Oxidative dehydrogenation of ethane with CO2 over Cr supported on submicron ZSM-5 zeolite

Article abstract of DOI:10.1016/S1872-2067(15)60893-2

A series of submicron ZSM-5-supported chromium oxide catalysts were prepared and characterized by XRD, N₂ adsorption, ²⁷Al MAS NMR, SEM, XPS, laser Raman spectroscopy and diffuse reflectance UV-Vis spectroscopy. The catalytic performance of these materials during ethane dehydrogenation in the presence of CO₂ was investigated. The catalysts exhibited both high activity and stability, with an ethane conversion of ～65% and ethylene yield of ～49% without any obvious deactivation following 50 h. Characterization results show that the excellent catalytic performance results from the high degree of dispersion of CrO_x species on the submicron ZSM-5 surface. Both a high Si/Al ratio and the use of the Na-form of the ZSM-5 support were found to favor CrO_x dispersion. The promotional effect of CO₂ on the dehydrogenation reaction was quite evident and can be attributed to the reverse water-gas shift reaction.

Full text of DOI:10.1016/S1872-2067(15)60893-2

Chinese Journal of Catalysis 36 (2015) 1242–1248
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c h n j c
Article
Oxidative dehydrogenation of ethane with CO
submicron ZSM-5 zeolite
2
over Cr supported on
a
a
a
b
a
a,
a
Yanhu Cheng , Fan Zhang , Yi Zhang , Changxi Miao , Weiming Hua , Yinghong Yue *, Zi Gao
a
Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, China
Shanghai Research Institute of Petrochemical Technology, SINOPEC, Shanghai 201208, China
b
A R T I C L E I N F O
A B S T R A C T
Article history:
A series of submicron ZSM-5-supported chromium oxide catalysts were prepared and characterized
Received 28 January 2015
Accepted 11 May 2015
Published 20 August 2015
by XRD, N
UV-Vis spectroscopy. The catalytic performance of these materials during ethane dehydrogenation
in the presence of CO was investigated. The catalysts exhibited both high activity and stability, with
2
adsorption, 27Al MAS NMR, SEM, XPS, laser Raman spectroscopy and diffuse reflectance
2
an ethane conversion of 65% and ethylene yield of 49% without any obvious deactivation fol-
lowing 50 h. Characterization results show that the excellent catalytic performance results from the
Keywords:
Dehydrogenation
Ethane
ZSM-5 zeolite
Submicron
Carbon dioxide
high degree of dispersion of CrO
and the use of the Na-form of the ZSM-5 support were found to favor CrO
tional effect of CO on the dehydrogenation reaction was quite evident and can be attributed to the
reverse water-gas shift reaction.
2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
x
species on the submicron ZSM-5 surface. Both a high Si/Al ratio
x
dispersion. The promo-
2
©
1.
Introduction
[1–4] and CO
The dehydrogenation of ethane over In [5], Cr [6,7], Ga [8,9],
Co [10] and Mn [11]-containing catalysts in the presence of CO
2
[5–11].
The catalytic conversion of light alkanes such as ethane and
2
propane into the corresponding value-added alkenes has
gained much attention over the past several decades because of
the growing demand for light alkenes. The dehydrogenation of
alkanes is endothermic and is inevitably controlled by the
thermodynamic equilibrium, thus relatively high temperatures
are required to obtain high yield of alkenes, resulting in high
energy consumption and ready deactivation of the catalyst. For
this reason, oxidative dehydrogenation using oxygen has been
proposed as an alternative process. However, the over-oxida-
tion of alkanes to carbon dioxide is unavoidable during this
process, leading to a decrease in the targeted product selectivi-
ty. However, it has been reported that these disadvantages can
has been studied intensely for some time now. Cr-based cata-
lysts in particular show excellent activity for the dehydrogena-
tion of ethane, and CO
leading to a significant increase in ethylene yield in the pres-
ence of CO over Cr-based catalysts. Because of the low surface
area of bulk crystalline chromium oxides, Cr species are often
dispersed on supports with high surface areas, such as Al
[7], SiO [7], ZrO [12,13], TS-1 [14], mesoporous silicas like
2
can markedly promote the reaction,
2
O
2 3
2
2
SBA-1 [15], SBA-15 [16], MSU-x [17], MCM-41 [18] and oxi-
dized diamond [19,20], so as to prepare a catalyst with an
abundance of active sites.
