Selective oxidation of p-chlorotoluene to p-chlorobenzaldehyde over metal-modified OMS-2 molecular sieves

Article abstract of DOI:10.1016/j.molcata.2016.09.038

A series of manganese oxide octahedral molecular sieve (OMS-2) doped with Co, V, and Ce (Me) with molar ratio Me/Mn?=?0.04 and 0.12 were prepared via a one-step reflux method, and were characterized by XRD, SEM, IR, BET, ICP, XPS, and TG techniques. The OMS-2 materials doped with Me having Me/Mn?=?x are denoted as Me-M(x). It was found that Ce mainly enters the tunnel structure of OMS-2 instead of K, Co mainly substitutes for Mn in the framework, and V is likely to substitution into both the Mn and K in the cryptomelane tunnel structure. The length of OMS-2 rods decreases with the decline of K⁺ mole fraction in the OMS-2 tunnels. Doping V and Ce markedly decreases the crystallization of OMS-2. Ce-M(0.12) shows a specific surface area (142?m²?g^?1) roughly double that of OMS-2 (69?m²?g^?1). All the Me-M(x) materials were tested as catalysts for the oxidation of p-chlorotoluene to p-chlorobenzaldehyde with molecular oxygen, and it is Ce-M(0.12) that shows the highest catalytic activity. The excellent performance is attributed to the large specific surface area and good mobility of oxygen species of the Ce-M(0.12) material.

Full text of DOI:10.1016/j.molcata.2016.09.038

Journal of Molecular Catalysis A: Chemical 425 (2016) 110–115
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Selective oxidation of p-chlorotoluene to p-chlorobenzaldehyde over
metal-modified OMS-2 molecular sieves
Jun Xiea, Lang Chena, Wei-Fang Zhoua, Chak-Tong Aua,b, Shuang-Feng Yina,∗
a State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan Provincial Key Laboratory for Cost-effective Utilization of Fossil Fuel Aimed at
Reducing Carbon-dioxide Emissions, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, Hunan, China
b College of Chemistry and Chemical Engineering, Hunan Institute of Engineering, Xiangtan 411104, Hunan, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 July 2016
Received in revised form
27 September 2016
Accepted 30 September 2016
Available online 30 September 2016
A series of manganese oxide octahedral molecular sieve (OMS-2) doped with Co, V, and Ce (Me) with
molar ratio Me/Mn = 0.04 and 0.12 were prepared via a one-step reflux method, and were character-
ized by XRD, SEM, IR, BET, ICP, XPS, and TG techniques. The OMS-2 materials doped with Me having
Me/Mn = x are denoted as Me-M(x). It was found that Ce mainly enters the tunnel structure of OMS-2
instead of K, Co mainly substitutes for Mn in the framework, and V is likely to substitution into both the
Mn and K in the cryptomelane tunnel structure. The length of OMS-2 rods decreases with the decline of
K+ mole fraction in the OMS-2 tunnels. Doping V and Ce markedly decreases the crystallization of OMS-2.
Ce-M(0.12) shows a specific surface area (142 m2 g−1) roughly double that of OMS-2 (69 m2 g−1). All the
Me-M(x) materials were tested as catalysts for the oxidation of p-chlorotoluene to p-chlorobenzaldehyde
with molecular oxygen, and it is Ce-M(0.12) that shows the highest catalytic activity. The excellent per-
formance is attributed to the large specific surface area and good mobility of oxygen species of the
Ce-M(0.12) material.
Keywords:
p-Chlorotoluene
p-Chlorobenzaldehyde
Selective oxidation
OMS-2
Cerium
© 2016 Published by Elsevier B.V.
