Synthesis of ordered mesoporous carbon materials and their catalytic performance in dehydrogenation of propane to propylene

Article abstract of DOI:10.1016/j.cattod.2011.08.022

Monolithic mesoporous carbons were prepared through a simple autoclaving method using citric acid as catalyst instead of HCl. The presence of citric acid plays an important role in determining the structural ordering of the resultant mesoporous structure due to the -COOH groups which can enhance hydrogen interaction between structural directing agent of triblock copolymer F127 and polymeric carbon precursor of resorcinol-formaldehyde resins. The obtained carbons have a hexagonal pore system, uniform pore size of ～5.0 nm and high BET surface area of ～758 m²/g. The prepared mesoporous carbons were used as catalyst for dehydrogenation of propane, exhibiting high catalytic activity and stability. After 50 h time-on-stream, the propane conversion of 12.1% was observed with propylene selectivity of 95.1% in the direct dehydrogenation process, while the propane conversion of 20.1% with propylene selectivity of 25.8% in oxidative dehydrogenation process. It has been found that the surface basic groups are active sites.

Full text of DOI:10.1016/j.cattod.2011.08.022

Catalysis Today 186 (2012) 35–41
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Synthesis of ordered mesoporous carbon materials and their catalytic
performance in dehydrogenation of propane to propylene
Lei Liua, Qing-Fang Denga, Bao Agulaa,b, Tie-Zhen Renc, Yu-Ping Liud,
Bao Zhaorigetub, Zhong-Yong Yuana,∗
a Institute of New Catalytic Materials Science, Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry,
Nankai University, Tianjin 300071, China
b College of Chemistry and Environmental Science, Inner Mongolia Normal University, Huhhot 010022, China
c School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, China
d Research Center for Analytical Sciences, College of Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 May 2011
Received in revised form 3 August 2011
Accepted 11 August 2011
Available online 3 September 2011
Monolithic mesoporous carbons were prepared through a simple autoclaving method using citric acid as
catalyst instead of HCl. The presence of citric acid plays an important role in determining the structural
ordering of the resultant mesoporous structure due to the –COOH groups which can enhance hydrogen
interaction between structural directing agent of triblock copolymer F127 and polymeric carbon pre-
cursor of resorcinol–formaldehyde resins. The obtained carbons have a hexagonal pore system, uniform
pore size of ∼5.0 nm and high BET surface area of ∼758 m2/g. The prepared mesoporous carbons were
used as catalyst for dehydrogenation of propane, exhibiting high catalytic activity and stability. After 50 h
time-on-stream, the propane conversion of 12.1% was observed with propylene selectivity of 95.1% in
the direct dehydrogenation process, while the propane conversion of 20.1% with propylene selectivity of
25.8% in oxidative dehydrogenation process. It has been found that the surface basic groups are active
sites.
Keywords:
Ordered mesoporous carbon
Citric acid
Dehydrogenation
Propane
Propylene
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
Synthesis of ordered mesoporous carbon materials (OMCs)
with various structures has achieved great progress. Nanocasting
Porous carbon materials have attracted much interest in catal-
ysis, especially metal-free catalysis, due to their unique porous
structure and chemical properties. During the last three decades,
activated carbon (AC) itself was shown to be a promising catalyst
for the oxidative dehydrogenation (ODH) reaction [1,2]. However,
the commercialized AC as catalyst for ODH reaction is not possible,
because its low stability in an oxidative atmosphere hindered the
potential use of AC. Most recently, nanocarbons have been found
to be efficient in ODH of ethylbenzene and alkanes [3–10], which
provided a new way in the area of catalysis. With the large sur-
face area and uniform pore sizes, mesoporous carbon materials
offer possibility of creating reaction sites and molecular confine-
ment that permit the selective formation of reaction products in
heterogeneous catalysis. However, little effort to date has been
focused on the dehydrogenation of propane to propylene over
mesoporous carbon materials, although propylene is an indispens-
able raw material for numerous products.
