated products were skeletally isomerized
to isobutene over the zeolite support. The strong acidity of the
zeolite support favors the cracking of butane, and the loading of
Cr on zeolite improves the dehydrogenation, with the result that
the cracking of butane was suppressed.
15 P. Wagner, S. I. Zones, M. E. Davis, and R. C. Medrud,
Angew. Chem., Int. Ed., 38, 1269 (1999).
16 P. Wagner, Y. Nakagawa, G. S. Lee, M. E. Davis, S.
Elomari, R. C. Medrud, and S. I. Zones, J. Am. Chem. Soc., 122,
263 (2000).
17 L. Mandell, J. U. Piper, and K. P. Singh, J. Org. Chem., 28,
3440 (1963).
These findings on the catalytic activity and lifetime provide