Iron Oxide as a Promoter for Toluene Catalytic Oxidation Over Fe–Mn/γ-Al2O3 Catalysts

Article abstract of DOI:10.1007/s10562-019-02975-5

Abstract: Fe–Mn/γ-Al₂O₃ catalysts that prepared by the wet-impregnation method were used to degrade toluene, a VOCs model compound. The results indicated that the 10Fe–15Mn/γ-Al₂O₃ exhibited 95% of toluene conversion as well as 95% of CO₂ yield at 300?°C. The Fe–Mn/γ-Al₂O₃ showed a better toluene oxidation activity with respect to the Fe/γ-Al₂O₃ and Mn/γ-Al₂O₃. The introduction of Fe into the Mn/γ-Al₂O₃ resulted in higher surface area, higher Mn³⁺/(Mn³⁺+ Mn⁴⁺) ratio, lower reduction temperature, and homogenous distribution of Mn. Meanwhile, the co-exist of the Fe³⁺ and Mn³⁺ over the 10Fe–15Mn/γ-Al₂O₃ also favored for the oxygen transfer, which may enhance the catalytic oxidation performance. The initial toluene was adsorbed on surface of the catalysts and formed benzoyl oxide (C₆H₅–CH₂–O), and then the benzoyl oxide (C₆H₅–CH₂–O) was oxidized to benzaldehyde. Furthermore, the benzaldehyde was further oxidized to form benzoic acid that could be converted to CO₂ and H₂O. Graphic Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02975-5

Catalysis Letters
https://doi.org/10.1007/s10562-019-02975-5
Iron Oxide as a Promoter for Toluene Catalytic Oxidation Over Fe–Mn/
γ‑Al2O3 Catalysts
Linbo Qin1,2 · Xinming Huang1,2 · Bo Zhao1,2 · Yu Wang1,2 · Jun Han1,2
Received: 12 August 2019 / Accepted: 17 September 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Fe–Mn/γ-Al2O3 catalysts that prepared by the wet-impregnation method were used to degrade toluene, a VOCs model com-
pound. The results indicated that the 10Fe–15Mn/γ-Al2O3 exhibited 95% of toluene conversion as well as 95% of CO2 yield
at 300 °C. The Fe–Mn/γ-Al2O3 showed a better toluene oxidation activity with respect to the Fe/γ-Al2O3 and Mn/γ-Al2O3.
The introduction of Fe into the Mn/γ-Al2O3 resulted in higher surface area, higher Mn3+/(Mn3++Mn4+) ratio, lower reduction
temperature, and homogenous distribution of Mn. Meanwhile, the co-exist of the Fe3+ and Mn3+ over the 10Fe–15Mn/γ-
Al2O3 also favored for the oxygen transfer, which may enhance the catalytic oxidation performance. The initial toluene was
adsorbed on surface of the catalysts and formed benzoyl oxide (C6H5–CH2–O), and then the benzoyl oxide (C6H5–CH2–O)
was oxidized to benzaldehyde. Furthermore, the benzaldehyde was further oxidized to form benzoic acid that could be
converted to CO2 and H2O.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02975-5) contains
supplementary material, which is available to authorized users.
* Bo Zhao
zhaobo87@wust.edu.cn
* Jun Han
hanjun@wust.edu.cn
1
Hubei Key Laboratory for Efcient Utilization
and Agglomeration of Metallurgic Mineral Resources,
Wuhan University of Science and Technology,
Wuhan 430081, People’s Republic of China
2
Hubei Provincial Industrial Safety Engineering
Technology Research Center, Wuhan University of Science
and Technology, Wuhan 430081, People’s Republic of China
Vol.:(0123456789)
1 3

L. Qin et al.
Graphic Abstract
1 3

Iron Oxide as a Promoter for Toluene Catalytic Oxidation Over Fe–Mn/γ-Al2O3 Catalysts
Keywords Fe–Mn/γ-Al2O3 · In-situ FTIR · Iron oxide ·
Co–Mn oxides under the conditions of 20,000 ml g−1 h−1
Toluene oxidation
and 1500 ppm of benzene. Wang [24] found that the layered
Cu–Mn oxide exhibited good catalytic activity for VOCs
oxidation due to the formation of Cu2+–O2−–Mn4+, result-
ing in more active oxygen and vacancies species in Cu–Mn
oxide, which was also proved by Hu [25]. Fe-based oxides
used as a promoter to synthetize multi-metal catalysts have
received widely attention due to its low cost, good stability
and higher moisture toleration [26]. Baldi [27] also observed
a similar catalytic performance of Mn2O3–Fe2O3 prepared
by co-precipitation with respect to Mn2O3. Durán [28] found
that the mechanical mixture of Mn2O3 and Fe2O3 exhib-
ited a catalytic activity similar to those of Mn2O3, but the
catalytic oxidation activities of representative VOCs over
Fe–Mn mixed oxides prepared using the citrate method
was higher than that of the Fe2O3 and Mn2O3, indicating
that synergy efects between Fe and Mn were beneftable
for enhancing the catalytic performance. Quiroga [29] also
found that Fe–Mn mixed oxides catalyst synthetized by
mechano-chemical reaction exhibits higher n-hexane oxi-
dation activity compared to Fe2O3 and MnOx. Chen [17]
reported that Fe–Mn binary oxides synthetized via hydroly-
sis driving redox method shows higher toluene oxidation
activity compared to MnOx. However, the low cost meth-
ods for preparing Fe–Mn oxides catalyst (mainly include
mechanical mixture, impregnation, and co-precipitation) are
difcult to obtain homogeneous oxide, which results in lower
catalytic oxidation performance for VOCs [30]. Meanwhile,
these Fe–Mn oxides catalysts prepared by Durán [28], Qui-
roga [29] and Chen [17] showed deactivation towards VOC
degradation.
1 Introduction
Volatile organic compounds (VOCs) are regarded as a con-
tributor of photochemical smog, global warming, and ozone
depletion [1–3]. Over 300 VOCs has been recognized as the
major contributors to air pollution by U.S. Environmental
Protection Agency. Among them, the aromatic VOCs includ-
ing benzene, toluene, o-xylene, chlorobenzene and etc., with
high toxicity to human health and “carcinogenic-mutagenic-
teratogenic” efect, mainly originate from industrial source
[4]. It was estimated that China emits 31.12 million tons of
VOCs in 2015 [5]. The industrial sources VOCs contribute
to over 50% of the total emissions [6–8]. In order to reduce
VOCs emissions, VOCs has been regarded as one of the
main air pollutants by Chinese government in 2010. In 2015,
it was proposed that reducing 10% of VOCs emissions from
the typical regions and industries compared to those in 2015
during the Chinese 13th Five-Year Plan.