method from mesoporous silica is complicated, though it has been
extensively developed to synthesize OMCs [11–13]. More recently,
facile routes were developed to fabricate OMCs by assembly of
block copolymers with polymeric carbon precursor followed by
removal of block copolymers and carbonization [14–18]. Based
on the organic–organic self-assembly, the OMCs obtained by the
evaporation induced self-assembly method are always in the
form of films [14–16]. Although such a synthesis of OMCs is a
great improvement compared to nanocasting pathway, the direct
preparation of mesoporous carbons with well-ordered pore system
and perfect macroscopic morphology is still a great challenge. In
our previous work, mesoporous carbons were obtained by using
triblock copolymer F127 as template and resorcinol/formaldehyde
resol as carbon precursor in the presence of HCl [19]. Herein,
we report a facile one-pot approach in the aqueous phase under
mild reaction conditions to synthesize mesoporous carbons with
ordered mesoporous structure and perfect macroscopic mor-
phology. The crucial difference to previous work is the presence
of citric acid as catalyst which catalyzed both the formation
of resorcinol–formaldehyde resol and the assembly of ordered
mesostructure. The obtained ordered carbon samples were used
as catalyst in the direct dehydrogenation (DH) and oxidative
∗
Corresponding author. Tel.: +86 22 23509610; fax: +86 22 23509610.
E-mail address: zyyuan@nankai.edu.cn (Z.-Y. Yuan).
0920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2011.08.022

36
L. Liu et al. / Catalysis Today 186 (2012) 35–41
dehydrogenation (ODH) of propane to propylene. And it has been
revealed that the mesoporous carbon catalyst can efficiently cat-
alyze the dehydrogenation reaction, despite of no metal deposited,
exhibiting high catalytic activity and stability.
the gas reactant contained 5 vol% propane and a balance of nitro-
gen (total flow rate = 40 mL/min). The operating temperature is
between 673 and 873 K. ODH was performed with the gas reactant
contained 10 vol% propane, 10 vol% oxygen and balancing nitro-
gen (total flow rate = 50 mL/min) at temperatures between 523 and
673 K with catalyst loading of 500 mg. Propane (C3H8) conversion
and selectivity to products have been calculated as follows:
2. Experimental
2.1. Synthesis
moles of C3 reacted
moles of C3 fed
C3H8 Conversion (mol %) =
× 100
The OMCs were prepared through an autoclaving method with
the molar ratio of formaldehyde to resorcinol of 2:1. In a typical
synthesis, 1.65 g of resorcinol and 1.5 g of poly (ethylene oxide)-
poly (propylene oxide)-poly (ethylene oxide) copolymer of Pluronic
F127 (PEO106–PPO70–PEO106, Mw = 11,500) was dissolved in a mix-
ture of 20 mL of water and 20 mL of ethanol. 0.2 g of HCl (37%) or
2.1 g of citric acid was then added to the above solution. After 1 h
of stirring, 2.5 g of 37% formaldehyde solution was added drop-
wise under tempestuously stirring, resulting in pH = 6.0–7.0 of the
reaction system. The reaction mixture was then transferred to a
Teflon-lined autoclave and heated at 60 ◦C for 2 days. The obtained
products were collected by filtration, washed with water and dried,
and then carbonized at 600 ◦C for 3 h. The final products were
named as HOMC and COMC when HCl and citric acid were used
as catalysts, respectively.
ꢀ
ꢁ
moles of product i formed
moles of C3 reacted
Ni
Selectivity (mol %)=
×
× 100
NC
3
3. Results and discussion
Organic–organic self-assembly depends on the hydrogen bond-
ing between resins containing abundant hydroxyl groups and
the polyethylene oxide (PEO) segments of the self-assembled tri-
block copolymers [14–19]. The previous reported works usually
employed HCl as catalyst to polymerize the formation of phe-
nol resin. However, much halogenide ions were introduced to the
reaction system, which is not friendly to the environmental. In
this work, citric acid was used to friendly catalyze the forma-
tion of resorcinol–formaldehyde resin and enhances the interaction
between resins and F127, attributing to the abundant –COOH
groups.
2.2. Characterization
Transmission electron microscopy (TEM) measurements were
performed on a Philips Tecnai F20 microscope at 200 kV. All sam-
ples subjected to TEM measurements were ultrasonically dispersed
in ethanol and drop-cast onto copper grids covered with carbon
film. Small angle X-ray scattering (SAXS) experiments were per-
formed on a Bruker Nanostar small angle X-ray scattering system.
