Effect of granulation on Co-Al2O3 aerogel catalyst activity & stability

Cite this: RSC Advances, 2013, 3,
8939
Effect of granulation on the activity and stability of a
Co–Al2O3 aerogel catalyst in a fluidized-bed reactor for
CH4–CO2 reforming
Received 30th January 2013,
Accepted 10th April 2013
DOI: 10.1039/c3ra40511g
www.rsc.org/advances
Pengcheng Li,a
Jun Li,b
Qingshan Zhu,*b
Lijie Cui*a
and Hongzhong Lib
A Co–Al2O3 aerogel catalyst, which was prepared via a sol–gel process followed by supercritical drying, was
granulated to improve the fluidization quality. This showed that the fluidization of the aerogel catalyst
could be considerably improved by granulation. The effect of granulation on the activity and the stability
of the aerogel catalyst was investigated in a fluidized-bed reactor in the CH4–CO2 reforming reaction. It
was found that granulation can significantly improve the catalytic performance of the aerogel catalyst, e.g.
the granulated aerogel catalyst showed a much better catalytic stability and greater conversion of
methane as compared with the non-granulated aerogel catalyst. The improved catalytic performance of
this granulated catalyst was attributed to the better fluidization quality in the fluidized-bed reactor.
1. Introduction
Catalytic CH4–CO2 reforming has attracted much attention in
recent years, as it reforms two greenhouse gases, CH4 and CO2,
into syngas with lower H2/CO ratios, which is preferable to the
use of Fischer–Tropsch plants.1,2
Although all group VIII
transition metals, except osmium, can catalyze the CH4–CO2
reforming reaction,3
cobalt has frequently been used as the
active metal component of catalysts for this process because of
its high catalytic activity, wide availability and low cost.4–8
There are several ways to prepare the Co-based catalysts used
for the CH4–CO2 reforming process, such as impregnation,
sol–gel and coprecipitation.9–12
Among these preparation
methods, the sol–gel method has recently been used by many
researchers, because aerogel catalysts prepared by this method
show improved catalytic activity compared with catalysts
prepared by other methods.13–17
During the reforming process,
a fixed-bed reactor is generally used to operate the reaction.
However, in the fixed-bed reactor, the conversion of methane
and carbon dioxide is low, and the considerable amount of
carbon on the surface of the catalyst, which results from the
decomposition of CH4,18
causes the rapid deactivation of the
catalyst. This is because the distribution of the reactant gas is
heterogeneous in the whole region where reaction occurs,
which means the reactant gas and the catalyst cannot contact
efficiently. In light of the study by Effendi et al.,19
the whole
catalytic reaction region in the fixed-bed reactor can be divided
into two zones, the top zone and the bottom zone. At the
bottom region, the gas–solid contact is bad, which causes the
low conversion of the reactant gases. Additionally, the
deposited carbon cannot be removed from the gasification
with CO2, which further speeds up the deactivation of the
catalyst. Therefore, the improvement of the gas–solid contact
efficiency in the bed enables it to resist the deposition of
carbon and to improve the catalytic performance of the
catalyst.
Recent investigations have shown that operating the
reforming process in a fluidized-bed reactor can improve the
gas–solid contact efficiency, which can improve the catalytic
performance of the catalysts and the resistance to the
formation of carbon on the surface of the catalyst.20–22
For
instance, Chen et al.22
found that the superiority of the
fluidized-bed was independent of the catalyst used for this
process. In their study, for all of the catalysts that they used in
the CH4–CO2 reforming reaction, the catalytic performance in
the fluidized-bed reactor was superior to that in the fixed-bed
reactor. What’s more, the amount of carbon formed on the
surface of all of the catalysts in their study was less in the
fluidized-bed reactor than in the fixed-bed reactor. According
to Hao et al.,18
in the fluidized-bed reactor, the residence time
of the reactant gas is lengthened due to the high bed
expansion. Then the gas–solid contact efficiency can be
improved, which causes the much improved catalytic perfor-
mance of the catalysts. Moreover, this gives the catalysts an
opportunity to highly disperse and circulate between the CO2-
rich and CO2-deficient zones, which facilitates the gasification
of the deposited carbon. Therefore, the fluidized-bed reactor is
beneficial to the CH4–CO2 reforming process.
a
College of Chemistry and Chemical Engineering, University of Chinese Academy of
Sciences, 19A Yuquanlu, Beijing 100049, China. E-mail: ljcui@ucas.ac.cn
b
State Key Laboratory of Multiphase Complex Systems, Institute of Process
Engineering, Chinese Academy of Sciences, Beijing 100190, China.