At present, several technologies including adsorption [9],
catalytic oxidation [10], thermal oxidation [11–14], plasma
oxidation [15], photocatalysis [16], and biotechnology
[5] are used to control the VOCs emission. Among these
technologies, catalytic oxidation is regarded as one of the
most efective method for removing VOCs with producing
CO2 and H2O at 250–550 °C [17]. In catalytic reaction sys-
tem, there are two types of catalysts that are widely used
for VOCs degradation. One is supported precious metals
catalysts such as Au, Ag, and Pt, which shows higher low-
temperature catalytic performance, while their applications
are limited due to its high cost, and easily poisoning [18].
Another is the transition-metal oxide catalysts, including Fe,
Mn, Cu, Ni, and Co, that have advantages of low cost and
easy availability compared to the supported precious metal
[19]. Manganese oxide (MnOx) is one of the transition metal
oxides that widely used for catalytic oxidation of gaseous
pollutants (CO, NO and VOCs) since it is characterized with
varied valences of Mn (viz. Mn2+, Mn3+ and Mn4+), low
cost, and environmental friendliness [20]. Nevertheless, the
catalytic performance of the individual MnOx in terms of
stability and activity is not satisfed with the requirement for
aromatic VOCs degradation [21].
Previous investigations had reported that the metal
oxides loaded on supports shows higher catalytic activity
and homogenous distribution of active components than
the unsupported metal oxide catalyst due to the synergy
efects between supports and active component [31]. Metal
oxide loaded on supports such as α-Al2O3 and γ-Al2O3,
SiO2, TiO2, ZrO2, cordierite and attapulgite have been
received wide investigation [31–33]. Wang [34] found that
Cu–Mn/γ-Al2O3 showed a better toluene catalytic activity
than CuO–MnOx due to homogenous distributions of Mn
and Cu into the γ-Al2O3. Ma [35] reported that the Fe–Mn/
cordierite exhibited higher toluene catalytic activity com-
pared to the unsupported Fe–Mn mixed oxides. At present,
Fe–Mn/Al2O3 has been widely investigated for NO and mer-
cury oxidation since it is characterized with higher catalytic
activity, good stability and higher moisture toleration [36,
37]. However, Fe–Mn oxides loaded Al2O3 (Fe–Mn/Al2O3)
has not been developed for VOCs removal.
The introduction of Fe, Cu, Ce, and Co into Mn-based
oxides is one of the major methods for improving the
catalytic activities. Chen [4] reported that a homogenous
3MnOx–1CeOy (3Mn1Ce) prepared by hydrolysis driv-
ing redox method exhibits a higher toluene oxidation per-
formance compared to MnO2 and CeO2, which was also
proved by Du [22]. Zhang [23] claimed that 90% of ben-
zene conversion is obtained at 191 °C for the nanosheet
In this paper, a series of Fe–Mn/γ-Al2O3 catalysts are
synthetized using wet-impregnation method, and the cat-
alytic oxidation of toluene over the Fe–Mn/γ-Al2O3 cata-
lysts are also evaluated. Meanwhile, these catalysts are also
1 3

L. Qin et al.
characterized by means of the BET, XRD, XPS, H2-TPR,
and in situ FTIR.
and then cooled to 50 °C under Ar atmosphere. To evaluate
the efect of reaction temperature, the simulated gas contain-
ing about 400 mg m−3 toluene was introduced to the Harrick
reaction cell under a fow rate of 20 ml min−1 (Ar or Ar+O2),
and then the FTIR spectra were continuously recorded as the
reaction temperature was heated from 50 to 400 °C with the
heating rate of 10 °C min−1.
2 Experimental
2.1 Catalysts Preparation
A series of xFe–yMn/γ-Al2O3 catalysts were prepared
by the wet-impregnation method. In briefy, γ-aluminum
oxide (γ-Al2O3, 100–200 μm) was used as the support.
Iron (III) nitrate (Fe(NO3)3, 20 wt% aqueous solution) and
manganese(II) nitrate (Mn(NO3)2, 20 wt% aqueous solution)
were used as active components. γ-Al2O3 was added into the
solutions that prepared from the stoichiometric amount of
Fe(NO3)3, Mn(NO3)2 and double distilled water, and then
stirred at 30 °C for 6 h. Afterward, the samples were washed
and dried at 105 °C for 4 h, and then calcined at 400 °C for
4 h. These catalysts obtained from the wet-impregnation of
Fe(NO3)3 and Mn(NO3)2 with γ-Al2O3 support were denoted
as xFe–yMn/γ-Al2O3, where x and y represented the weight
percentage of Fe2O3 and MnO2 based on the γ-Al2O3 sup-
port, e.g. 10Fe–15Mn/γ-Al2O3.
2.4 Catalytic Test
The catalytic test was performed in a fxed reactor, which con-
sisted of a gas supply device, a reactor and gas measuring
system, as detail described in our previous paper [38, 39]. The
reactor had a length of 1000 mm and an internal diameter of
20 mm. The simulated gases were provided by gas cylinders
controlled by mass fow meters. The H2O vapor was provided
using a water saturator coupled with a U-type absorption tube,
and the toluene was supplied by an injection pump and an
evaporator (FD-PG, Suzhou, China). The simulated gas con-
tains 400 10 mg m−3 of toluene. The gas measuring system
consisted of a gas chromatography equipped with a fame
ionization detector (FID) and a thermal conductivity detector
(TCD) (GC, Agilent 7820A), and gas chromatography–mass
spectrometry (GC/MS, QP2010 SE). To evaluate the oxidation
activity of these catalysts at 100–400 °C, the catalytic oxida-
tion of toluene was tested in a fxed bed reactor packed with
4.0 g of catalysts (100–200 μm) under gas hourly space veloc-
ity (GHSV) range of 20,000 h−1. When the efects of diferent
GHSV and oxygen content were evaluated for the oxidation
activity of these catalysts, the fow rates of O2 and N2 were
adjusted to satisfy with the requirements of GHSV and O2 con-
tent. To investigate the efect of H2O on the oxidation activ-
ity of these catalysts, 10 vol% H2O was introduced into the
simulated gas. The composition of the outlet gas was on-line
monitored by the GC and GC/MS. The toluene conversion was
calculated by the diference of the toluene concentration. CO2
in the outlet gas was also detected by GC–TCD, and the rare
content of other byproducts in exhaust gas were also recorded
by the GC/MS. The toluene conversion and CO2 yields were
calculated according to the Eqs. (1) and (2):
2.2 Catalysts Characterization
In this study, an automated adsorption analyzer (BET,
Micromeritics ASAP 2020) was used to analyze the BET
surface, pore volume and pore size distribution of these
xFe–yMn/γ-Al2O3 catalysts. X-ray difractometer (XRD,
Rigaku Dmax/2400) was employed to characterize the
crystalline structures of these catalysts. X-ray photoelec-
tron spectroscopy (XPS, AXIS ULTRADLD) was used to
measure the compositions of the catalysts. Meanwhile, the
contents of Fe and Mn in these catalysts were also measured
by the inductively coupled plasma-mass spectrometry (ICP-
MS, ELAN DRC-e).