Nitrogen adsorption and desorption isotherms were measured on a
Quantachrome NOVA 2000e sorption analyzer at 77 K. Before mea-
surements, the samples were degassed in a vacuum at 200 ◦C for
at least 6 h. The Brunauer–Emmett–Teller (BET) method was uti-
lized to calculate the specific surface areas (SBET), the pore size
distributions were obtained using non-local density functional the-
ory (NLDFT) method, and the total pore volumes (Vtotal) were
estimated from the adsorbed amount at a relative pressure P/P0
of 0.980. X-ray photoelectron spectroscopy (XPS) measurements
were performed on a Kratos Axis Ultra DLD (delay line detector)
spectrometer equipped with a monochromatic Al Ka X-ray source
(1486.6 eV). All XPS spectra were recorded using an aperture slot
of 300 ␮m × 700 ␮m, survey spectra were recorded with a pass
energy of 160 eV, and high-resolution spectra with a pass energy of
40 eV. The binding energies (BE) were referenced to the C 1s peak of
contaminant carbon at 284.6 eV with an uncertainty of 0.2 eV. A
Shirley background was subtracted before fitting. The full width at
half maximum (FWHM) of the C1 peak was 1.0–1.2 eV, 2.0 0.2 eV
for the C2–C4 peaks and 2.5 0.2 eV for the C5 peaks. The C1 peak
had an asymmetrical shape, whereas the other peaks were sym-
metrical. The FWHM of the O 1s peak was 2.0 0.3 eV for O1–O4.
The Gauss–Lorentz ratio was maintained at values higher than
0.5. The temperature-programmed desorption (TPD) profiles were
obtained from a Quantachrome CHEMBET-3000 analyzer, consist-
ing of a U-shaped tubular micro-reactor, placed inside an electrical
furnace. The mass flow rate of the helium carrier gas (20 mL/min)
and the heating rate of the furnace (5 K/min) were controlled with
appropriate units.
Photographs of the obtained monolithic polymer and the corre-
sponding carbon materials are shown in Fig. 1. Short column-like
polymer (Fig. 1a, diameter of approx. 21 mm and height of approx.
5 mm) can be obtained in the presence of citric acid. The shape and
size of the obtained product can be easily tuned by changing the
size of the Teflon-lined autoclave. Carbonization causes the color
change of the polymer to black, but the shape is well retained,
and the obtained short column-like carbon is crack-free, even an
obvious shrinkage (31%) in size occurs (Fig. 1b, diameter of approx.
17 mm and height of approx. 3.5 mm).
In our previous work, it has been found that only poorly ordered
mesostructure can be obtained when the molar ratio of formalde-
hyde to resorcinol fixed at 2:1 and autoclaving for 2 days if HCl
was used as catalyst [19]. As the SAXS patterns shown in Fig. 1c.
HOMC represents a wide and poorly resolved peak, suggesting a
continuous structural distortion, though the orderly arranged pore
structures can be observed in the TEM image (Fig. 1d). COMC shows
a much stronger diffraction peak at q-value of 0.68 nm−1 that can
be indexed as (1 0) reflection associated with 2D hexagonal p6mm
symmetry. The well ordered regularity is also observed in TEM
image (Fig. 1e). This observation indicates that COMC has a higher
degree of hexagonal mesoscopic organization than HOMC. Since
the pH values of citric acid and HCl catalyzed reaction system are
quite similar (pH = 6.0–7.0), it is clear that citric acid plays an impor-
tant role in the formation of periodic mesostructure, attributing to
the abundant –COOH groups in citric acid which may enhance the
interaction between resol and F127 [20]. The intense (1 0) peak of
COMC reflects a d-spacing of 9.7 nm, which corresponds to a large
unit-cell parameter (a0 = 11.2 nm).
The textural properties of mesoporous carbons were deter-
mined by the nitrogen sorption analysis. As exhibited in Fig. 2, the
isotherms of the carbonized samples are of type IV with a clear
hysteresis loop at P/P0 = 0.4–0.7, indicating mesoporous character.