1. Introduction
impregnation, reflux, and hydrothermal treatment [7–11]. Depend-
ing on the doping strategy, the metal ions can either end up on the
p-Chlorobenzaldehyde (PCB) is an important intermediate for
the production of dyes, pharmaceutical drugs, optical brighteners
and agricultural chemicals [1]. For industrial PCB production, sol-
uble acetates of transition metals are used as catalysts but some
of the processes are expensive and polluting [2]. With the decline
of traditional industries and for the protection of environment,
efforts were put in to fabricate solid catalysts capable of producing
aromatic aldehydes through selective oxidation of aromatic hydro-
carbons using molecular oxygen or hydrogen peroxide as oxidant.
However, both conversion and selectivity are not satisfactory [3,4].
Cryptomelane-type octahedral manganese oxide molecular
surface, in the framework or in the tunnels of OMS-2. Also, with
the metal ions incorporated in the framework or tunnel structure
of OMS-2, there is the creation of defects and hence increases num-
ber of active sites [12,13]. It is known that the doping of OMS-2
with metal ions can result in the generation of materials that are
different in nanostructures, but in-depth investigation on the fac-
tors affecting the morphology and activity-structure relationship
in terms of catalytic performance are lacking [12–14]. Previously,
we synthesized a series of OMS-2 materials for the generation of
PCB by means of p-chlorotoluene (PCT) oxidation [15–17]. It is reck-
oned that the catalytic performance of OMS-2 is dependent on its
preparation method, composition and morphology. To elucidate
the activity-structure relationship, we doped OMS-2 with a vari-
ety of metal ions, and adopted PCT oxidation for PCB generation as
model reaction.
After considering the size, valence, and reducibility of a large
number of metal ions, we adopted Co, V and Ce ions (Me) for the
doping of OMS-2, with the Me/Mn molar ratio = 0.04 or 0.12. The
materials doped with Me having Me/Mn = x are denoted hereinafter
as Me-M(x). The results show that the composition, crystallinity,
morphology and stability of Me-M(x) are greatly influenced by the
valence, amount, and location of the Me ions. It was found that
sieves (OMS-2) with mixed-valence manganese (Mn3+ and Mn4+
)
and a well-defined 2 × 2 tunnel structure is catalytically efficient
for many oxidation processes [5,6]. The stability and charge bal-
ance of OMS-2 is maintained by having potassium ions in the
OMS-2 tunnels. For further improvement of catalytic activity, OMS-
2 is commonly doped with foreign metal ions (e.g. Cu2+, Co2+
,
Al3+, Fe3+, Ce4+, Zr4+ or V5+) using methods such as ball milling,
∗
Corresponding author.
E-mail addresses: sf yin@hnu.edu.cn, yinsf73@163.com (S.-F. Yin).
http://dx.doi.org/10.1016/j.molcata.2016.09.038
1381-1169/© 2016 Published by Elsevier B.V.

J. Xie et al. / Journal of Molecular Catalysis A: Chemical 425 (2016) 110–115
111
Ce-M(0.12) is highly effective for the oxidation of PCT to PCB;
while the doping of OMS-2 with Co ions worsens the catalytic per-
formance of OMS-2. Based on the results of characterization and
catalytic performance, new insights into the effect of Me doping on
the catalytic activity of OMS-2 are acquired.
2. Experimental
2.1. Catalyst preparation
Me-M(x) was synthesized using a reflux method [15]. Typically,
a KMnO4 solution (6.5 g in 114 mL of distilled water) was added to
a mixture of MnSO4·H2O (9.9 g in 34 mL distilled water) and con-
centrated HNO3 (3.4 mL). Then, a designated amount of Co(NO3)2,
NH4VO3 or Ce(NO3)3 was added. The as-resulted material was fil-
tered out, washed, dried and then calcined at 400 ◦C for 4 h.
Fig. 1. X-ray diffraction patterns of OMS-2 and Me-M(x).
2.2. Catalyst characterization
of impurity atoms in the structure of molecular sieve. The presence
of amorphous metal oxide in Me-M (x) can be detected by infrared
spectroscopy [20]. As depicted in Fig. 2, the spectrum of OMS-2
shows four bands around 714, 582, 523 and 467 cm−1 characteristic
of MnO6 octahedral framework due to Mn-O vibrations [9]. There is
only insignificant change of peak intensity in the case of Co doping,
but with the doping of V or Ce, the 582 cm−1 band slightly increases
while the 467 and 714 cm−1 band obviously decrease in intensity.