In addition, temperature-programmed reduction (H2-TPR)
were tested on a micromeritics Chem star™ (Quanta chrome
Instruments). The catalysts were frstly pretreated in argon
(Ar) atmosphere at 300 °C for 60 min, and then the tem-
perature was increased to 1000 °C under a heating rate of
10 °C min−1 with a fow rate of H2/Ar (H2/Ar ratio is 10:
90) of 20 ml min−1, and the H2 consumption is continuously
recorded.
CToluene − C
Toluene
out
in
XT =
× 100%
(1)
CToluene
in
CO2
C
out
XCO
=
× 100%
(
)
(2)
2.3 In Situ DRIFTS Test
2
Toluene
out
7 × CToluene − C
in
In-situ FTIR experiments were carried out on an FTIR spec-
trometer (FTIR, Bruker Tensor II) equipped with a Harrick
reaction cell under the wavenumber range of 4000–1000 cm−1.
Before the experiment, 20 mg catalyst loaded in Harrick reac-
tion cell was pretreated at 300 °C in a Ar atmosphere for 0.5 h
where XT was the toluene conversion (%); XCO was the CO2
2
yields (%); while CToluene and C
were the concentration
Toluene
out
in
CO2
of toluene in the inlet and outlet gas, respectively; C was
out
the concentration of CO2 in the outlet gas.
1 3

Iron Oxide as a Promoter for Toluene Catalytic Oxidation Over Fe–Mn/γ-Al2O3 Catalysts
3.1.2 XRD
3 Results and Discussion
3.1 Catalyst Characterization
3.1.1 BET
Figure 1 presented the crystalline structures of these cata-
lysts. There were several peaks corresponding to the γ-Al2O3
at 37.4°, 45.8°, 64.9°, and 66.9o observed on the surface of
these catalysis (JCPDS NO. 35-0121) [37]. Several difrac-
tion peaks located at 23.1°, 32.8°, 38.2°, 45.4°, 49.3°, 55.3°,
61.0°, 64.1° and 65.8° detected, which were attributed to
Mn2O3 (JCPDS NO. 89-4836), were gradually increased as
the weight fraction of Mn increase. Meanwhile, the char-
acteristic peaks (24.2°, 33.1°, 35.7°, 41.0°, 49.2°, 54.0°,
62.6°, 64.2°, and 71.9°) of α-Fe2O3 (JCPDS NO. 33-0664)
were also detected over the 10Fe/γ-Al2O3 and 10Fe–15Mn/γ-
Al2O3. Moreover, peaks located at 37.3°, 42.7°, and 56.7°
corresponding to MnO2 (JCPDS NO. 30-0820) were also
formed on the surface of the 10Fe–15Mn/γ-Al2O3, inferring
that the crystal structure of Mn-based oxide changed after
the Fe introduction. Compared with the 15Mn/γ-Al2O3, the
intensities of the Mn difraction peaks were decreased after
the Fe introduction, indicating that Fe and Mn species on the
The pore properties of these Fe–Mn/γ-Al2O3 catalysts were
summarized in Table 1, it can be seen that the pore prop-
erties of the γ-Al2O3 such as BET surface area, pore vol-
ume and pore diameter were in sequence as 136 9 m2 g−1,
0.194 0.016 cm3 g−1 and 56.75 1.23 nm. After doping
with Fe2O3 or MnO2, the BET surface areas of Mn/γ-Al2O3
or Fe/γ-Al2O3 catalysts were obviously reduced, while
the pore volume and pore diameter of the Mn/γ-Al2O3 or
Fe/γ-Al2O3 catalysts were slightly increased. As the weight
fraction of MnO2 was added from 0 to 20%, the BET sur-
face areas of xMn/γ-Al2O3 were gradually decreased from
136 9 to 88 3 m2 g−1. The pore volumes of the xMn/γ-
Al2O3 have the similar values at 0.224–0.225 cm3 g−1 when
the MnO2-doping was range of 3–10%, while the pore vol-
umes of the xMn/γ-Al2O3 were gradually decreased as the
the MnO2-doping was increased from 10 to 20%. As for the
pore diameter, the pore diameter of the xMn/γ-Al2O3 were
frstly increased and then decreased as the weight fraction
of MnO2 was added from 0 to 20%, and the maximum pore
diameter (76.78 nm) were obtained for the 15Mn/γ-Al2O3.
For the 10Fe–15Mn/γ-Al2O3 catalyst, the BET surface area
was increased, while the pore volume and pore diameter
was decreased compared with the 15Mn/γ-Al2O3 catalyst.
These results indicated that the role of Fe doping was likely
to enhance the homogeneous distribution of Mn on the
γ-Al2O3, which may beneft for increasing the BET surface
of the catalyst [37]. This was also confrmed by the XRD.
Fig. 1 The X-ray difraction patterns of the catalysts
Table 1 The BET surface area,
pore volume and pore size of
catalysts
Catalysts
Surface area
(m2 g−1 a
Pore volume (cm3 g−1 b
)
Pore diameter (nm)
)
γ-Al2O3
136
130
129
120
98
9
6
7
8
6
3
7
9
0.194 0.016
0.224 0.011
0.225 0.015
0.225 0.011
0.188 0.010
0.161 0.009
0.207 0.011
0.176 0.010
56.75 1.23
68.60 1.03
69.60 0.93
69.60 0.89
76.78 1.03
73.20 1.10
67.95 0.96
66.16 0.93
3Mn/γ-Al2O3
5Mn/γ-Al2O3
10Mn/γ-Al2O3
15Mn/γ-Al2O3
20Mn/γ-Al2O3
10Fe/γ-Al2O3
10Fe–15Mn/γ-Al2O3
88
122
106
aSurface area was calculated using the BET method at P/P0=0.05–0.3
bTotal pore volume at P/P0 =0.995
1 3

L. Qin et al.
surface of γ-Al2O3 were amorphous [17]. The introduction
of Fe resulted in a higher distribution of Mn over the surface
of the 10Fe–15Mn/γ-Al2O3 catalyst. Therefore, interaction
between Fe and Mn contributed to the homogeneous dis-
tribution of Fe and Mn and suppressed the crystallization
of Fe and Mn. The better distribution and amorphous of Fe
and Mn in the catalysts exhibited a higher toluene oxidation
activity, which was also confrmed by the toluene oxidation
activities.
peak at 380 °C) was mainly assigned to the reduction of
Fe2O3 to Fe3O4. The third stage with temperature range of
400–500 °C belongded to the reduction of Mn2O3 to Mn3O4.