Meanwhile, the large volume adsorbed at the lower P/P0 = 0–0.1
implies the presence of microporosity. Type-H1 hysteresis loops
and narrow pore size distributions centered at around 5 nm were
observed for COMC. From the physicochemical properties summa-
rized in Table 1, it can be seen that the pore size, surface area and
2.3. Catalytic testing
Catalytic tests were performed in a stainless steel, fixed-bed
flow microreactor at atmospheric pressure. In the DH process,

L. Liu et al. / Catalysis Today 186 (2012) 35–41
37
Fig. 1. Photographs of monolithic polymer (a) and carbon (b), and SAXS patterns (c) and TEM images of HOMC (d) and COMC (e).
pore volume enlarged when citric acid used as catalyst instead of
HCl. The t-plot calculation reveals that the micropore volume of
COMC is a little larger than that of HOMC. Since citric acid can
enhance the hydrogen bond interaction between template and
resins, the PEO segments of triblock copolymers could embedded
into the resins during polymerization process, and the microp-
orosity in the synthesized carbons may result from the removal
of PEO block which makes some disfigurement in the pore wall of
the final products [21]. Thus, one can see that mesoporous carbon
with ordered hexagonal pore structure and large surface area can
be fabricated in the presence of citric acid.
and COMC were tested as catalysts for DH of propane to propy-
lene. For comparison, three other types of carbon materials, AC,
carbon nanotubes (CNTs) and graphitic carbon (GC), were also
investigated. The activity of the catalyst samples for DH of propane
was tested in a fixed-bed tubular reactor at atmospheric pressure
at 673–873 K. In addition to propylene being the target product,
methane, ethane and ethylene are also formed as by-products over
all the carbon catalysts. The C-balance of the inlet and outlet stream
indicates that lower hydrocarbons are cracking products. Among
these by-products, methane is the most dominating followed by
ethane and ethylene. Fig. 3 shows the initial activity at different
temperatures over different carbon catalysts. The conversion of
propane increased with the elevated reaction temperature, but the
Catalytic dehydrogenation of propane is an important route
for propylene synthesis. Herein, the mesoporous carbons HOMC
0.32
b
a
400
COMC
HOMC
COMC
0.24
HOMC
320
240
160
0.16
0.08
0.00
0.0
0.2
0.4
0.6
0.8
P0
1.0
0
3
6
9
12
Pore diameter (nm)
Relative pressure,
P
/
Fig. 2. Nitrogen sorption isotherms (a) and the corresponding pore size distribution curves (b) of HOMC and COMC.

38
L. Liu et al. / Catalysis Today 186 (2012) 35–41
Table 1
Textural properties and specific catalytic activities of different carbon catalysts.a
b
c
Sample
SBET (m2/g)
DDFT (nm)
VMicro (cm3/g)
Reaction rated
(mmol/g/h)
Hydrogen yield
(mmol/g/h)
Propaneconversion(%)
Propylene selectivity (%)
Initial
50 h
Initial
50 h
HOMC
COMC
ACe
675 (325)
758 (405)
956 (427)
212
4.7
5.1
1–12
2–20
–
0.14 (0.02)
0.16 (0.03)
0.29 (0.04)
0
35.1
51.3
18.3
18.8
13.4
14.5
32.2
20.1
22.6
17.7
9.0
6.5
21.6
10.3
12.1
5.2
–
–
20.1
66.1
89.0
53.3
87.5
93.9
25.2
78.5
95.1
74.6
–
–
25.8
47.8
16.7
17.1
12.5
–
CNTs
GCe
4
0
COMCf
758 (447)
5.1
00.16 (0.01)
a
Data in the parentheses are for the used catalysts after 50 h of reaction.
The pore diameter is calculated using NLDFT method.
The micropore volume is calculated from the t-plot method.
The reaction rates were obtained after reaction for 2 h depicted as propylene formation.
AC and GC were purchased from Tianjin Chemical Corp.
The data present were obtained when COMC was used as catalyst for ODH.
b
c
d
e
f
selectivity to propylene slightly decreased for both HOMC and
COMC. The conversions of propane for COMC are 15.9% and 22.6%
at 823 and 873 K, respectively. Slightly lower conversions were
observed for HOMC, which are 13.9% and 20.1% at 823 and 873 K,
respectively. It is worthwhile to note that the selectivity of propy-
lene over HOMC is much lower than that on COMC, which may
be due to its poorly ordered mesoporous structure, hindering the
transmission of propylene and impeding its releasing from the pore
system. Much lower catalytic activities were observed for other
carbons with conversions between 5% and 14.0% at 873 K, although
the higher selectivity to propylene occurred at higher temperature
range.
Fig. 4 shows the results of propane conversion and selectivity to
propylene as a function of time over different carbon catalysts. After
a short induction period, COMC, HOMC and AC stably catalyze the
propylene formation during a reaction lasting 50 h under the oper-
ating conditions (Fig. 4a). The final propane conversions are 12.1%,
10.3% and 5.2% for COMC, HOMC and AC, with the final propylene
selectivity of 95.2%, 78.5% and 74.6%, respectively. Whereas, severe
deactivation of the nanostructured carbons were detected (Fig. 4b).