ZSM-5 plays a very important role both in industrial pro-
cesses and in academic studies as either a catalyst or a catalyst
be overcome by replacing O
2
with milder oxidants, such as N O
2
*
Corresponding author. Tel: +86-21-65642409; Fax: +86-21-65641740; E-mail: yhyue@fudan.edu.cn
This work was supported by the National Natural Science Foundation of China (20773027, 20773028 and 21273043) and the Science & Technology
Commission of Shanghai Municipality (08DZ2270500).
DOI: 10.1016/S1872-2067(15)60893-2 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 8, August 2015

Yanhu Cheng et al. / Chinese Journal of Catalysis 36 (2015) 1242–1248
1243
support, owing to its three-dimensional microporous structure,
catalysts were determined by N
2
adsorption at –196 °C using a
high surface area and high thermal and hydrothermal stability.
ZSM-5-supported metal oxide catalysts have been investigated
Micromeritics ASAP 2000 instrument. Scanning electron mi-
croscopy (SEM) images were recorded digitally on a Philips XL
30 microscope operating at 30 kV. Laser Raman spectra were
obtained with a Horiba JY XPloRA spectrometer using the 532
nm radiation from an air-cooled solid state laser as the excita-
tion source. The other parameters included a laser power of 25
mW, a data acquisition time of 30 s, an accumulation number of
8 and a spectral resolution of 2 cm . The spectra were ob-
tained at room temperature under ambient conditions. DRS
spectra were collected on a Shimadzu UV-2450 spectrometer
equipped with an integrating sphere attachment. XPS data
were acquired using a Perkin-Elmer PHI 5000C spectrometer
with regard to ethane or propane dehydrogenation using CO ,
2
and H-form ZSM-5 with a Si/Al ratio over 1900 has been re-
ported to be preferred as the support [21]. More recently, Cr
supported on Na-type ZSM-5 having a smaller crystal size (ca.
4
00 nm) was found to be more effective when applied to the
dehydrogenation of propane in the presence of CO , although
the stability of the catalyst system was still not satisfactory
22].
In our present work, a series of Cr catalysts supported on
–1
2
[
submicron H- or Na-form ZSM-5 materials having various Si/Al
ratios were prepared and characterized by X-ray diffraction

with Mg K radiation as the excitation source. All binding ener-
(
XRD), nitrogen adsorption, laser Raman spectroscopy, X-ray
gy values were referenced to the C 1s peak at 284.6 eV.
TPR profiles were obtained on a Micromeritics AutoChem II
apparatus loaded with 100 mg of catalyst. The TPR experi-
photoelectron spectroscopy (XPS), diffuse reflectance UV-Vis
spectroscopy (DRS) and temperature-programmed reduction
(
TPR). The catalytic performance of each of these submicron
ZSM-5-supported Cr-based catalysts during the dehydrogena-
tion of ethane to ethylene in the presence of CO
was also in-
ments were carried out in a 30 mL/min flow of 10% H
2
-90% Ar
with a ramp rate of 10°C/min. H consumption was monitored
2
2
using a thermal conductivity detector. Thermogravimetric (TG)
analysis was performed under an air flow on a Perkin-Elmer 7
Series Thermal Analyzer to determine the amount of coke de-
posited on the catalyst following the reaction.
vestigated. The relationship between catalytic behavior and
physicochemical properties is discussed herein on the basis of
the experimental results.
2
.