The variation in the FTIR spectra indicates that there is entrance
of cerium or vanadium into the framework of OMS-2, resulting in
the new structure vibration. In addition, the band at ca. 980 cm−1
in the V-M(x) case is attributable to vanadium oxide [20,21]. The
dominant absorption peak at 1633 cm−1 is due to H2O in the OMS-2
tunnels [22].
Fig. 3 shows the representative SEM images of OMS-2 and Me-
M(x). The OMS-2 sample has a fibrous rod-like morphology, having
a rod length of 1-1.5 ␮m (Fig. 3g). The surface morphology of OMS-2
remains unchanged after the addition of Co (Figs. 3a and b). How-
ever, upon the addition of vanadium or cerium, there is clear change
of OMS-2 morphology. For example, the SEM images of V-M(0.04)
shows the presence of short rod-like entities around 200 nm in
length. With increase of vanadium amount, rods shorter in length
are randomly accumulated in the form of bulk assembly. Such a
phenomenon is even more obvious with Ce doping: the length of
OMS-2 rod-like entities decreases to about 50 nm in the Ce-M(0.04)
case, and clusters of the kind are detected (Fig. 3e). With further
increase of Ce content, microspheres with relatively flat surface are
Powder X-ray diffraction (XRD) scanning was conducted on
a Brüker D8 Advance diffractometer using Cu K␣ radiation. The
data were recorded at a scan rate of 0.02◦ (2␪) s−1 in the 10−80◦
range. In the form of KBr thin pellet, the catalyst was studied
by Fourier transform infrared (FTIR) spectroscopy (IR Affinity-1
spectrometer). Scanning electron microscopy (SEM) images were
taken on a Hitachi S-4800 emission scanning microscope with a
Schottky Emitter at an accelerating voltage of 5 kV and a beam
current of 1 mA. The Brunauer-Emmett-Teller (BET) specific sur-
face areas were measured on a Tristar 3000 instrument whereas
element analysis was carried out using ICP-AES (IRIS1000). X-Ray
photoelectron spectroscopy (XPS) analysis was conducted over a
K-Alpha 1063 (Thermo Fisher Scientific, USA) spectrometer using
Al K␣ radiation (1486.6 eV). The C 1 s signal of contaminant carbon
(BE = 284.6 eV) was taken as a reference for BE calibration. Thermal
stability of catalysts was studied by thermogravimetric analysis
(TGA, PerkinElmer Diamond TG/DTA instrument) with ca. 10 mg
of sample being heated from 30 to 800 ◦C (ramp rate = 10 ◦C/min)
under a N2 atmosphere.
2.3. Catalyst evaluation
All experiments were carried out in a three-necked round-
bottom flask equipped with a reflux condenser. The detailed
procedures for catalyst evaluation were reported elsewhere [18].
3. Results and discussion
3.1. Characterization results
The XRD patterns of OMS-2 and Me-M(x) are shown in Fig. 1. The
main diffraction peaks of the three are at 2␪ = 12.7◦, 17.9◦, 28.7◦,
37.4◦, 42◦, 50◦ and 60.2◦ that are typical of cryptomelane (JCPDS
29-1020). As displayed in Fig. 1, no additional peaks assignable to
segregated crystalline phases of Co, V or Ce oxides are observed,
suggesting that the Me-M(x) materials are phase pure. There is
no obvious change of the OMS-2 pattern with the doping of Co.
However, the doping of V or Ce results in marked decrease of peak
intensity and broadening of peak width, implying decrease in both
grain size and crystallinity of OMS-2 [19]. In addition, the XRD
pattern of used (four cycles) Ce-M (0.12) shows no significant dif-
ference in comparison with that of the fresh one. It is deduced that
there is no change of catalyst structure during the reaction.