After 10 h, the conversion of propane is as low as 4.5% over CNTs,
yielding 4.4% propylene. GC is much less active with propane con-
version of 2.4%, yielding 1.4% propylene after only 4 h on stream.
The reaction rate as the amount of propylene produced per hour is
presented in Table 1, COMC displays a value of 51.3 mmol/g/h, up
to approximately 1.5 times of HOMC, and 3–4 times of other tested
carbons. COMC is much more active than other carbon materials,
displaying a superior catalytic performance. Its catalytic activity
is comparable with the binary In–Al–O nanocomposites for the
dehydrogenation of propane in the presence of CO2 or NO2, afford-
ing steady propane conversion approximately 20% during 30 h on
stream [22–24].
Numerous studies on the improvement of existing chromia and
platinum based catalysts and the development of vanadia-based
and Sn-promoted catalysts have been reported [25–32]. However,
the major challenges associated with these catalytic systems are
the coking and cracking which influence the catalyst stability and
propylene selectivity, respectively. It is worthwhile to note that
the propylene selectivity is higher than 90% and remained almost
unchanged for COMC over 50 h (Fig. 4a), which is much higher than
the K or Na promoted Pt/Sn catalysts with propylene selectivity
of only 10–30% [25,26]. The catalytic stability of COMC measured
by the reduction of propylene yield is 42.5% after 50 h, which is
superior to the extensively discussed Pt-based catalysts supported
on amorphous supports or zeolites for propane dehydrogenation,
with the reduction of propylene yield of 31.7% after only 4 h time-
on-stream [27,28]. Rare earth metals (La, Ce, Y) have been added
to Pt–Sn/Al2O3 catalysts to enhance the tolerance against catalyst
deactivation. However, the dehydrogenation performance of the
rare earth metals promoted Pt–Sn catalysts is still not satisfactory,
with the propylene yield reduced from 48% to 28.8% over the La
promoted catalysts after 2 h [29].
The carbon sample COMC was also tested for ODH of propane
to propylene, and the result is shown in Fig. 5. It is remarkable that
the conversion and selectivity increased with the temperature. The
conversion of propane increased from 10.4% to 21.6%, when the
temperature was changed from 623 to 673 K, while the selectivity
of propylene slightly increased from 20.1% to 25.2%. As the long
term stability test as a function of time-on-stream shown in Fig. 6,
after a short induction time at 673 K and at a flow rate of 50 mL/min,
a
25
20
100
b
COMC
HOMC
AC
80
60
CNTs
GC
15
10
5
COMC
HOMC
AC
CNTs
GC
40
20
0
0
700
750
800
850
700
750
800
850
Temperature ( K)
Temperature (K)
Fig. 3. The initial activity of DH process at different temperatures over different carbon catalysts. (a) Propane conversion and (b) selectivity of propylene.

L. Liu et al. / Catalysis Today 186 (2012) 35–41
39
100
80
60
40
20
0
100
a
b
80
60
COMC
CNTs
GC
HOMC
AC
40
20
0
0
2
4
6
8
10
0
10
20
30
40
50
Time (h)
Time (h)
Fig. 4. Propane conversion and propylene selectivity in the DH of propane to propylene over different carbon catalysts. (a) Mesoporous carbons (COMC and HOMC) and AC,
and (b) CNTs and GC. Reaction conditions: 0.40 g, 873 K, 5 vol% propane in nitrogen, 40 mL/min.
a steady propylene selectivity of 25.4% is achieved at a conversion of
25
20
15
10
5
21.2%. The high activity at the beginning of the reaction is accom-
panied by a slightly lower selectivity, but both level-off after 2 h.
The highly ordered COMC carbon is structurally stable during the
catalytic test of 50 h time-on-steam. AC was also tested for ODH of
propane to propylene, however, it yielded only cracked products
due to unavoidable combustion in the ODH process with high flow
rate [5,33–35].
COMC exhibited a very low selectivity to propylene in the ODH
process. It seems that the high surface area of COMC would lead to
the re-adsorption of the propylene even for short retention times,
rendering a further reaction with oxygen and therefore, a total oxi-
dation in the oxidizing feed-gas atmosphere (50 mL/min flow gas
with C3H8:O2:N2 = 1:1:8). This result is consistent with the previ-
ously reported CNTs used as catalyst for ODH of propane, while
the active sites generated in the oxidizing feed-gas atmosphere are
unselective and favor CO2 formation due to deep oxidation [6].