Experimental
.1. Catalyst preparation
Submicron ZSM-5 zeolite was prepared using procedures
2.3. Catalytic testing
2
Catalytic tests for ethane dehydrogenation with CO were
2
performed at 650 °C in a fixed-bed flow microreactor at at-
mospheric pressure. The catalyst load was 200 mg, and each
sample was pretreated at 650 °C for 2 h under a nitrogen flow
prior to the reaction. The gaseous reactant contained 3%
previously reported in the literature [23], employing
tetrapropylammonium hydroxide (TPAOH, 25% aqueous solu-
tion, Yixing Dahua) as the template. Typically, NaAlO
2
(CP, Si-
ethane and 15% CO with the balance consisting of nitrogen at
2
nopharm Chemical) was dissolved in an aqueous TPAOH solu-
tion, after which tetraethylorthosilicate (TEOS, AR, Shanghai
Lingfeng) was added. The resulting mixture was stirred for 6 h
at room temperature, followed by heating at 50°C with further
stirring to evaporate the ethanol resulting from the reaction. A
clear gel was obtained with the molar composition
a total flow rate of 30 mL/min. The hydrocarbon reaction
products were analyzed using an on-line gas chromatograph
(GC) equipped with a 6 m Porapak Q packed column and a
flame ionization detector (FID). The gaseous products were
analyzed on-line using a second GC equipped with a thermal
conductivity detector (TCD) and a carbon molecular sieve 601
column. The reverse water-gas shift reaction was performed in
a fixed-bed flow microreactor at atmospheric pressure using a
1
20SiO
2
:xAl
2
O
3
:48TPAOH:3600H O. This gel was transferred to
2
an autoclave and crystallized by heating at 170°C for 2 d. The
obtained product was centrifuged, washed, dried at 110 °C
overnight and then calcined in air at 600 °C for 6 h to remove
the template.
catalyst load of 200 mg. The H
2
:CO
2
:N molar ratio was 1:1:1,
2
and the total flow rate of the gaseous reactants was 30 mL/min.
The reaction temperature was in the range of 500–650 °C. The
The supported chromium oxide catalysts were prepared by
impregnating ZSM-5 with an aqueous solution of
amounts of CO before and after the reaction were determined
2
by on-line analysis with a GC equipped with a carbon molecular
sieve 601 column and a TCD. The reaction data in this work
were reproducible, with a variation of less than 5%.
Cr(NO
wetness method. The impregnated samples were dried at 110
C overnight and calcined in air at 650°C for 6 h. The obtained
catalysts are denoted as yCr/ZSM-5-c, where y represents the
3 3 2
) 9H O (AR, Sinopharm Chemical) using the incipient
°
3. Results and discussion
mass fraction of Cr
2
O in the catalysts, and c represents the
3
Si/Al ratio in gel.
3.1. Structural Characterization
2
.2. Catalyst characterization
Figure 1 shows the XRD patterns of the various ZSM-5-sup-
ported chromium oxide catalysts. All exhibit well-crystallized
MFI structures with characteristic reflections at 2θ = 8.0°, 8.9°,
23.1°, 23.4° and 24.0° [24]. No diffraction patterns corre-
sponding to chromium oxide were observed, suggesting that
XRD patterns were acquired with a Persee XD-2 X-ray dif-
fractometer using nickel-filtered Cu K radiation at 40 kV and
0 mA. The BET surface areas and micropore volumes of the

3

1244
Yanhu Cheng et al. / Chinese Journal of Catalysis 36 (2015) 1242–1248
Table 1
Textural properties of supported chromium oxide catalysts.
Surface
External
Pore
Micropore
(4)
a
a
Catalyst
area
surface area
volume
volume
2
2
3
3
(
m /g)
(m /g)
(cm /g)
(cm /g)
(
3)
3Cr/NaZSM-5-60
339
308
356
342
53
38
34
36
0.27
0.21
0.24
0.24
0.17
0.14
0.16
0.15
3
3
Cr/NaZSM-5-100
Cr/NaZSM-5-160
Cr/HZSM-5-160
(2)
3
a
Calculated by the t-plot method.
(1)
(
3)
1
0
20
30
40
50
o
2
/( )
Fig. 1. XRD patterns of (1) 3Cr/NaZSM-5-60, (2) 3Cr/NaZSM-5-100, (3)
Cr/NaZSM-5-160 and (4) 3Cr/HZSM-5-160.
(2)
3
the chromium oxide was well dispersed on all the ZSM-5 sup-
ports.
(1)
SEM images of the ZSM-5 supports are presented in Fig. 2.
All samples were well crystallized without any presence of
amorphous materials and exhibit a rod-like morphology with a
uniform crystallite size distribution. The average crystallite size
was approximately 400 nm for all the ZSM-5 zeolites.
The textural properties of the ZSM-5-supported chromium
oxide catalysts are summarized in Table 1. These catalysts,
regardless of whether the ZSM-5 support was the Na- or
H-form or had a low or high Si/Al ratio, exhibit similar BET
surface areas and micropore volumes, showing that the sup-
ports had similar crystallinities and that their micropore chan-
-
200
-100
0
100
200
Chemical shift
Fig. 3. 27Al MAS NMR spectra of (1) ZSM-5-60, (2) ZSM-5-100 and (3)
ZSM-5-160.