Compared with the X-ray diffraction technique, the infrared
spectrum method is more sensitive to impurity phase in the struc-
ture, and can be used to determine whether there is the presence
Fig. 2. FT-IR spectra of OMS-2 and Me-M(x).

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J. Xie et al. / Journal of Molecular Catalysis A: Chemical 425 (2016) 110–115
200
OMS-2
Co-M(0.12)
V-M(0.12)
Ce-M(0.12)
150
100
50
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (p/p0)
Fig. 4. N2 adsorption-desorption isotherm of OMS-2 and Me-M(x).
Table 2
XPS and ICP results of OMS-2 and Me-M(0.12).
samples
Me/Mn (mol.)
ICP
OII/OI
XPS
OMS-2
0
0
0.232
0.163
0.132
0.401
Co-M(0.12)
V-M(0.12)
Ce-M(0.12)
0.052
0.116
0.058
0.062
0.192
0.020
there is partial substitution of framework Mn as well as displace-
ment of tunnel K by V. It is noted that the shortening of rod length
of the Me-M(x) materials goes together with the decrease in mole
fraction of potassium ions.
Fig. 4 shows the nitrogen adsorption-desorption isotherms
of OMS-2 and Me-M(x), and the corresponding specific sur-
face areas are listed in Table 1. It is observed that Ce-M(0.12)
exhibits type IV isotherms, indicative of a solid mesoporous
structure. However, the others show type II isotherms with
Fig. 3. SEM images of (a) Co-M(0.04), (b) Co-M(0.12), (c) V-M(0.04), (d) V-M(0.12),
(e) Ce-M(0.04), (f) Ce-M(0.12), (g) OMS-2 and (h) Used (four cycles) Ce-M(0.12).
a
hysteresis loop of type H3, which is usually associated
Table 1
with an assembly of rod-like fibers with narrow slits that
are porous in structure. The BET surface areas follow the
order of Co-M(0.12) (59 m2g−1) < Co-M(0.04) (67 m2g−1) < OMS-2
(69 m2g−1) < V-M(0.04) (70 m2g−1) < V-M(0.12) (71 m2g−1) < Ce-
M(0.04) (80 m2g−1) < Ce-M(0.12) (142 m2g−1). One can see that it
is only through the doping of Ce that there is significant increase of
specific surface area. The increase can be attributed the assembly
of microspheres generated in the case of Ce-M(0.12). It is generally
accepted that an increase of specific surface area is beneficial for
the enhancement of catalytic reactivity.
Surface area and bulk composition estimated by ICP analysis.
Sample
BET surface area (m2/g) Mole fraction (%)
Mn
Me/Mn (mol.)
K
Me
OMS-2
69
67
59
73
76
9.080 90.920 0.000
8.770 88.560 2.670
8.620 86.900 4.480
9.020 87.580 3.400
4.520 85.560 9.920
7.140 90.500 2.360
1.750 92.840 5.410
0.000
0.030
0.052
0.039
0.116
0.026
0.058
Co-M(0.04)
Co-M(0.12)
V-M(0.04)
V-M(0.12)
Ce-M(0.04)
Ce-M(0.12)
80
142
Surface elemental analysis was carried out by means of XPS
(Fig. 5) and the results are summarized in Table 2. It was reported
that manganese atoms of mixed valence are situated in the octa-
hedral sites of cryptomelane [23]. The Mn 2p peaks of Mn3+ and
Mn4+ are at 641.9 and 642.4 eV (binding energy), respectively. The
co-existence of various oxidation states of Mn in OMS-2 is essential
for electron transfer [16]. To determine the distribution of metals,
we compared the surface and bulk Me/Mn atomic ratios of the sam-
ples. As shown in Table 1, the vanadium content of V-M(0.12) on
the surface (V/Mn atomic ratio = 0.192) is much higher than that
of the bulk (V/Mn atomic ratio = 0.116), indicating enrichment of
V on the surface. Nevertheless, the surface Ce/Mn atomic ratios of
Ce-M(0.12) is roughly one third that of the bulk value. The results
confirm that the doped Ce mainly resides in the tunnel structure of
OMS-2, replacing K as a result. On the other hand, the distribution of
cobalt in Co-M(0.12) is relatively uniform. The O1 s profiles of OMS-
2 and Me-M(0.12) can be fitted with two components (Fig. 5B), viz.
formed (Fig. 3f). Furthermore, there is only insignificant change of
catalyst morphology after four cycles of reaction (Fig. 3h).