The robust catalytic activity of COMC and HOMC may be
related with their abundant surface oxygen groups. It is generally
assumed that each type of surface oxygen groups decomposes to
a defined product at different temperatures through temperature-
programmed methods. The acidic groups decomposed at
low temperatures (T < 900 K) and basic groups decomposed
Conversion
selectivity
Yield
0
600
624
648
672
Temperature (K)
Fig. 5. Conversion, selectivity and yield of ODH of propane to propylene over carbon
sample COMC at different temperatures.
30
25
(a)
(b)
20
15
Conversion
Selectivity
(c)
10
(d)
Yield
5
(e)
0
0
10
20
30
40
50
400
600
800
1000
1200
Time (h)
Temperature (K)
Fig. 6. Conversion, selectivity and yield of ODH of propane to propylene over COMC
at 673 K.
Fig. 7. TPD profiles of different carbons before reaction: (a) COMC, (b) HOMC, (c)
AC, (d) CNTs and (e) GC.

40
L. Liu et al. / Catalysis Today 186 (2012) 35–41
a
b
540
536
532
528
540
536
532
528
Binding energy, eV
Binding energy, eV
Fig. 8. XPS oxygen 1s spectra of samples COMC (a) and HOMC (b) before reaction. The spectra were normalized in the same intensity.
at temperatures above 900 K [36–39]. The TPD profiles of COMC,
HOMC and AC exhibit one peak with maximum at around 1070 K
(Fig. 7), which originated from carbonyls and quinone groups,
although the intensity of AC is much lower than that of COMC.
Nanostructured carbons were also applied to the TPD test. How-
ever, CNTs exhibit an extremely small peak at 550 K, corresponding
to the carboxylic acid groups, and a very board peak ranging from
600 to 1100 K, attributing to lactones, anhydrites, phenol and
carbonyl groups arising from HNO3 treatment during the syn-
thesis process [36]. GC represents no obvious peak in the tested
temperature, indicating that there are little functional groups in
the carbon surfaces, which may cause poor catalytic activity in the
dehydrogenation of propane.
The O 1s X-ray photoelectron spectra (XPS) of COMC and HOMC
confirm their oxygen-containing surface (Fig. 8). The deconvolution
of the O 1s spectrum reveals three different chemical environments
of oxygen, which could be assigned to unsaturated C O compo-
nents (531.0 eV), C–OH and C O in anhydrides (532.1 eV), C–O in
esters and anhydrides (533.3 eV) and adsorbed water (535.4 eV)
[40]. The total surface oxygen atomic concentrations in the samples
COMC and HOMC were estimated from XPS spectra to be 4.5% and
4.0%, respectively, and the corresponding unsaturated C O con-
centrations are 0.4%, and 0.25%, respectively. The presence of basic
sites has been reported as active sites during the dehydrogenation
reaction [6,41,42]. The sample with the highest carbonyl concen-
tration has the highest reaction rate, corresponding to the fact that
carbonyl–quinone groups are the active sites in the dehydrogena-
tion reaction [5].
for mass transport and good thermal stability [35]. AC is also active
in the DH of propane to propylene, but deactivates sharply at the
very beginning, although both carbon materials are characteristic
for the high-surface area. This may be as a result of the formed coke
blocking most of the micropores of AC and overlaping the active
sites. The specific surface area of the used COMC carbon after the
DH reaction is still as high as 405 m2/g, while the specific surface
area of activated carbon typically decreased from 956 to 427 m2/g.
The metal-oxides bring pollution to environment and the noble
metal based catalysts are expensive. The ordered mesoporous
carbons present high catalytic activity and stability in the dehy-
drogenation of propane, which is promising as an alternative to
metal-oxide catalysts and noble metal based catalysts for dehydro-
genation reactions of alkanes.
4. Conclusions
A
simple and environmentally benign method to pre-
pare monolithic OMCs was proposed from self-assembly of
resorcinol–formaldehyde and block copolymers catalyzed by cit-
ric acid. Well-ordered hexagonal structure was obtained as a result
of the enhanced driving force provided by citric acid, while poorly
ordered mesostructure was obtained when HCl was used at the
same conditions. The prepared ordered mesoporous carbons exhib-
ited high activity in dehydrogenation of propane to propylene. The
basic oxygen groups are the active sites for selective dehydrogena-
tion. The regeneration of the active sites is achieved by oxidation of
C–OH in ODH process and thermal dehydrogenation in DH process.