Table 2
XPS and TPR data for supported chromium oxide catalysts.
Cr6+/Cr3+
b
BE (eV)
Cr3+
Cr6+ atomic ratio
576.5 579.5
H
2
consumption
(mmol/g)
0.24
Catalyst
a
3
3
3
3
a
Cr/NaZSM-5-60
Cr/NaZSM-5-100 576.5 579.5
Cr/NaZSM-5-160 576.5 579.5
Cr/HZSM-5-160
Calculated from XPS peak areas.
Obtained by TPR.
2.87
1.82
0.92
0.89
0.35
0.36
0.32
nels were not blocked by the supported CrO
species.
x
576.5 579.5
27Al MAS NMR spectra of the ZSM-5 supports were acquired
to characterize the local coordination environment of the alu-
minum atoms in the zeolites. An intense line at δ = 55, assigned
to ZSM-5 framework aluminum atoms in tetrahedral coordina-
tion, can be observed in the spectra of all the samples, while no
discernable signal at δ = 0, attributed to extra-framework alu-
minum atoms in octahedral coordination, is evident (Fig. 3).
The absence of extra-framework aluminum atoms indicates
that all of the Al species have been incorporated into the zeolite
framework.
b
eV, assigned to Cr3+ and Cr , respectively [22,25,26], and the
quantitative data after fitting are listed in Table 2. All the cata-
lysts were found to have similar binding energy (BE) values.
The Cr /Cr ratio evidently decreases with increasing Si/Al
ratios and as the Na content is decreased, indicating that Na+
cations may have a positive effect in terms of raising the
Cr /Cr ratio, similar to the action of K ions in K-doped
CrO /Al catalysts [27]. Compared with the NaZSM-5-sup-
ported catalyst, the HZSM-5 material having the same Si/Al
ratio exhibited a lower Cr /Cr ratio, which may also result
from a lower Na content.
6+
6+
3+
6
+
3+
+
x
O
2 3
3.2. State of Cr species
6
+
3+
XPS was employed to investigate the oxidation states of Cr
species. The Cr 2p2/3 spectra obtained from the catalysts were
deconvoluted into two bands at approximately 576.5 and 579.5
Additional information on the state of Cr species was ob-
tained from UV-Vis diffuse reflectance measurements, and the
(a)
(b)
(c)
Fig. 2. SEM images of (a) ZSM-5-60, (b) ZSM-5-100 and (c) ZSM-5-160.

Yanhu Cheng et al. / Chinese Journal of Catalysis 36 (2015) 1242–1248
1245
272
370
468
605
(4)
(
4)
3)
(3)
(2)
(1)
(
(
2)
1)
(
2
00
300
400
Wavelength (nm)
Fig. 4. Diffuse reflectance UV-Vis spectra of (1) 3Cr/NaZSM-5-60, (2)
Cr/NaZSM-5-100, (3) 3Cr/NaZSM-5-160 and (4) 3Cr/HZSM-5-160.
500
600
700
100
200
300
400
500
600
700
800
o
Temperature ( C)
2
Fig. 6. H -TPR profiles of (1) 3Cr/NaZSM-50, (2) 3Cr/NaZSM-5-100, (3)
3
3Cr/NaZSM-5-160 and (4) 3Cr/HZSM-5-160.
–
1
results are summarized in Fig. 4. Two bands are observed for
each catalyst, at approximately 272 and 370 nm, assigned to
the O →Cr charge transfer transition of chromate species in
810 cm , attributed to the bending mode of the Cr–O–Cr link-
age of polymeric chromates, also appears. The intensity of the
band at 1000 cm–1 increases as the Si/Al ratio is increased, in-
dicating that the dispersed Cr(VI) species on the catalyst sur-
faces gradually transition from monochromates to polymeric
chromates with increasing Si/Al ratios.
2–
6+
tetrahedral coordination [25,28–32]. Bands at 468 and 605 nm,
corresponding to octahedral Cr3+ species in Cr
O
or CrO clus-
2
3
x
ters, are not present, indicating that all Cr species were well
dispersed on the submicron ZSM-5 support.