The last stage (500–850 °C) was likely originated from the
reduction of Fe3O4 to FeO, FeO to Fe° and Mn3O4 to MnO.
According to the calculation, the theoretical H2 con-
sumption were in sequence as 331, 354 and 604 μmol g−1
for the 15Mn/γ-Al2O3, 10Fe/γ-Al2O3 and 10Fe–15Mn/γ-
Al2O3. However, the H2 consumption results of H2-TPR
exhibited that the reduction of the 10Fe–15Mn/γ-Al2O3
(513 μmol g−1) consumed much more H2 than that of
the 15Mn/γ-Al2O3 (254 μmol g−1) and the 10Fe/γ-Al2O3
(278 μmol g−1), indicated that more oxygen species in the
10Fe–15Mn/γ-Al2O3, as shown in Table 2. The above value
inferred that the reduction extent of 15Mn/γ-Al2O3, 10Fe/γ-
Al2O3 and 10Fe–15Mn/γ-Al2O3 were 76.74%, 78.53%, and
84.93%, respectively. It also can be seen from the H2-TPR
curves that the reduction peaks were shifted to a lower tem-
perature, indicating that the 10Fe–15Mn/γ-Al2O3 was more
easily reduced by H2 with respect to the 10Fe/γ-Al2O3 and
15Mn/γ-Al2O3. The above phenomena can be explained that
more active component migrates from the bulk to the surface
of the 10Fe–15Mn/γ-Al2O3 catalyst [37], which is also con-
frmed by the ICP/MS results that the Mn concentration on
the surface of catalyst increases from 1.82 to 2.01% after the
introduction of 10% Fe2O3 into the 15Mn/γ-Al2O3 catalyst,
as shown in Table 2.
3.1.3 H2‑TPR
In this study, H2-TPR experiment was carried out to study
the redox performance of these Fe–Mn/γ-Al2O3 catalysts, as
presented in Fig. 2. Previous studies reported that the reduc-
tion of Fe2O3 to Fe3O4 happened at 400 °C, the reduction
Fe3O4 to FeO took place at 660 °C, and FeO was reduced
to form Fe° occurred at 760 °C [38]. As for the MnO2, the
reduction of MnO2 to Mn2O3 took place at 339 °C, Mn2O3
to Mn3O4 at 472 °C and Mn3O4 to MnO at 607 °C [40]. With
respect to the 10Fe/γ-Al2O3, there were two broad peaks
range of 300–450 °C and 500–650 °C (located at 350 °C
and 530 °C) observed. The reduction peak at 350 °C was
assigned to the reduction of Fe2O3 to Fe3O4, and the other
peak at 530 °C represented the reduction of Fe3O4 to FeO
since the FeO was stabilized on Al2O3 support and the strong
interaction between Fe and Al2O3 inhibited the transforma-
tion of FeO to Fe. For the 15Mn/γ-Al2O3, there were only
two peaks found. The frst peak (happened at 300–400 °C,
peak at 375 °C) was attributed to the reduction of MnO2 to
Mn2O3; the other peak (occurred at 400–460 °C, peak at
446 °C) was corresponding to the reduction of Mn2O3 to
Mn3O4. With respect to the 10Fe–15Mn/γ-Al2O3, there were
four peaks observed. The frst stage (occurs at 200–340 °C,
peak at 310 °C) was attributed to the reduction of MnO2
to Mn2O3. The second stage (happened at 340–400 °C,
3.1.4 XPS
XPS was employed to analyze the elemental composition of
these Fe–Mn/γ-Al2O3 catalysts, as displayed in Fig. 3 and
Table 2. In the survey spectrum, four main peaks attribut-
ing to the binding energies of Al (2p), O(1s), Fe(2p) and
Mn(2p) were observed in the 10Fe–15Mn/γ-Al2O3, as noted
in Fig. 3a. Figure 3b indicated that two main bands corre-
sponding to the Mn 2p3/2 and Mn 2p1/2 were found from
638 to 658 eV in the Mn 2p XPS spectra. Meanwhile, the
Mn 2p3/2 spectra of these catalysts by a peak-ftting treat-
ment were divided into two peaks, which were attributed to
Mn4+ and Mn3+ in these catalyst. The binding energies of
Mn4+ and Mn3+ located at the Mn 2p3/2 spectra of these
catalysts were observed at about 643.5 and 641.4 eV, respec-
tively. The ratio of Mn3+/(Mn3+ + Mn4+) was calculated
according to the integral area of the Mn 2p peaks, as shown
in Table 2. The Mn3+/(Mn3++Mn4+) ratios for the 15Mn/γ-
Al2O3 and 10Fe–15Mn/γ-Al2O3 catalysts are 0.47 and 0.53,
respectively. Therefore, the incorporation of Fe into 15Mn/γ-
Al2O3 increases the Mn3+/(Mn3++Mn4+) ratio and provide
a relatively stability on the Fe3+ and Mn3+/(Mn3++Mn4+)
sites [36].