The BET surface area and pore volume of COMC seriously
decreased (Table 1, data in the parentheses) after both DH and ODH
reaction, e.g., the BET surface area of COMC decreased from 758
to 405 m2/g after used as catalyst for DH process. Meanwhile, it
is worthwhile to note that the micropores nearly disappeared for
COMC carbon catalysts after long time reaction, which may be the
result of the formation of coke during the reaction [35]. The values
of carbon balance in the calculation between propane conversion
and the formed products slightly higher than unit also indicated
the coke formation during the reactions. Correspondingly, a slight
deactivation process was observed. However, the high stability
shown in Table 1 indicates that the loss of the surface area at the
very beginning of the reaction did not have a strong influence to the
catalytic performance of the carbon catalysts. The coke formation
at the beginning of the reaction may be an active phase as reported
by Cadús et al. for Al2O3 [43].
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (20973096, 21076056), the National Basic Research
Program of China (2009CB623502), and the Program for Changjiang
Scholars and Innovative Research Team in University (IRT0927).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.cattod.2011.08.022.
References
[1] M.F.R. Pereira, J.J.M. Orfao, J.L. Figueiredo, Appl. Catal. A: Gen. 184 (1999)
153–160.
[2] M.F.R. Pereira, J.J.M. Orfao, J.L. Figueiredo, Appl. Catal. A: Gen. 196 (2000) 43–54.
[3] J.J. Delgado, D.S. Su, G. Rebmann, N. Keller, A. Gajovic, R. Schlögl, J. Catal. 244
(2006) 126–129.
COMC used for both DH and ODH of propane exhibits an unusual
stability that can be related with its unique structure: the larger,
but well-ordered porosity of mesoporous carbon is advantageous

L. Liu et al. / Catalysis Today 186 (2012) 35–41
41
[4] J. Zhang, X. Liu, R. Blume, A.H. Zhang, R. Schlögl, D.S. Su, Science 322 (2008)
73–78.
[23] M. Chen, J. Xu, Y.M. Liu, Y. Cao, H.Y. He, J.H. Zhuang, Appl. Catal. A: Gen. 377
(2010) 35–41.
[5] J. Zhang, D.S. Su, A.H. Zhang, D. Wang, R. Schlögl, C. Hébert, Angew. Chem. Int.
Ed. 46 (2007) 7319–7323.
[24] M. Chen, J.L. Wu, Y.M. Liu, Y. Cao, K.N. Fan, Catal. Commun. 12 (2011)
1063–1066.
[6] B. Frank, J. Zhang, R. Blume, R. Schlögl, D.S. Su, Angew. Chem. Int. Ed. 48 (2009)
6913–6917.
[7] G. Mestl, N.I. Maksimova, N. Keller, V.V. Roddatis, R. Schlögl, Angew. Chem. Int.
Ed. 40 (2001) 2066–2068.
[8] D.S. Su, N.I. Maksimova, G. Mestl, V.L. Kuznetsov, V. Keller, R. Schlögl, N. Keller,
Carbon 45 (2007) 2145–2151.
[9] C.D. Liang, H. Xie, V. Schwartz, J. Howe, S. Dai, S.H. Overbury, J. Am. Chem. Soc.
131 (2009) 7735–7741.
[25] S.B. Zhang, Y.M. Zhou, Y.W. Zhang, L. Huang, Catal. Lett. 135 (2010) 76–82.
[26] Z.Y. Duan, Y.M. Zhou, Y.W. Zhang, X.L. Sheng, M.W. Xue, Catal. Lett. 141 (2011)
120–127.
[27] L.H. Huang, B.L. Xu, L.L. Yang, Y.N. Fan, Catal. Commun. 9 (2008) 2593–2597.
[28] M.S. Kumar, D. Chen, A. Holmen, J.C. Walmsley, Catal. Today 142 (2009) 17–23.
[29] B.K. Vu, M.B. Song, I.Y. Ahn, Y.W. Suh, D.J. Suh, W. Kim, H.L. Koh, Y.G. Choi, E.W.