E-mail: qszhu@home.ipe.ac.cn; Fax: +86 10 62536108
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However, it is difficult to fluidize the aerogel catalyst
particles in the fluidized-bed reactor because of the strong
cohesive forces among the particles.23,24
Consequently, there
is the need to employ methods to improve the flow
characteristics of these nanoparticles in the fluidized-bed. It
is well known that field-assisted fluidization, for example by
magnetic and electric fields, and ultrasound, can enhance the
fluidization quality.25
Many researchers have used magnetic
field-assisted fluidized-beds to improve the fluidization of the
nanoparticles.26–28
In the study of Chen et al.,26
the fluidiza-
tion of the aerogel catalyst was improved significantly in the
magnetic field-assisted fluidized-bed, which enhanced the
catalytic performance and the resistance to carbon deposition.
Nevertheless, the technology of the magnetic field-assisted
fluidized-beds for the application in industry is still not well-
developed. Furthermore, additional facilities are required to
produce the magnetic field, which increases the operational
costs of the reforming process and the complexity of the
system and its operation. Therefore, a much more low-cost
and convenient method should be employed to improve the
flow characteristics of the catalyst nanoparticles. It is well
known that granulation is a traditional and developed method
for improving the flow properties of fine particles.29
Zhu
et al.30
used granulation to tackle the defluidization of
ultrafine hematite powder in the fluidized-bed. Moreover,
compared to the magnetic fluidized-bed, granulation is an
easier and inexpensive way to improve the fluidization of
nanoparticles. Consequently, granulation may be a good way
to improve the catalytic performance of the aerogel catalysts in
the fluidized-bed. To our best knowledge, such granulation of
aerogel catalysts for CH4–CO2 reforming in the fluidized-bed
reactor has not been reported.
In the present work, a Co–Al2O3 aerogel nanoparticle
catalyst was granulated using ethanol as the bridging agent.
The fluidization behavior of the aerogel catalyst both with and
without granulation was investigated. The amount of carbon
on the surface of both of the catalysts was determined by a
carbon–sulfur analyzer. The catalysts were characterized by
XRD, BET and FESEM.
2. Experimental methods
2.1 Catalyst preparation
The preparation of the aerogel catalyst has been reported in
previous papers13,18,26,31
and will be briefly summarized here.
The 20 wt% Co–Al2O3 aerogel catalyst was synthesized using
Al(NO3)3?9H2O (Sinopharm Chemical Reagent Co., Ltd,
Beijing, China), Co(NO3)2?6H2O (Xilong Chemical Industry
Limited Company, Guangdong, China) and NH3?H2O (Beijing
Chemical Works, Beijing, China). Al(NO3)3?9H2O was dissolved
in deionized water to form a starting solution with a
concentration of 0.18 mol L21
(denoted as solution A).
Co(NO3)2?6H2O was dissolved in deionized water to form a
solution with a concentration of 0.1 mol L21
(denoted as
solution B). A 2.5 wt% NH3?H2O solution was added dropwise
to solution A under continuous and vigorous stirring at room
temperature until solution A obtained a pH of y7.5, and
formed a hydrogel. Subsequently, solution B was added
dropwise to the hydrogel and the pH of the solution was
adjusted to y9 by the 2.5 wt% NH3?H2O solution. The
resultant hydrogel was then aged for 2 h at room temperature.
After that, the hydrogel was washed successively with
deionized water and absolute ethanol several times. The as-
obtained gel was treated for 1 h in an autoclave under the
supercritical drying conditions of ethanol (260 uC and 8.0
MPa). After releasing the ethanol vapor at 260 uC, the resultant
powder was cooled down to room temperature under a
continuous nitrogen flow. Finally, the powder was calcined
at 650 uC for 4 h in air to form the 20 wt% Co–Al2O3 aerogel
catalyst (denoted as CoAl). After calcination, the aerogel
catalyst was placed in an alumina crucible. Then, ethanol
was added dropwise to the aerogel catalyst, acting as an
adhesive. At the same time, the catalyst particle and ethanol
mixture was stirred with a glass rod until the powder became
viscous, followed by calcination at 500 uC for 2 h in air to
granulate the aerogel catalyst (denoted as G-CoAl). We
obtained the sintered catalyst at this stage. Finally, the
sintered catalyst was ground and sieved. Both CoAl and
G-CoAl were sieved to collect the catalyst particles with a size
of 150–250 mm.