30
310
10Fe/Al O
2
3
25
20
15
10
5
15Mn/Al O
2
3
10Fe-15Mn/Al O
2
3
380
375
446
530
580
0
350
100
200
300
400
500
600
700
800
900
Temperature (°C)
Figure 3c exhibited the Fe 2p spectra of the 10Fe/γ-Al2O3
and 10Fe–15Mn/γ-Al2O3 catalysts. The Fe species located
Fig. 2 H2-TPR profles of the catalysts
1 3

Iron Oxide as a Promoter for Toluene Catalytic Oxidation Over Fe–Mn/γ-Al2O3 Catalysts
between 704.0 and 736.0 eV were ascribed to the Fe 2p3/2
and Fe 2p1/2 species. The peaks of Fe 2p3/2 and Fe 2p1/2
for the 10Fe/γ-Al2O3 were located at 710.7 and 723.9 eV,
respectively, while the peaks of Fe 2p3/2 and Fe 2p1/2 for
the 10Fe/γ-Al2O3 were located at 711.4 and 722.8 eV. The
above results indicated that the Fe3+ was abundant in these
two catalysts. Table 2 also showed that the Fe concentration
in the 10Fe/γ-Al2O3 was 1.32%, while the Fe concentration
was decreased to 0.89% in the 10Fe–15Mn/γ-Al2O3. Com-
pared with the 10Fe/γ-Al2O3, the Fe3+/(Fe2++Fe3+) ratio
was increased from 33.90 to 46.98% for the 10Fe–15Mn/γ-
Al2O3. The above results also proved that the interaction
efect existed between Fe and Mn during impregnation pro-
cess, and the incorporation of the Fe caused the Mn to accu-
mulate on the surface of catalysts, which favored to promote
the catalytic oxidation reaction. In addition, the abundant
of Fe3+ and Mn3+ over the 10Fe–15Mn/γ-Al2O3 catalyst
favored for the oxygen transfer in the catalyst.
Figure 3d presented the O 1s spectra of these catalysts.
The O 1s spectra of these catalysts can be ftted with two
peaks, except for the 10Fe–15Mn/γ-Al2O3. The binding
energy at 529.6–529.7 eV was assigned to the surface lattice
oxygen (Oα), while the binding energy at 531.0–531.1 eV
was attributed to the surface adsorbed oxygen (Oβ). Com-
pared with the 15Mn/γ-Al2O3, the binding energies of Oα
and Oβ in the 10Fe–15Mn/γ-Al2O3 were shifted to the low
values (Oα 0.5 eV, Oβ 1.0 eV), indicating that the O spe-
cies in the 10Fe–15Mn/γ-Al2O3 was more active that was
more benefcial to the toluene oxidation [37]. Meanwhile,
only the 10Fe–15Mn/γ-Al2O3 exhibited a peak at 531.8 eV
that may be corresponding to the adsorbed molecular water
species (Oγ), which may result in higher water resistance
for the 10Fe–15Mn/γ-Al2O3. The (Oβ +Oγ)/(Oα +Oβ +Oγ)
ratio for the 15Mn/γ-Al2O3 was 41.52%, while the (Oβ +Oγ)/
(Oα + Oβ + Oγ) ratio for the 10Fe–15Mn/γ-Al2O3 was
76.72%. The above results indicated that the 10Fe–15Mn/γ-
Al2O3 contained higher contents of Oβ and Oγ. The higher
content of the Oβ was normally thought to be important for
catalytic activity, while the higher content of Oγ was beneft-
able for water resistance [17]. This was also proved by the
experimental results, as presented in Figs. 5 and 6.
3.2 Catalytic Oxidation Activity
The efects of Mn-loading γ-Al2O3 or Fe-loading γ-Al2O3 on
the toluene conversion under diferent reaction temperatures
were presented in Fig. 4. As noted in Fig. 4a, the toluene
conversions over the Mn/γ-Al2O3 catalysts were all increased
as the reaction temperature increased from 100 to 400 °C.
After 5–20% of MnO2 doping into the pure γ-Al2O3, the
toluene conversions under various temperatures were higher
than that of the pure MnO2. Figure 4a also represented that
the toluene conversion increased as the MnO2 loading
1 3

L. Qin et al.
Fig. 3 XPS profles of catalysts:
a survey; b Mn-2p3/2 orbital; c
Fe-2p3/2 orbital; d O-1 s orbital
(d)
O 1s
(a)
Mn 2p
Mn3+
641.2eV
Al 2p
652.8eV
Mn 2p
Mn 3s
Mn4+
C 1s
643.6eV
5Mn/Al2O3
5Mn
/
Al2O3
641.4eV
641.5eV
653.2eV
10Mn/Al2O3
643.5eV
643.5eV
643.6eV
10Mn
/Al2O3
15Mn/Al2O3
20Mn/Al2O3
653.2eV
15Mn
/
Al2O3
641.4eV
653.2eV
Fe 2p
10Fe/Al2O3
20Mn
/
Al2O3
641.8eV
653.2eV
644eV
10Fe-15Mn/Al2O3
1000 800
10Fe-15Mn
/
Al2O3
652
600
400
200
0
656
648
644
640
Binding Energy(eV)
Binding Energy (eV)
(b) Fe 2p
(c) O 1s
710.7eV
Fe3+
531.2eV
723.9eV
529.4eV
O
β
O
α
727eV
713.6eV
5Mn/Al2O3
10Mn/Al2O3
15Mn/Al2O3
529.3eV
531.4eV
O
O
α
β
10Fe/Al2O3
529.6eV
531.2eV
529.6eV
529.6eV
711.4eV
531.2eV
531.2eV
726.1eV
722.8eV
20Mn/Al2O3
10Fe-15Mn/Al2O3
10Fe/Al2O3
530.1eV
531.8eV
529.2eV
α
O
β
O
Oλ
10Fe-15Mn/Al2O3
736 732 728 724 720 716 712 708 704
535 534 533 532 531 530 529 528 527
Binding Energy(eV)
Binding Energy (eV)
was increased from 0 to 15%, while the toluene oxidation
activity were not increased as the MnO2 loading was fur-
ther increased from 15 to 20%. Meanwhile, more than 80%
of the toluene conversion over the 15Mn/γ-Al2O3 catalyst
could be obtained at 200–400 °C, and the toluene conver-
sion was as high as 92.11% at 300 °C, further increase of
temperature can’t obviously enhance the toluene conversion.
Therefore, the optimal temperature was 300 °C and the best
MnO2-loading is 15%. The efect of Fe2O3-loading γ-Al2O3
on the toluene conversion at diferent reaction temperatures
were represented in Fig. 4b. Similar with the Mn/γ-Al2O3
catalyst, the toluene conversions under various tempera-
tures were increased as the Fe2O3-loading was increased
from 3 to 15%, further increase of Fe2O3-loading also can’t
increase the activity, and the maximum toluene conversion
of 46.25% over the 15Fe/γ-Al2O3 catalyst was obtained at
400 °C. Moreover, the efects of GHSV, O2 content and H2O
content on the toluene oxidation performance were investi-
gated over the 15Mn/γ-Al2O3 and 15Fe/γ-Al2O3 catalysts,
as shown in Fig. S1–Fig. S3. The results indicated that the
toluene conversion decreased as the GHSV was increased
from 10,000 to 30,000 h−1 under various temperature. Mean-
while, the toluene conversion increased as the O2 content
was increased from 3 to 10%, while further increased of
the O2 content can’t increase the toluene conversion. Fig.