In order to explore the reasons for the difference in morphology,
the compositions of the Me-M(x) materials were analyzed and the
results are shown in Table 1. In the preparation of Co-M(x), there is
almost no loss of Co. However, in the preparation of Ce-M(x) and V-
M(x), there are losses of Ce and V, especially when it is an attempt
of higher doping. In the Co-M(0.04) case, the introduction of Co
results in decline of Mn but K stays constant, indicating the partial
substitution of framework Mn by Co and insignificant replacement
of K in the tunnels by Co. In contrast, the K molar ratio of Ce-M(0.12)
is significantly lower than that of OMS-2, suggesting that there is
significant replacement of K by Ce. Although the amounts of Ce and
V retained in the catalysts are rather similar, there is drastic dif-
ference in terms of catalyst composition. In the case of V doping,

J. Xie et al. / Journal of Molecular Catalysis A: Chemical 425 (2016) 110–115
113
OI
(A)
Mn 2p
(B)
Mn+3
Mn+4
O1s
OII
Ce-M(0.12)
Ce-M(0.12)
V-M(0.12)
V-M(0.12)
Co-M(0.12)
Co-M(0.12)
OMS-2
OMS-2
536
534
532
530
528
660
655
650
645
640
Binding Energy (eV)
Binding Energy (eV)
Fig. 5. XPS spectra (A) Mn 2p and (B) O 1s of OMS-2 and Me-M(0.12).
99
96
93
90
87
99
(A)
(B)
96
OMS-2
Co-M(0.04)
Co-M(0.12)
93
90
87
OMS-2
Co-M(0.12)
V-M(0.12)
Ce-M(0.12)
100
200
300
400
500
600
700
800
100
200
300
400
500
600
700
800
Temperature (oC)
Temperature (oC)
99
96
93
90
87
99
96
93
90
87
(C)
(D)
OMS-2
V-M(0.04)
V-M(0.12)
OMS-2
Ce-M(0.04)
Ce-M(0.12)
100
200
300
400
500
600
700
800
100
200
300
400
500
600
700
800
Temperature (oC)
Temperature (oC)
Fig. 6. Thermogravimetric analysis of OMS-2 and Me-M(x) materials.
OI and OII that are assignable to surface lattice oxygen (ca. 529.8 eV)
and surface adsorbed oxygen (ca. 531.5 eV), respectively [24]. The
OII/OI ratio of OMS-2, Co-M(0.12), V-M(0.12) and Ce-M(0.12) is
0.232, 0.163, 0.132, and 0.401, respectively. It is known that the
OII species show higher mobility than the OI species, and plays a
more important role in catalytic oxidation reactions, especially at
low temperatures [10]. Obviously, among the prepared catalysts,
Ce-M(0.12) is the richest in terms of surface OII species.
The catalysts were subject to thermogravimetric analysis
(Fig. 6). It is generally accepted that weight losses of this kind of
materials in the 30–800 ◦C range can be divided into four cate-
gories: (I) 30–200 ◦C ascribable to desorption of physisorbed water,
(II) 200–400 ◦C attributable to desorption of chemisorbed water
and oxygen, (III) 400–650 ◦C ascribable to release of lattice oxy-
gen in the “MnO2 → Mn2O3” process, and (IV) above 650 ◦C due to
the evolution of O2 in the “Mn2O3 → Mn3O4” process [3]. Clearly,

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J. Xie et al. / Journal of Molecular Catalysis A: Chemical 425 (2016) 110–115
100
80
60
40
20
0
95
OMS-2
Co-M(0.04)
Co-M(0.12)
V-M(0.04)
V-M(0.12)
Ce-M(0.04)
Ce-M(0.12)
90
85
80
OMS-2
Co-M(0.04)
Co-M(0.12)
V-M(0.04)
V-M(0.12)
Ce-M(0.04)
Ce-M(0.12)
75
70
65
2
4
6
10
Reaction time (h) 8
2
4
6
10
Reaction time (h) 8
Fig. 7. Effect of reaction time on p-chlorotoluene oxidation.