2.2 Catalyst characterization
The BET surface area of the catalysts was characterized by the
nitrogen physisorption method at 77 K using an adsorption
instrument (Gemini V, Micromeritics, USA). The amount of
carbon on the surface of the catalysts was measured by a
carbon and sulfur analyzer (CS-344, LECO, USA). The crystal
structure of the catalyst was determined by an X-ray powder
diffractometer (XRD, X9 Pert MPD Pro, Panalytical,
Netherlands), using Cu-Ka radiation (l = 1.5408 Å). The
microstructure of various powders was observed by field-
emission scanning electron microscopy (FESEM, JSM-6700F,
JEOL, Japan).
2.3 Fluidization characterization
In the present study, the cold-model experiment was con-
ducted in a similar way to the previous report.26,27
A glass tube
(i.d. 20 mm) with a porous sintered plate was used as the
fluidized-bed. High-purity nitrogen from a compressed N2
tank was employed as the fluidization gas. The gas velocity was
measured and adjusted by a mass flow meter (D08-3B/ZM,
Sevenstar, China). A micromanometer (JYB-DZ, ColliHigh,
China) was used to measure the pressure drop above the
distributor of the bed. The pressure drop was recorded at
different gas velocities. When the full fluidization of the bed is
reached, the pressure drop fulfills the following equation:
SDP = mg (1)
Where DP is the pressure drop, S is the area of the bed, m is
the weight of the catalyst and g is the acceleration of gravity.
2.4 Evaluation of catalytic performance
Methane reforming using carbon dioxide was carried out over
both of the catalysts at 800 uC using a quartz reactor with an
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inner diameter of 18 mm at atmospheric pressure. For this
study, 0.2 g of catalyst was used. Prior to the reaction, both
catalysts were reduced in situ in a H2:N2 (volumetric ratio of
1 : 1) gas mixture with a flow rate of 200 mL min21
. The
temperature was ramped by 10 uC min21
up to 800 uC and held
for 1 h. The gas flow rate of the reactants was 300 mL min21
(fluidizing velocity 2 cm s21
) with a CH4:CO2:N2 molar ratio of
1 : 1 : 1. The effluent gas was first cooled in an ice–water trap,
which was followed by composition analysis using a gas
chromatograph (SP3420, BEIFEN, China) equipped with 13X
and GDX-104 columns. The conversion of CH4 and CO2 and
the selectivity of H2 and CO were calculated by eqn (2)–(5):
x(CH4)%~
FCH4,in
{FCH4,out
FCH4,in
|100 (2)
x(CO2)%~
FCO2,in
{FCO2,out
FCO2,in
|100 (3)
s(H2)%~
FH2,out
2(FCH4,in
{FCH4,out
)
|100 (4)
s(CO)%~
FCOout
(FCH4,in
{FCH4,out
)z(FCO2,in
{FCO2,out
)
|100 (5)
where Fi = Ftotal 6 Ci, with x, s, F, and Ci representing the
conversion, selectivity, gas flow rate and molar fraction of the
ith species in the feed gas or the effluent gas, respectively. The
carbon balance across the reactor was within ¡5%.
3. Results and discussion
3.1 Catalyst characterization
Fig. 1 shows the XRD patterns of the calcined and reduced
samples of the CoAl and G-CoAl catalysts. It can be seen that
for both catalysts, only the cubic CoAl2O4 phase, with the
characteristic diffraction peaks at 2h = 31.5u, 37.1u, 45.0u,
59.9u, 66.0u and 77.5u, was observed, as illustrated in Fig. 1(a)
and (b). The XRD pattern showed that granulation did not
affect the phases formed after the granulation. However, the
diffraction peaks at 2h = 37.1u and 66.0u were narrowed, which
shows that the crystallinity of G-CoAl was much better than for
CoAl. Fig. 1(c) and (d) showed that after the reduction at 800 uC
for 2 h, the cobalt species in CoAl2O4 were reduced to metallic
cobalt in both catalysts. The diffraction peaks at 2h = 44.2u,
51.4u and 75.9u for G-CoAl were much narrower than the same
peaks for CoAl. This shows that a well-developed metallic
crystalline phase formed for G-CoAl, while the metallic
crystalline phase for CoAl was not well-developed. The active
metal size was calculated by the Scherrer equation:
D~
Rl
b cos h
(6)
where D is the active metal size, R is the Scherrer constant
(0.9), l is the X-ray wavelength (1.5408 Å), b is the half-peak
width (radian) and h is the diffraction angle. It can be foreseen
that the active metal size will increase due to the granulation.