S3 indicated the toluene conversion over the 15Mn/γ-Al2O3
catalyst gradually decreased from 92.31 to 84.58% for 6 h,
and the CO2 yield reduced from 92 to 76% when the 10
vol% of water was introduced, indicating that the 15Mn/γ-
Al2O3 displayed a higher catalytic activity, and it should be
modifed to enhance the moisture toleration. The toluene
oxidation consumed oxygen and released H2O and CO2, and
1 3

Iron Oxide as a Promoter for Toluene Catalytic Oxidation Over Fe–Mn/γ-Al2O3 Catalysts
100
100
80
60
40
20
0
(a)
(a)
80
60
40
20
0
MnO
2
λ
-Al O
2 3
15Mn/l-Al2O3
3Mn/Al O
2
5Mn/Al O
3
3
3Fe-15Mn/l-Al2O3
5Fe-15Mn/l-Al2O3
10Fe-15Mn/l-Al2O3
15Fe-15Mn/l-Al2O3
20Fe-15Mn/l-Al2O3
2
10Mn/Al O
2
3
3
3
15Mn/Al O
2
20Mn/Al O
2
Duran[28]
Ma[35]
100
150
200
250
300
350
400
100
150
200
250
300
350
400
Temperature (°C)
Temperature (°C)
30
25
20
15
10
5
Fe O
2
3
(b)
(b)
λ
-Al O
2 3
Benzoic acid
Benzaldehyde
50
40
30
20
10
0
3Fe/Al O
2
5Fe/Al O
2
10Fe/Al O
2
3
3
3
3
3
15Fe/Al O
2
20Fe/Al O
2
0
0
5
10
15
20
100
150
200
250
300
350
400
Fe-doping into Mn/ –Al O (%)
λ
2
3
Temperature (°C)
Fig. 5 Efect of Fe-doping into 15Mn/γ-Al2O3 catalyst on the toluene
Fig. 4 The efects of Mn-loading γ-Al2O3 or Fe-loading γ-Al2O3 on
conversion and byproducts formation
toluene conversion
100
the reaction followed toluene → benzaldehyde → benzoic
acid→H2O+CO2 steps [22]. According to the reaction, the
presence of the H2O was unfavorable for the reactions [17].
Therefore, the introduction of H2O had negative infuence
on the CO2 yield as well as the toluene oxidation efciency.
However, the toluene conversion over the 10Fe/γ-Al2O3 sta-
bled at 31.5% and the CO2 yield was 85% in presence of 10
vol% H2O at 300 °C, inferring that the Fe/γ-Al2O3 exhibited
an excellent moisture toleration but lower catalytic activity.
To enhance the VOCs oxidation performance (higher cat-
alytic activity as well as excellent moisture toleration), the
introduction of Fe2O3 into Mn/γ-Al2O3 to prepare Fe–Mn/γ-
Al2O3 catalyst were investigated. Figure 5 displayed the
efect of Fe2O3-doping into 15Mn/γ-Al2O3 catalyst on the
toluene conversion. The results indicated that the toluene
conversion over the xFe–15Mn/γ-Al2O3 at 100–400 °C obvi-
ously increased as the Fe-doping was increased from 0 to
10%, while the toluene conversion varied slightly with the
Fe-doping further increased. It could be seen that 89.15%
and 96.62% of toluene conversion over the 10Fe–15Mn/γ-
Al2O3 were obtained at 200 °C and 300 °C, indicating that
100
95
95
90
85
90
80
85
75
70
H O off
10 vol.% H O on
no water
2
2
80
0
60 120 180 240 300 360 420 480 540 600
Reaction time (min)
Fig. 6 Efect of water vapor on catalytic performance of 10Fe–15Mn/
γ-Al2O3 catalyst
1 3

L. Qin et al.
the toluene oxidation activity over the 10Fe–15Mn/γ-Al2O3
was much better than that obtained from Duran [28] and Ma
[35]. Meanwhile, Fig. 5b also indicated that the byproducts
such as benzaldehyde and benzoic acid were also detected
by the GC/MS at 300 °C, and their contents were decreased
with the Fe-doping. In order to further examine the moisture
toleration of the 10Fe–15Mn/γ-Al2O3 catalyst, the efect of
H2O on the toluene oxidation of the 10Fe–15Mn/γ-Al2O3
was investigated under the GHSV of 20,000 h−1 with 10
vol% H2O at 300 °C, as shown in Fig. 6. The result indicated
95% of the toluene conversion as well as 95% CO2 yield over
the 10Fe–15Mn/γ-Al2O3 sustained for 6 h under the GHSV
of 20,000 h−1 with 10 vol% H2O at 300 °C. Therefore, the
10Fe–15Mn/γ-Al2O3 catalyst showed a good catalytic activ-
ity as well as excellent moisture toleration. There were three
reasons caused the above results: Firstly, the introduction of
Fe into 15Mn/γ-Al2O3 resulted in the formation of Fe–OH
due to the combination of Fe3+ and –OH, which can not
only improves water resistance, but also drives electron
transfer in redox process [37]. Secondly, the change of iron
valence (Fe3+ ⇔ Fe2+ ⇔ Fe) was beneftable for the storing
and releasing oxygen [17]. Lastly, the introduction of Fe into
15Mn/γ-Al2O3 caused Mn to accumulate and homogeneous
distribution on the surface of catalysts, which promoted the
oxidation reaction and enhanced the toluene conversion [41],
as confrmed by XPS and XRD.