(reaction conditions: catalyst 50 mg, p-chlorotoluene 1 mL, solvent 10 mL, HBr (40 wt.%) 0.02 g, H2O 2 g, oxygen flow rate 50 mL/min, temperature 100 ◦C).
all of the catalysts have plenty of lattice oxygen species that would
become mobile upon thermal excitation. As shown in Fig. 6A, the
weight of Ce-M(0.12) continuous decline, nevertheless, the weight
of V-M(0.12) and Co-M(0.12) have a significant decline at around
400 ◦C and 500 ◦C respectively. The Co-M(x) shows a profile almost
the same as that of OMS-2. This is probably because the size of
manganese ions (67.0-78.5 pm) is similar to that of cobalt ions
(68.5-79.0 pm). The low thermal stability is possibly related to the
lattice defects created due to the reduced presence of potassium
required to maintain the stability and charge balance of OMS-
2. It is known that a mismatch of crystal radii would result in
structural/lattice constraints [20]. Earlier studies showed that the
tetragonal geometry of cryptomelane distorts to monoclinic phase
when the ratio of lattice Mn ionic radius to tunnel cationic radius
exceeds 0.48 [25]. The replacement of K+ by the dopant ions of much
smaller radius puts strain on the lattice, which in turn strains the
Mn-O bonds [26]. Consequently, the anionic oxygen becomes more
activity.
surface area. The results indicate that the specific surface area of
catalysts is only one of the essential factors that govern the reac-
tivity of the catalysts.
Taking the XPS, ICP and TG results into consideration, the activ-
ity for liquid-phase partial oxidation of PCT can be correlated to the
degree of mobility of oxygen species in the catalysts. With mobil-
ity higher than that of OI species, the OII species play an important
role in catalytic oxidation reactions at low temperatures [9]. Ce-
M(0.12) is rich in surface OII species, while the doping of V and Co
causes reduction of OII species on the surface. According to the FT-
IR, XPS and ICP results, the decline of OII species in the V-M(0.12)
cases is probably due to the accumulation of V oxides on the sur-
face. According to the results of TG analysis, the Ce-M(0.12) catalyst
appears to be thermally the least stable among the prepared cata-
lysts (see TGA profiles, Fig. 6). Yang et al. reported that in terms of
selective oxidation, there is an increase in OMS-2 catalytic activity
with decrease of lattice stability [29]. Wang and Li demonstrated
that the catalysts with weaker Mn-O bonds are usually higher in
lattice defects and labile lattice oxygen, and exhibit better perfor-
mance [30]. Therefore, it is reasonable that V-M(0.12) is higher than
V-M(0.04) in activity.
3.2. Catalytic performance
The conversion of PCT to PCB over the OMS-2 and Me-M(x)
catalysts as a function of reaction time is shown in Fig. 7. Under
the adopted reaction conditions [27], PCT conversion increases
with reaction time, and after 10 h, the conversion of PCT is 93.5%
and selectivity to PCB is 76.1% over the Ce-M(0.12) catalyst. Over
OMS-2, PCT conversion and PCB selectivity are 83.7% and 73.3%,
respectively. The catalytic performance increases in the order
of Co-M(0.12) < OMS–2 < Co-M(0.04) < V-M(0.04) < V-M(0.12) < Ce-
M(0.04) < Ce-M(0.12). As discussed in detail in our previous work,
PCT oxidation over OMS-2 catalysts proceeds according to a Mars-
van Krevelen mechanism [15]. According to this mechanism, lattice
oxygen of OMS-2 participates in the oxidation reaction, and can be
replenished by fluid-phase oxygen. At the beginning the role of
Mn(IV) ions is to convert bromine ions to bromine radicals that
initiate the PCT oxidation reaction.