As can be seen in Table 1, the active metal size of G-CoAl is
28.7 nm, while the value of CoAl is only 18.4 nm, as estimated
by the Scherrer equation. TEM was used to investigate the size
distribution of the active metal particles and the results are
shown in Fig. 2 and Table 1. TEM also showed that the active
metal size increased after granulation.
Considering the combination of the particles which causes
the increase in the active metal particle size, it is possible that
the surface area and the density could change significantly.
This is true for the bulk density, which increased from 0.039 g
mL21
to 0.312 g mL21
after granulation, as illustrated in
Table 1. However, Table 1 shows that the surface area did not
change much after the catalyst was granulated and sintered.
This difference can be explained by the granulated catalyst
possessing larger pores, which causes the increase in the bulk
density and has little influence on the surface area. It is well
known that a large catalyst surface area can improve the
dispersion of the active metal.32
During the reforming process,
the metal is the active site to catalyze the reaction. So it is easy
to see that the active site does not decrease considerably after
granulation. From the discussion above, it can be seen that the
influence of the granulation process on the properties of the
aerogel catalyst is insignificant.
3.2 Fluidization characterization
In order to study the influence of granulation on the
fluidization behavior of the aerogel catalyst, one gram of each
catalyst was used to study the fluidization behavior using the
fluidized-bed. Fig. 3(a) shows the bed pressure drop curve of
the CoAl catalyst. It can be seen that during the fluidization of
CoAl, there are several stages, such as slugging, channeling,
disrupting, and agglomerate fluidization with the increase of
gas velocity. This means that the fluidization of CoAl is
unstable in the fluidized-bed, which is similar to the
fluidization behavior of other aerogel catalysts.26,27
However,
Fig. 3(b) shows that the fluidization of the G-CoAl catalyst was
Fig. 1 XRD patterns of CoAl and G-CoAl: (a) CoAl after calcination at 650 uC for
4 h, (b) G-CoAl after calcination at 500 uC for 2 h, (c) CoAl after further reduction
at 800 uC for 2 h, (d) G-CoAl after further reduction at 800 uC for 2 h.
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totally different. As the gas velocity gradually increased with
time, the pressure drop of G-CoAl almost increased steadily
until it reached a stable value of 29 Pa. This value is almost
equal to the theoretical pressure drop for full fluidization, 29.2
Pa (eqn (1)), while Fig. 3(a) showed that the largest value of the
bed pressure drop for CoAl was only 15 Pa. The low bed
pressure drop for the CoAl catalyst is caused by channeling in
the fluidized bed. It is obvious that although the pressure drop
of CoAl reached a relatively stable value, the catalyst particles
are only partially fluidized in the fluidized-bed. Therefore, it
can be seen that G-CoAl fluidizes better than CoAl in the
fluidized-bed. The superior fluidization of the G-CoAl catalyst
means a better gas–solid contact in the gas–solid reaction
system. Consequently, the gas–solid contact efficiency can be
improved by granulating the aerogel catalyst, which should be
beneficial to the catalytic performance during the CH4–CO2
reforming reaction.
Table 1 Textural properties of the aerogel catalyst with and without granulation
Sample
BET surface area
(m2
g21
)
Bulk density
(g mL21
)
Active metal size of the
reduced samplea
(nm)
Active metal size of the
reduced sampleb
(nm)
CoAl 179.2 0.039 19.7 18.4
G-CoAl 165.9 0.312 29.7 28.7
a
Estimated by TEM. b
Calculated from the (2 0 0) peak using the Scherrer equation.
Fig. 2 TEM images (left) and metal particle size distributions (right) of (a) CoAl and (b) G-CoAl.