Shin, Catal. Today 164 (2011) 214–220.
[30] J.M. McNamara, S.D. Jackson, D. Lennon, Catal. Today 81 (2003) 583–587.
[31] J.N.J. van Lingen, O.L.J. Gijzeman, B.M. Weckhuysen, J.H. van Lenthe, J. Catal. 239
(2006) 34–41.
[10] B. Frank, M. Morassutto, R. Schomcker, R. Schlögl, D.S. Su, ChemCatChem 2
(2010) 644–648.
[11] S. Jun, S.H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, Z. Liu, T. Ohsuna, O. Terasaki, J.
Am. Chem. Soc. 122 (2000) 10712–10713.
[12] R. Ryoo, S.H. Joo, M. Kruk, M. Jaroniec, Adv. Mater. 13 (2001) 677–681.
[13] R. Ryoo, S.H. Joo, S. Jun, J. Phys. Chem. B 103 (1999) 7743–7746.
[14] C.D. Liang, K.L. Hong, G.A. Guiochon, J.W. Mays, S. Dai, Angew. Chem. Int. 43
(2004) 5785–5789.
[32] M.L. Ferreira, M. Volpe, J. Mol. Catal. A Chem. 164 (2000) 281–290.
[33] M.S. Kane, L.C. Kao, R.K. Mariwala, D.F. Hilscher, H.C. Foley, Ind. Eng. Chem. Res.
35 (1996) 3319–3331.
[34] M.F.R. Pereira, J.J.M. Órfão, J.L. Figueiredo, Appl. Catal. A 218 (2001) 307–318.
[35] D.S. Su, J.J. Delgado, X. Liu, D. Wang, R. Schlögl, L.F. Wang, Z. Zhang, Z.C. Shan,
F.S. Xiao, Chem. Asian J. 4 (2009) 1108–1113.
[15] S. Tanaka, N. Nishiyama, Y. Egshira, K. Ueyama, Chem. Commun. (2005)
2125–2127.
[16] Y. Meng, D. Gu, F. Zhang, Y. Shi, H. Yang, Z. Li, C. Yu, B. Tu, D. Zhao, Angew. Chem.
Int. 44 (2005) 7053–7058.
[17] F. Zhang, Y. Meng, D. Gu, Y. Yan, C. Yu, B. Tu, D. Zhao, J. Am. Chem. Soc. 127
(2005) 13508–13509.
[36] U. Zielke, K.J. Huttinger, W.P. Hoffman, Carbon 34 (1996) 983–998.
[37] B. Marchon, J. Carrazza, H. Heinemann, G.A. Somorjai, Carbon 26 (1988)
507–514.
[38] Y. Xie, P.M.A. Sherwood, Chem. Mater. 2 (1990) 293–299.
[39] H.F. Gorgulho, J.P. Mesquita, F. Gonc´alves, M.F.R. Pereira, J.L. Figueiredo, Carbon
46 (2008) 1544–1555.
[18] Y. Huang, H. Cai, T. Yu, F. Zhang, F. Zhang, Y. Meng, D. Gu, Y. Wan, X. Sun, B. Tu,
D. Zhao, Angew. Chem. Int. 46 (2007) 1089–1093.
[19] L. Liu, F.Y. Wang, G.S. Shao, Z.Y. Yuan, Carbon 48 (2010) 2089–2099.
[20] A.H. Lu, B. Spliethoff, F. Schüth, Chem. Mater. 20 (2008) 5314–5319.
[21] D.Y. Zhao, Q.S. Huo, J.L. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem. Soc. 120
(1998) 6024–6036.
[40] J.L. Figueiredo, M.F.R. Pereira, Catal. Today 150 (2010) 2–7.
[41] J. Zhang, D.S. Su, R. Blume, R. Schlögl, R. Wang, X. Yang, Angew. Chem. Int. Ed.
49 (2010) 8640–8644.
[42] X. Liu, B. Frank, W. Zhang, T.P. Cotter, R. Schlögl, D.S. Su, Angew. Chem. Int. Ed.
50 (2011) 3318–3322.
[43] L.E. Cadús, L.A. Arrua, O.F. Gorriz, J.B. Rivarola, Ind. Eng. Chem. Res. 27 (1988)
2241–2246.
[22] M. Chen, J. Xu, Y. Cao, H.Y. He, K.N. Fan, J.H. Zhuang, J. Catal. 272 (2010) 101–108.