H -TPR was carried out to characterize the redox ability of
2
Laser Raman spectra were acquired to identify the molecu-
lar nature of the Cr species dispersed on the ZSM-5 supports,
Cr species on the catalysts, which has a very important effect on
the dehydrogenation activity. The results are presented in Fig.
6 and Table 2. It is evident that there is only one reduction peak
–1
and the results are depicted in Fig. 5. A band at 551 cm , as-
signed to crystalline Cr , appears in the spectra of the
Cr/HZSM-5-160 catalyst [18,22,25,30–33], while the band at
O
2 3
at 370 °C, with a shoulder at 270 °C, that can be attributed to
the reduction of Cr6+ to Cr3+ (and/or Cr ) [30–32]. H
2+
con-
3
2
the same position is much weaker in the case of the NaZSM-5
supported catalysts. The intensity of the 551 cm–1 band de-
creases in the order 3Cr/HZSM-5-160 > 3Cr/NaZSM-5-60 >
sumption is higher over the NaZSM-5-supported catalysts as
compared with HZSM-5 material, and increases as the Si/Al
ratio is increased, indicating increasing quantities of reducible
surface Cr . All these findings are consistent with the data ob-
tained from laser Raman studies, showing that high Si/Al ratios
6+
3
Cr/NaZSM-5-100  3Cr/NaZSM-5-160. These results demon-
strate that the use of a high Si/Al ratio and the Na-form of the
zeolite favor CrO dispersion.
x
and the Na-form are favorable for CrO dispersion.
x
Two intense bands at approximately 980 and 1000 cm–1 are
present in the spectrum of each of the catalysts, and can be
ascribed to the symmetric vibrational modes of the terminal
Cr=O bonds of monochromates and polymeric chromates, re-
spectively [18,22,25,30–33]. Meanwhile, a weak, broad band at
3.3. Catalytic activity
The prepared Cr/ZSM-5 catalysts were evaluated during
ethane dehydrogenation in the presence of CO , and the results
2
are shown in Table 3. For each catalyst, the ethane conversion
drops with reaction time while the selectivity for ethylene in-
creases. There are only minimal differences in the initial activi-
ties as well as the initial ethylene yields among the Cr/NaZSM-5
catalysts, although the stability is improved with increasing
Si/Al ratios in the ZSM-5 support, resulting in a slight increase
in the plateau value for the yield of ethylene. While all the sub-
micron particle-supported catalysts exhibit superior perfor-
mance, the 3Cr/NaZSM-5-160 shows higher activity than the
(
4)
3)
(
(
2)
1)
3Cr/HZSM-5-160.
Cr-based catalysts have been reported to represent one of
the most promising catalysts for light alkane dehydrogenation
reactions because of their high catalytic efficiency both in the
(
absence and presence of CO
. There are two types of coordina-
2
5
00
600
700
800
Raman shift (cm )
Fig. 5. Laser Raman spectra of (1) 3Cr/NaZSM-5-60, (2)
Cr/NaZSM-5-100, (3) 3Cr/NaZSM-5-160 and (4) 3Cr/HZSM-5-160.
900 1000 1100 1200

tively-unsaturated Cr(III) in chromium species, Cr(III) ions
formed from the reduction of Cr(VI) and dispersed on fresh
catalysts. Both are generally considered as active sites during
3

1246
Yanhu Cheng et al. / Chinese Journal of Catalysis 36 (2015) 1242–1248
Table 3
Reaction data for ZSM-5-supported chromium oxide catalysts obtained at 10 min and 6 h.
Selectivity (%)
Conversion (%)
Yield (%)
Catalyst
CH
4
C H
2 4
C H
3 6
1
0 min
64.1
65.9
65.5
59.1
6 h
10 min
24.1
25.6
24.3
26.3
6 h
10 min
6 h
10 min
6 h
0.2
0.1
0.2
0.3
10 min
6 h
3Cr/NaZSM-5-60
3Cr/NaZSM-5-100
3Cr/NaZSM-5-160
3Cr/HZSM-5-160
57.9
60.5
61.3
57.2
18.0
19.9
20.9
23.2
75.7
74.2
75.4
73.4
81.8
79.9
78.9
76.2
0.2
0.1
0.3
0.3
48.5
48.9
49.4
43.4
47.4
48.3
48.4
43.7
non-oxidative dehydrogenation and oxidative dehydrogenation
reaction processes. However, several groups have reported
that coordinatively unsaturated Cr(III) formed from the reduc-
tion of higher-valence states (i.e. Cr(VI)) is more active, wheth-
er applied to the non-oxidative dehydrogenation reaction or
9
8
7
6
5
4
0
0
0
0
0
0
(2)
oxidative dehydrogenation with CO
reducible Cr(VI) on the calcined samples is crucial for the de-
hydrogenation reaction [17,32]. H consumption results allow
2
. As a result, the amount of
2
(1)
one to estimate the amount of redox-active Cr(VI) species, and
it can be seen from Table 2 that the amount of reducible Cr(VI)
on the freshly calcined samples increases with the Si/Al ratio,
which is in agreement with their increasing dehydrogenation
activity. These results confirm that the reducible Cr(VI) makes
an important contribution to the dehydrogenation reaction.