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3.3 Catalytic performance
The characterization of the catalysts and fluidization showed
that granulation may improve the catalytic performance of the
aerogel catalyst in the fluidized-bed reactor. Thus methane
reforming with carbon dioxide was carried out over the CoAl
and G-CoAl catalysts in the fluidized-bed reactor, under the
same conditions, to study the effect of granulation on the
catalytic stability and activity. Fig. 4 and 5 show the stability of
both of the catalysts under the same conditions during the
reforming process. It turned out that for the CoAl catalyst, the
methane conversion decreased gradually with the time on
stream, indicating low catalytic stability, while the G-CoAl
catalyst showed quite good catalytic stability. It was also found
that the reproducibility of methane conversion was quite poor
for the CoAl catalyst, where significant differences were
recorded in different tests under identical conditions, as
illustrated in Fig. 4. The poor reproducibility can be mainly
attributed to the unstable fluidization of the CoAl catalyst. In
contrast, the G-CoAl catalyst showed very good reproducibility,
as illustrated in Fig. 5.
To compare the catalytic activity and stability of the
catalysts, the conversion and selectivity of the catalysts as a
function of time on stream are illustrated in Fig. 6. Since the
catalytic performance of the CoAl catalyst fluctuates signifi-
cantly under the same conditions, the best catalytic result was
chosen to compare with the results of G-CoAl. Fig. 6(A) and (B)
show that G-CoAl exhibits greater activity and stability, even
when compared with the best results of the CoAl catalyst. For
instance, the initial conversion of methane for G-CoAl, which
was close to the thermodynamic equilibrium conversion, was
5% greater than that for CoAl. Additionally, the conversion of
methane and carbon dioxide for G-CoAl remained nearly
constant for up to seven hours, while the CoAl catalyst
gradually deactivated from the beginning of the operation.
After an operation time of 25 h, the CH4 conversion of the
G-CoAl catalyst decreased by only 7%, while a 33% decrease
was recorded for the CoAl catalyst, as illustrated in Fig. 6(A).
The discrepancy in the activity and stability of the catalysts is
also caused by the different fluidization behavior of the
catalysts in the fluidized-bed. Under the reaction conditions,
G-CoAl fluidizes better than CoAl, which improves the gas–
solid contact efficiency. Thus the activity and stability of
G-CoAl are much better than that of CoAl. Fig. 6(C) and (D)
show the selectivity of H2 and CO for both catalysts. It
demonstrates that the selectivity of CO for both catalysts was
obviously greater than that of H2. This is because during the
process of reforming, the reverse water gas shift (RWGS)
reaction (eqn (7)) occurred simultaneously,33,34
which can be
proved by the water detected in the outlet of the reactor.
CO2 + H2 = CO + H2O, DrH298 = 41 kJ mol21
(7)
According to many researchers, carbon deposition is one of
the main causes of the deactivation of the catalyst during
Fig. 3 Pressure drop of the reduced (a) CoAl and (b) G-CoAl catalysts in the
fluidized-bed.
Fig. 4 The conversion of CH4 as a function of the time on stream over CoAl in
the fluidized-bed reactor under identical conditions, to show the reproducibility
of using CoAl for CH4–CO2 reforming. Reaction conditions: 800 uC, 0.1 MPa, 0.2
g catalyst, 90 000 mL g21
h, CH4 : CO2 : N2 = 1 : 1 : 1.
Fig. 5 The conversion of CH4 as a function of the time on stream over G-CoAl in
the fluidized-bed reactor under identical conditions, to show the reproducibility
of using G-CoAl for CH4–CO2 reforming. Reaction conditions: 800 uC, 0.1 MPa,
0.2 g catalyst, 90 000 mL g21
h, CH4 : CO2 : N2 = 1 : 1 : 1.
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methane reforming with carbon dioxide.35–37
The different
carbon deposition behavior in this study may cause the
difference in the deactivation phenomena. Thus the spent
catalysts were characterized to investigate the carbon deposi-
tion on the surface of the catalysts. As illustrated in Fig. 7(a) by
the XRD results, there are very strong peaks from carbon for
the spent CoAl catalyst, indicating severe carbon deposition
during the reforming process. It is well known that in the
reforming reaction there are various forms of carbon on the
surface of the catalyst, such as atomic, amorphous and
graphitic carbon.38–40
XPS analysis was used to confirm the
form of carbon which was present on the surface of the
catalysts. As can be seen in Fig. 8, both CoAl and G-CoAl show
a peak of carbon species at a binding energy of 284.8 eV, which
can be assigned to the graphite phase. Therefore, the obvious
peak from the XRD analysis of CoAl is a result of graphite on
the surface. The amount of carbon on the surface of the
catalysts was determined by carbon and sulfur analysis.