2343
(a)
I=0.1
2885
1484
1366
3423
3019
1160
1600
20Mn/Al O
2
3
15Mn/Al O
2
3
10Mn/Al O
2
3
5Mn/Al O
2
3
3
Al O
2
3500
3000
2500
2000
1500
1000
Wavenumber/cm-1
1525
I=0.22
(b)
1704
2343
1488
1366
2885
3423
3019
20Mn/Al2O3
1159
1594
15Mn/Al2O3
10Mn/Al2O3
5Mn/Al2O3
Al2O3
2500
3500
3000
2000
1500
1000
Wavenumber/cm-1
3.3 Mechanism for Catalytic Oxidation of Toluene
The absorption and activation are two main steps for the
toluene oxidation reaction [42]. Therefore, the absorption
and oxidation over the Mn/γ-Al2O3 catalysts were performed
to analyze the transformation of intermediates during the
toluene oxidation process. In this study, toluene absorp-
tion over these catalysts was carried out at 300 °C in Ar
atmosphere, while toluene oxidation was carried out in
presence of O2. The toluene absorption and oxidation over
Mn/γ-Al2O3 catalysts at 300 °C were presented in Fig. 7a
and b. As noted in Fig. 7a, the peak centered at 1600 cm−1
was derived from vibration of aromatic ring, indicating the
toluene was adsorbed over the catalysts and its aromatic
structure keep intact [17]. Two peaks located at 2885 and
3019 cm−1 were observed in the C–H stretching region. One
band at 3019 cm−1 was assigned to the C–H stretching in
aromatic rings, and another band at 2885 cm−1 was attrib-
uted to C–H symmetric or asymmetric stretching of methyl-
ene (–CH2) [22]. The bands appeared at 1160 cm−1 belonged
to the C–O vibration, which was caused by the formation of
alkoxide specie [43]. Meanwhile, the peak corresponding
to alkoxide specie was also detected at 3423 cm−1, which
directly refected the formation of phenyl alcohol [34]. How-
ever, Du et al. [22] claimed that the peak at 1159 cm−1 was
assigned to the C–O vibration from the phenolate. Peaks at
Fig. 7 The profles of toluene desorption and oxidation over Mn/γ-
Al2O3 catalysts: a Ar atmosphere; b O2/Ar atmosphere
1366 cm−1 and 1484 cm−1 belonged to carboxylate, suggest-
ing benzoate species was a key intermediates during tolu-
ene oxidation process [22]. Figure 7a also represented that
the 15Mn/γ-Al2O3 exhibited the highest peaks of adsorbed
toluene (1600 cm−1), alkoxide specie (3423 cm−1) and car-
boxylate (1366 cm−1 and 1484 cm−1) among all the Mn/γ-
Al2O3 catalysts, indicating that the toluene was more easily
adsorbed over the 15Mn/γ-Al2O3, and alkoxide and carboxy-
late species were the main intermediates in the absence of O2
[41]. Peak at 2349 cm−1 was assigned to the CO2, indicating
CO2 can be formed without O2 [44]. Figure 7b presented the
in situ DRIFT spectra of the toluene oxidation over these cat-
alysts in presence of O2. Compared with the spectra obtained
without O2, some obvious changes were found in presence of
O2: (1) The peaks for aldehydic species (peak at 1704 cm−1)
and carboxylate (peak at 1525 cm−1) appeared in presence
of O2 when the Mn-doping was above 5%; (2) The bands for
aldehydic species (peak at 1704 cm−1) and carboxylate (peak
at 1525 cm−1) over the 20Mn/γ-Al2O3 were much higher
than other catalysts, while the peak located at 1594 cm−1
1 3

Iron Oxide as a Promoter for Toluene Catalytic Oxidation Over Fe–Mn/γ-Al2O3 Catalysts
for toluene absorption disappeared over the 20Mn/γ-Al2O3,
suggesting that the adsorbed toluene was easily converted
into other intermediates over the 20Mn/γ-Al2O3 in presence
of O2 with respect to the other Mn/γ-Al2O3; (3) The peaks
belong to CO2 (2343 cm−1), aldehydic species (1704 cm−1)
and C–O vibration (1160 cm−1) in presence of O2 were much
higher than that obtained from Ar atmosphere, indicating
that the intermediates and CO2 from the toluene oxidation
were signifcantly promoted due to the presence of O2. The
above results demonstrated that the gas-phase oxygen had
an greatly infuence on the intermediates formation over the
Mn/γ-Al2O3.
Peak at 1704 cm−1 corresponding to aldehydic species
was observed at 400 °C, indicating the higher tempera-
ture was beneftable for the formation of aldehydic spe-
cies in absence of O2. The carboxylate (located at 1484
and 1366 cm−1) were increased with the temperature.
Meanwhile, the maximum peak of alkoxide specie (at
1160 cm−1) was also obtained at 300 °C. Peak at 2349 m−1
associated with CO2 were increased as the temperature
varied from 200 to 400 °C. The above results implied
that the higher temperature was beneftable for the tolu-
ene absorption over the 15Mn/γ-Al2O3, which was con-
sistent with the results obtained from Fig. 4. The in situ
DRIFT over the 15Mn/γ-Al2O3 for the toluene oxida-
tion at 200–400 °C was represented in Fig. 8b. It was
worthy noted that the peaks belong to CO2 (2349 m−1),
adsorbed toluene (1600 cm−1) and C–O vibration (1160
and 3423 cm−1) in presence of O2 were increased when
the temperature was increased from 200 to 300 °C, while
there was no obvious change as the temperature was fur-
ther increased to 400 °C. Meanwhile, peak at 1704 cm−1
belonged to the C=O were not observed in presence of O2,
indicating the aldehydic species was easily oxidized into
other species (1366 cm−1 and 1484 cm−1) in presence of
O2 at 200–400 °C.
The in situ DRIFT were used to investigate the absorp-
tion and oxidation of toluene over the 15Mn/γ-Al2O3 at
200–400 °C. As noted in Fig. 8a, the peaks correspond-
ing to the adsorbed toluene (1599 cm−1) and C–O vibra-
tion (3424 and 1159 cm−1) are firstly increased and
then decreased at 200–400 °C, and the maximum peak
obtained at 300 °C, indicating adsorbed toluene was con-
verted into other species with the temperature increase.
2349
I=0.17
(a)
3424
1600
1704
2978
1366
In order to evaluate the efect of the Fe-doping into
the 15Mn/γ-Al2O3 on the toluene absorption and oxida-
tion. The in situ DRIFT over the 15Mn/γ-Al2O3, 10Fe/γ-
Al2O3 and 10Fe–15Mn/γ-Al2O3 for the toluene absorp-
tion and oxidation at 300 °C were also compared, as
shown in Fig. 9. Figure 9 indicated that the peaks for CO2
(2343 cm−1), aldehydic (1699 cm−1) and carboxylate (at
1519 cm−1) over the 10Fe–15Mn/γ-Al2O3 were higher
than that obtained from the 15Mn/γ-Al2O3 and 10Fe/γ-
Al2O3, while the adsorbed toluene (1600 cm−1) and C–O
vibration (1160 cm−1) over the 10Fe–15Mn/γ-Al2O3 dis-
appeared with respect to the 15Mn/γ-Al2O3 and 10Fe/γ-
Al2O3, indicating that the 10Fe–15Mn/γ-Al2O3 possessed
the best catalytic activity among these catalysts, which was
more easily oxidized the adsorbed toluene and alkoxide
specie into benzoic acid, CO2 and H2O [45, 46], which
was in accordance with the result of Fig. 5. Compared
with the spectra obtained without oxygen, the peaks for
CO2 (at 2343 cm−1), C=O (at 1704 cm−1) and carboxylate
(at 1525 cm−1) over the 10Fe–15Mn/γ-Al2O3 in presence
of O2 were much higher, implying that the rate of the oxi-
dation reaction was enhanced by the existence of O2. The
above results indicated that the toluene, benzyl alcohol,
and benzoic acid were the main intermediates that could
be directly converted into CO2 in the whole oxidation pro-
cess. Liao et al. [47] also found that the benzyl alcohol,
benzaldehyde and benzoic were the main intermediates
during toluene oxidation process. A similar results were
also obtained by Du et al. [22] and Sun et al. [43].