This is also the reason why the activity of the 3Cr/NaZSM-5 is
higher than that of the 3Cr/HZSM-5.
(3)
0
10
20
30
40
50
Time on stream (h)
Fig. 7. (1) Ethane conversion, (2) ethylene selectivity and (3) ethylene
yield over 3Cr/NaZSM-5-160 as functions of reaction time.
The type of Cr(VI) species is considered to be another pos-
sible factor in the dehydrogenation reaction. Kumar et al. [34]
reported that isolated chromium species are more active for
although the activity does drop slowly. This is quite different
from the behavior of other commonly studied Cr-containing
catalysts, over which the ethylene yields are reported to have
dropped quickly within 6 h.
the dehydrogenation reaction than crystalline α-Cr
2
O , whereas
3
oligomeric chromium species are more active than isolated
chromium species. We can see from Fig. 5 that dispersed Cr(VI)
species are present in the form of polymeric chromates and
monochromates on the surface of Cr/NaZSM-5 while crystal-
3.4. Effect of CO
2
partial pressure
partial pressure on the dehydrogenation of
line Cr O
2 3
was formed on the Cr/HZSM-5. This may be the rea-
The effect of CO
ethane was also investigated, and the results are summarized
in Table 4. The promotional effect of CO on the reaction is
quite evident. The initial ethane conversion increases quickly
from 20.4% with increasing CO /C ratios until it reaches its
peak at 65.5% when the CO /C ratio equals 5, after which
the conversion decreases slightly with further increases in the
CO /C ratio. The effect of CO can be attributed to the re-
verse water-gas shift reaction, which accelerates the formation
of the dehydrogenation products by transforming H and CO
into CO and H O. This is demonstrated by the results of the
/CO reaction over 3Cr/NaZSM-5-160. Obviously, the cata-
lyst is very active for the reverse water-gas shift reaction, with
a CO conversion of 22.6% at 650°C.
2
son why 3Cr/HZSM-5-160 exhibits relatively low activity even
though it has a higher amount of reducible Cr(VI) as compared
with 3Cr/NaZSM-5-60.
The effect of the Cr loading on the dehydrogenation activity
was also investigated. The ethane conversion was found to
increase with increasing extents of Cr loading and then de-
creased as the Cr content was further increased, such that mass
2
2
H
2 6
2
H
2 6
2
H
2 6
2
fraction of 3% Cr
2
O is optimal.
3
To investigate the stability of the 3Cr/NaZSM-5-160 cata-
lyst, the dehydrogenation reaction was run continuously for 50
h, with the results shown in Fig. 7. The catalyst is relatively
stable; the ethylene yield over the catalyst is maintained at
about 46% without any obvious deactivation over the 50 h,
2
2
2
H
2
2
2
Table 4
Reaction data for 3Cr/NaZSM-5-160 under different CO
2
partial pressures obtained at 10 min and 6 h.
Selectivity (%)
Conversion (%)
Yield (%)
10 min
C
2
H
6
/CO
2
ratio
CH
4
C H
2 4
C
H
3 6
1
0 min
20.4
55.2
60.5
65.5
64.9
6 h
10 min
3.1
15.4
18.7
24.3
23.7
6 h
2.4
14.2
17.3
20.9
20.3
10 min
95.6
84.3
81.1
75.4
6 h
10 min
6 h
0.8
0.3
0.2
0.2
0.2
6 h
∞
12.5
52.6
57.8
61.3
60.3
96.8
85.5
82.5
78.9
79.5
1.3
0.3
0.2
0.3
0.2
19.5
46.5
49.1
49.4
49.4
12.1
45.0
47.7
48.4
48.0
1/1
1/3
1/5
1/7
76.2

Yanhu Cheng et al. / Chinese Journal of Catalysis 36 (2015) 1242–1248
1247
The stability of the catalysts was also improved greatly by
the addition of CO . About 40% of the initial activity was lost
within 6 h in the absence of CO . However, when 15% CO was
role in the ethane dehydrogenation reaction. The type of Cr(VI)
species present is another possible factor affecting the dehy-
drogenation reaction.