According to the results in Table 2, the amount of carbon on
the surface of CoAl is 83.9 wt%, while that on the surface of
G-CoAl is only 1.9 wt%. The FESEM results in Fig. 9(a) also
indicated that there was a great deal of carbon on the surface
of CoAl, which should be responsible for the deactivation.
Consequently, carbon deposition is the main cause of the
deactivation of CoAl. In order to find out the reason for the
slight deactivation of G-CoAl, BET was used to determine the
surface area of the spent catalysts. The results are shown in
Table 2. It can be seen that the surface area of G-CoAl
decreased by 12.2%, while the surface area of CoAl decreased
by only 6.5%. Therefore, the slight deactivation of G-CoAl
results from the decrease in surface area of the active site.
As discussed above, a large amount of graphitic carbon
deposition resulted in the deactivation of CoAl, while the
catalytic performance of G-CoAl is much more stable in the
fluidized-bed reactor. The only difference in the catalytic
process is the fluidized behavior of the catalysts.
Consequently, the fluidization of the catalysts plays a very
important role in the deactivation mechanism of the catalysts
for methane reforming with carbon dioxide. For CoAl, the
fluidization quality is very poor, and only partial fluidization
Fig. 6 The conversion of CH4 (A) and CO2 (B), and the selectivity of H2 (C) and CO (D) as a function of the time on stream over CoAl and G-CoAl in a fluidized-bed
reactor. Reaction conditions: 800 uC, 0.1 MPa, 0.2 g catalyst, 90 000 mL g21
h, CH4 : CO2 : N2 = 1 : 1 : 1.
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was achieved. The unfluidized particles lie in a reductive
atmosphere which is CO2-deficient, and it is favorable for the
generation of carbon on the surface of CoAl. In addition, the
gas–solid efficiency in the reactor is very poor, which causes
the low activity of the catalyst. In turn, the low gas–solid
efficiency means that carbon, from the dissociation of CH4,
cannot be easily gasified, which further causes the deactiva-
tion of the catalyst. However, G-CoAl can be very easily
fluidized in the fluidized-bed reactor. It is known that the good
fluidization of the catalyst in the fluidized-bed reactor allows
constant catalyst circulation, which has been proposed to be
helpful for carbon removal through CO2 gasification.18,41
What’s more, when the fluidization is improved, the gas–solid
contact efficiency is also much better, resulting in a more
homogeneous distribution of the reactants. Consequently, the
catalytic activity and stability of G-CoAl are much better than
those of CoAl.
4. Conclusions
A Co–Al2O3 aerogel catalyst was granulated using ethanol.
After granulating the aerogel catalyst, the fluidization
improves considerably, which leads to a better gas–solid
contact efficiency. Compared to the aerogel catalyst without
granulation, the granulated catalyst showed higher catalytic
activity and stability. The initial conversion of CH4 and CO2
nearly reaches the thermodynamic equilibrium using the
granulated catalyst, which is superior to the aerogel catalyst
without granulation. The granulated catalyst exhibited a
longer stable time than the non-granulated catalyst. The
comparative study demonstrates that the improvement of
fluidization by granulation has a significant influence on
catalyst activity and stability. Carbon deposition was the main
cause of the deactivation of the non-granulated catalyst. There
was a large amount of carbon on the surface of the aerogel
catalyst, while there is almost no carbon on the surface of the
granulated catalyst. The superior resistance of the granulated
catalyst to carbon deposition is attributed to the improved
gas–solid contact efficiency in the fluidized-bed.
Fig. 7 XRD patterns of the spent catalysts in the fluidized-bed reactor after 25 h
of reaction: (a) CoAl, (b) G-CoAl.
Fig. 8 XPS spectra of C 1s in the spent (a) CoAl and (b) G-CoAl.
Table 2 Catalytic activities, BET and coke deposition of the spent catalysts
Sample Highest conversion of CH4 Final conversion of CH4
a
BET surface areaa
(m2
g21
) Amount of cokeab
(wt%)
CoAl 0.90 0.57 167.5 83.9
G-CoAl 0.95 0.88 145.7 1.9
a
Tested after 25 h on stream. b
Determined by carbon and sulfur analysis.
Fig. 9 FESEM images of the spent (a) CoAl and (b) G-CoAl in the fluidized-bed
reactor.
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Acknowledgements
The authors would like to acknowledge the financial support
from the National Basic Research Development Program
(grant no. 2009CB219904) and from the National Special
Project for Development of Major Scientific Equipment (grant
no. 2011YQ12003908).
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