In many cases of using transition metal oxides as catalysts, a
higher surface area means better catalytic activity. Over OMS-2
synthesized with alkali-metal cations, Malinger et al. also observed
such a relationship in the oxidation of cyclohexanol [28]. In the
present study, the order of PCT conversion coincides well with
the sequence of BET surface areas. However, at similar levels
of specific surface area, such as V-M(0.04) (70 m2 g−1) and V-
M(0.12) (71 m2 g−1), there is significant difference in catalytic
activity between the two. In another case, V-M(0.12) and Ce-
M(0.04) (80 m2 g−1) are similar in activity but different in specific
3.3. Catalyst recyclability
The recyclability of the Ce-M(0.12) catalyst was tested. After
each run, the catalyst was filtered out and washed several times
Conv.
100
Sel.
80
60
40
20
0
1
2
3
4
Run
Fig. 8. Recycling of Ce-M(0.12) in the oxidation of p-chlorotoluene.
(reaction conditions: catalyst 50 mg, p-chlorotoluene 1 mL, solvent 10 mL, HBr
(40 wt.%) 0.02 g, H2O 2 g, oxygen flow rate 50 mL/min, temperature 100 ◦C).

J. Xie et al. / Journal of Molecular Catalysis A: Chemical 425 (2016) 110–115
115
with alcohol before being dried at 110 ◦C overnight. Across the four
runs, there is no obvious decrease of p-chlorotoluene conversion
and p-chlorobenzaldehyde selectivity (Fig. 8). The XRD pattern and
SEM of the used catalysts indicate that the structure and morphol-
ogy of the catalyst are preserved during the four cycles of oxidation
reaction.
[2] A.J. Hu, C.X. Lü, B.D. Li, T. Huo, Ind. Eng. Chem. Res. 45 (2006) 5688–5692.
[3] F.M. Bautista, D. Luna, J. Luque, J.M. Marinas, J.F. Sánchez-Royo, Appl. Catal. A
352 (2009) 251–258.
[4] J.Q. Wang, H. Fang, Y. Li, J.J. Li, Z.Y. Yan, J. Mol. Catal. A 250 (2006) 75–79.
[5] A.R. Gandhe, J.S. Rebello, J.L. Figueiredo, J.B. Fernandes, Appl. Catal. B 72
(2007) 129–135.
[6] Y.C. Son, V.D. Makwana, A.R. Howell, S.L. Suib, Angew. Chem. 113 (2001)
4410–4413.
[7] X. Chen, Y.F. Shen, S.L. Suib, C.L. O’Young, J. Catal. 197 (2001) 292–302.
[8] J.T. Hou, Y.Z. Li, M.Y. Mao, X.J. Zhao, Y.Z. Yue, Nanoscale 6 (2014)
15048–15058.
4. Conclusions
[9] Y.Z. Li, Z.Y. Fan, J.W. Shi, Z.Y. Liu, J.W. Zhou, W.F. Shangguan, Catal. Today 256
(2015) 178–185.
[10] M. Sun, L. Yu, F. Ye, G.Q. Diao, Q. Yu, Z.F. Hao, Y.Y. Zheng, L.X. Yuan, Chem. Eng.
J. 220 (2013) 320–327.
Manganese oxide octahedral molecular sieve (OMS-2) doped
with Co, V and Ce having Me/Mn = 0.04, 0.12 were prepared via a
one-step reflux method. It is observed that the Ce-M(0.12) catalyst
is the most active while the Co-M(0.12) is the most inferior. Dop-
ing Ce to OMS-2 significantly increases the BET surface area from
69 m2g−1 for OMS-2 to 142 m2g−1 for Ce-M(0.12). The XPS and TG
results confirm the presence of Mn3+ and Mn4+ in the Me-M(x) cat-
alysts. The Ce-M(0.12) catalyst is high in oxygen mobility as well as
in concentration of reactive oxygen species. It is deduced that the
enhanced catalytic activity of Ce-M(0.12) is a combined outcome of
the high specific surface area and good mobility of oxygen species.