2
2
2
introduced, only 5% loss was observed during the same period.
The enhanced stability can be explained primarily by two ef-
References
6+
3+
fects: (1) CO
dation of reduced Cr species, Cr(III)Ox–1 + CO
and regenerates the active species [6,7,17,35–37], and (2) CO
eliminates the formation of coke by the Boudouard reaction,
CO + C → 2CO, and thus exposes more active sites to the reac-
2
promotes the Cr /Cr reaction through the oxi-
2
→ Cr(VI)O + CO,
x
[1] Sazama P, Sathu N K, Tabor E, Wichterlová B, Sklenák Š, Sobalík Z.
J Catal, 2013, 299: 188
2
[2] Kowalska-Kus J, Held A, Nowinska K. Catal Lett, 2010, 136: 199
[3] Wu G J, Fei H, Guan N J, Li L D. Catal Sci Technol, 2013, 3: 1333
[4] Koekkoek A J J, Kim W, Degirmenci V, Xin H, Ryoo R, Hensen E J M.
J Catal, 2013, 299: 81
2
tants [6,7,17,35–37]. This can be confirmed by thermogravi-
metric tests that show that the amount of coke deposited on the
[5] Chen M, Wu J L, Liu Y M, Cao Y, Guo L, He H Y, Fan K N. Appl Catal
catalyst after 6 h is 3.4% in the absence of CO
higher than the 3.0% amount obtained in the presence of CO
The fact that the Boudouard reaction proceeds is also evident
from the observation that the molar ratio of CO formed to CO
2
, a value that is
A, 2011, 407: 20
2
.
[
6] Wang S B, Zhu Z H. Energ Fuels, 2004, 18: 1126
7] Wang S B, Murata K, Hayakawa T, Hamakawa S, Suzuki K. Appl
Catal A, 2000, 196: 1
[
2
converted is approximately 1.4 during the reaction, since this
ratio should be equal to unity if the Boudouard reaction does
not occur.
[8] Nakagawa K, Okamura M, Ikenaga N, Suzuki T, Kobayashi T. Chem
Commun, 1998: 1025
[9] Shen Z H, Liu J, Xu H L, Yue Y H, Hua W M, Shen W. Appl Catal A,
2009, 356: 148
[
10] Zhang X, Ye Q, Xu B Q, He D H. Catal Lett, 2007, 117: 140
11] Jin L, Reutenauer J, Opembe N, Lai M, Martenak D J, Han S, Suib S L.
ChemCatChem, 2009, 1: 441
4
.