[11] G.D. Yadav, R.V. Sharma, Appl. Catal. B 147 (2014) 293–301.
[12] H. Sun, S. Chen, P. Wang, X. Quan, Chem. Eng. J. 178 (2011) 191–196.
[13] L.L. Zhang, J.J. Tu, L. Lyu, C. Hu, Appl. Catal. B 181 (2016) 561–569.
[14] M. Abecassis-Wolfovich, R. Jothiramalingam, M.V. Landau, M. Herskowitz, B.
Viswanathan, T.K. Varadarajan, Appl. Catal. B 59 (2005) 91–98.
[15] Y.Q. Deng, T. Zhang, C.T. Au, S.F. Yin, Appl. Catal. A 467 (2013) 117–123.
[16] Y.Q. Deng, T. Zhang, C.T. Au, S.F. Yin, Catal. Commun. 43 (2014) 126–130.
[17] T. Zhang, Y.Q. Deng, W.F. Zhou, C.T. Au, S.F. Yin, Chem. Eng. J. 240 (2014)
509–515.
[18] W.F. Zhou, L. Chen, J. Xie, C.T. Au, S.F. Yin, RSC Adv. 5 (2015) 74162–74169.
[19] M. Polverejan, J.C. Villegas, S.L. Suib, J. Am. Chem. Soc. 126 (2004) 7774–7775.
[20] C.K. King’ondu, N. Opembe, C.H. Chen, K. Ngala, H. Huang, A. Iyer, S.L. Suib,
Adv. Funct. Mater. 21 (2011) 312–323.
[21] A. Martin, U. Bentrup, G.U. Wolf, Appl. Catal. A 227 (2002) 131–142.
[22] G.H. Qiu, H. Huang, S. Dharmarathna, E. Benbow, L. Stafford, S.L. Suib, Chem.
Mater. 23 (2011) 3892–3901.
[23] X.S. Liu, Z.N. Jin, J.Q. Lu, X.X. Wang, M.F. Luo, Chem. Eng. J. 162 (2010) 151–157.
[24] X.F. Tang, J.H. Li, J.M. Hao, Catal. Commun. 11 (2010) 871–875.
[25] J.E. Post, R.B. Von Dreele, P.R. Buseck, Acta Crystallogr. B 38 (1982) 1056–1065.
[26] R. Kumar, L.J. Garces, Y.C. Son, S.L. Suib, R.E. Malz, J. Catal. 236 (2005) 387–391.
[27] G.C. Yin, G.Y. Cao, S.H. Fan, X.D. Hai, Appl. Catal. A 185 (1999) 277–281.
[28] K.A. Malinger, Y.S. Ding, S. Sithambaram, L. Espinal, S. Gomez, S.L. Suib, J.
Catal. 239 (2006) 290–298.
Acknowledgments
The project was financially supported by the National Natural
Science Foundation of China (Grant Nos. 21273067, 21476065),
Program for Changjiang Scholars and Innovative Research Team in
University (IRT1238), and the Fundamental Research Funds for the
Central Universities. C.T. Au thanks the Hunan University for an
adjunct professorship.
[29] X.J. Yang, J.Y. Han, Z.P. Du, H. Yuan, F. Jin, Y.X. Wu, Catal. Commun. 11 (2010)
643–646.
[30] R.H. Wang, J.H. Li, Environ. Sci. Technol. 44 (2010) 4282–4287.
References
[1] R.A. Sheldon, H. Van Bekkum, Fine Chemicals Through Heterogeneous
Catalysis, John Wiley & Sons, 2008.