Conclusions
[
Catalysts composed of submicron ZSM-5-supported chro-
[
[
[
[
12] Deng S, Li H Q, Li S G, Zhang Y. J Mol Catal A, 2007, 268: 169
13] Deng S, Li S G, Li H Q, Zhang Y. Ind Eng Chem Res, 2009, 48: 7561
14] Zhao X H, Wang X L. Catal Commun, 2006, 7: 633
mium oxide particles were prepared by an incipient wetness
method, and their catalytic performance for ethane dehydro-
genation in the presence of CO was compared. The results
show that chromium oxide supported on submicron Na-type
ZSM-5 with a high Si/Al ratio is an excellent catalyst for the
oxidative dehydrogenation of ethane with CO
well as high stability can be obtained over this catalyst. The
promotional effect of CO on dehydrogenation can also be ob-
2
15] Michorczyk P, Ogonowski J, Niemczyk M. Appl Catal A, 2010, 374:
142
[
[
[
16] Shi X J, Ji S F, Wang K. Catal Lett, 2008, 125: 331
2
. High activity as
17] Baek J, Yun H J, Yun D, Choi Y, Yi J. ACS Catal, 2012, 2: 1893
18] Wang Y, Ohishi Y, Shishido T, Zhang Q H, Yang W, Guo Q, Wan H L,
Takehira K. J Catal, 2003, 220: 347
2
served on this catalyst and is attributed to the reverse wa-
ter-gas shift reaction. Characterization by laser Raman, UV-Vis
[
19] Nakagawa K, Kajita C, Ikenaga N O, Suzuki T, Kobayashi T,
Nishitani-Gamo M, Ando T. J Phys Chem B, 2003, 107: 4048
DRS, XPS and H
species can be achieved in submicron catalysts, resulting in a
greater quantity of the reducible Cr(VI) species that play a key
2
-TPR revealed that improved dispersion of Cr
[20] Nakagawa K, Kajita C, Ikenaga N O, Nishitani-Gamo M, Ando T,
Suzuki T. Catal Today, 2003, 84: 149
[21] Mimura N, Okamoto M, Yamashita H, Oyama S T, Murata K. J Phys
Graphical Abstract
Chin. J. Catal., 2015, 36: 1242–1248 doi: 10.1016/S1872-2067(15)60893-2
Oxidative dehydrogenation of ethane with CO over Cr supported on submicron ZSM-5 zeolite
2
Yanhu Cheng, Fan Zhang, Yi Zhang, Changxi Miao, Weiming Hua, Yinghong Yue *, Zi Gao
Fudan University; Shanghai Research Institute of Petrochemical Technology, SINOPEC
1
00
C H
2
6
C
2
H
4
selectivity
conversion
8
6
4
2
0
0
0
0
0
Cr
O
2 6
C H
2 4
C H yield
0
10
20
30
40
50
Submicron ZSM-5 Zeolite
C H
2 4
Time on stream (h)
Submicron ZSM-5 supported chromium oxide catalysts were prepared and exhibit both high activity and stability, with an ethane conver-
sion of 65% and ethylene yield of 49% without any obvious trend of deactivation in 50 h.

1248
Yanhu Cheng et al. / Chinese Journal of Catalysis 36 (2015) 1242–1248
Chem B, 2006, 110: 21764
Santucci A, Del Piero G. J Catal, 1996, 158: 236
[30] Rao T V M, Deo G, Jehng J M, Wachs I E. Langmuir, 2004, 20: 7159
[31] Weckhuysen B M, Wachs I E, Schoonheydt R A. Chem Rev, 1996,
96: 3327
[32] Puurunen R L, Weckhuysen B M. J Catal, 2002, 210: 418
[33] Weckhuysen B M, Jehng J M, Wachs I E. J Phys Chem B, 2000, 104:
7382
[
[
[
[
[
[
22] Zhang F, Wu R X, Yue Y H, Yang W M, Gu S Y, Miao C X, Hua W M,
Gao Z. Microporous Mesoporous Mater, 2011, 145: 194
23] Wang Y, Guo L F, Ling Y, Liu Y M, Li X H, Wu H H, Wu P. Appl Catal
A, 2010, 379: 45
24] Sang S Y, Chang F X, Liu Z M, He C Q, He Y L, Xu L. Catal Today,
2004, 93-95: 729
25] Ayari F, Mhamdi M, Álvarez-Rodríguez J, Ruiz A R G, Delahay G,
Ghorbel A. Appl Catal B, 2013, 134-135: 367
26] Kytokivi A, Jacobs J P, Hakuli A, Merilainen J, Brongersma H H. J
Catal, 1996, 162: 190
27] Rombi E, Cutrufello M G, Solinas V, De Rossi S, Ferraris G, Pistone
A. Appl Catal A, 2003, 251: 255
[34] Kumar M S, Hammer N, Rönning M, Holmen A, Chen D, Walmsley J
C, Öye G. J Catal, 2009, 261: 116
[35] Mimura N, Takahara I, Inaba M, Okamoto M, Murata K. Catal
Commun, 2002, 3: 257
[36] Shishido T, Shimamura K, Teramura K, Tanaka T. Catal Today,
2012, 185: 151
[
28] Michorczyk P, Ogonowski J, Zenczak K. J Mol Catal A, 2011, 349: 1
29] Cavani F, Koutyrev M, Trifiro F, Bartolini A, Ghisletti D, Iezzi R,
[37] Nakagawa K, Kajita C, Ikenaga N, Nishitani-Gamo M, Ando T,
Suzuki T. Catal Today, 2003, 84: 149
[