1484
1159
400 °C
300 °C
200 °C
3500
3000
2500
2000
1500
1000
Wavenumber/cm-1
2342
I=0.22
(b)
3423
1160
3019
1600
1366
400 °C
1484
300 °C
200 °C
3500
3000
2500
2000
1500
1000
Wavenumber/cm-1
Fig. 8 The in situ DRIFT over 15Mn/γ-Al2O3 at 200–400 °C: a Ar
atmosphere; b O2/Ar atmosphere
1 3

L. Qin et al.
(4) The adsorbed toluene over the 10Fe–15Mn/γ-Al2O3
could be oxidized to benzyl alcohol that further oxi-
dized to benzoic acid, and then the benzoic acid was
decomposed into CO2 and H2O.
2343
I=0.22
(a)
1519
1600
1484
1366
1699
3423
1160
Acknowledgements This work was supported by the Technol-
ogy Innovation Special Foundation of Hubei Province (Grant Nos.
2019ACA157, 2019AHB073 and 2019ZYYD060), China Postdoctoral
Science Foundation (2018M642960), and Foundation for Outstanding
Youth Innovative Research Groups of Higher Education Institution in
Hubei Province (T201902).
10Fe-15Mn/Al O
2
3
10Fe/Al O
2
3
15Mn/Al O
2
3
3500
3000
2500
2000
1500
1525
1000
Wavenumber/cm-1
References
2343
I=0.27
(b)
1. Kamal MS, Razzak SA, Hossain MM (2016) Atmos Environ
140:117–134
1594
1704
2. Kansal A (2009) J Hazard Mater 166:17–26
3. Xu M, Yu D, Yao H, Liu X, Qiao Y (2011) Proc Combust Inst
33:1681–1697
4. Chen J, Chen X, Chen X, Xu W, Xu Z, Jia H, Chen J (2018) Appl
Catal B 224:825–835
1160
5. Zhang S, You J, Kennes C, Cheng Z, Ye J, Chen D, Chen J, Wang
L (2018) Chem Eng J 334:2625–2637
10Fe-15Mn/Al O
2
3
10Fe/Al O
2
3
6. Han J, Liang Y, Hu J, Qin L, Street J, Lu Y, Yu F (2017) Energy
Convers Manag 153:641–648
15Mn/Al O
2
3
7. Han J, Zhang L, Kim HJ, Kasadani Y, Li L, Shimizu T (2018) Fuel
Process Technol 176:15–20
8. Zhang Q, Wu L, Fang X, Liu M, Zhang J, Shao M, Lu S, Mao H
(2018) Sci Total Environ 624:878–886
3500
3000
2500
2000
1500
1000
Wavenumber/cm-1
9. Zhang X, Gao B, Creamer AE, Cao C, Li Y (2017) J Hazard Mater
338:102–123
10. Dai C, Zhou Y, Peng H, Huang S, Qin P, Zhang J, Yang Y, Luo L,
Zhang X (2018) J Ind Eng Chem 62:106–119
11. Qin L, Han J, Zhan Y, Chen W, Kim H (2016) Energy Fuels
30:544–550
Fig. 9 The in situ DRIFT spectra over 15Mn/γ-Al2O3, 10Fe/γ-Al2O3
and 10Fe–15Mn/γ-Al2O3 catalysts for the toulene adsorption and oxi-
dation at 300 °C: a Ar atmosphere; b O2/Ar atmosphere
12. Qin L, Han J, Zhao B, Chen W, Xing F (2018) Waste Manag Res
36:1073–1082
4 Conclusions
13. Qin L, Han J, Zhao B, Wang Y, Chen W, Xing F (2018) J Anal
Appl Pyrol 136:132–145
In this study, the Fe-modifed Al2O3-supported Mn mixed
oxide (Fe–Mn/Al2O3) catalysts are prepared using the wet-
impregnation method. These catalysts are characterized by
means of the XRD, BET, XPS, H2-TPR, and in situ DRIFTS.
Meanwhile, the catalytic activities and its mechanism over
Fe–Mn/γ-Al2O3 catalysts for toluene oxidation are also
investigated. The following conclusions have been drawn:
14. Qin L, Xing F, Zhao B, Chen W, Han J (2018) Chemosphere
212:200–208
15. Mustafa MF, Fu X, Liu Y, Abbas Y, Wang H, Lu W (2018) J
Hazard Mater 347:317–324
16. Shayegan Z, Lee C-S, Haghighat F (2018) Chem Eng J
334:2408–2439
17. Chen J, Chen X, Xu W, Xu Z, Chen J, Jia H, Chen J (2017) Chem
Eng J 330:281–293
18. Mirzaei A, Leonardi SG, Neri G (2016) Ceram Int
42:15119–15141
(1) The 10Fe–15Mn/γ-Al2O3 exhibited 95% of toluene con-
version and 95% of CO2 yield as well as good stability
and higher moisture toleration at 300 °C.
19. Du C, Lu S, Wang Q, Buekens AG, Ni M, Debecker DP (2018)
Chem Eng J 334:519–544
20. Castaño MH, Molina R, Moreno S (2017) Mol Catal 443:117–124
21. Ren K, Song J, Song Y-H, Wang H, Liu Z, Liu Z-T, Jiang J, Liu
Z-W (2017) J CO2 Util 22:63–70
(2) The introduction of Fe into Mn/γ-Al2O3 resulted in
higher surface area, higher amount of Mn4+/Mn3+ and
better low-temperature reducibility, as well as homog-
enous distribution of Mn and Fe.
22. Du J, Qu Z, Dong C, Song L, Qin Y, Huang N (2018) Appl Surf
Sci 433:1025–1035
23. Zhang X, Junhui Y, Jing Y, Ting C, Bei X, Zhe L, Kunfeng Z, Ling
Y, Dannong H (2018) Appl Catal A 566:104–112
24. Wang Y, Yang D, Li S, Zhang L, Zheng G, Guo L (2019) Chem
Eng J 357:258–268
(3) The Fe–Mn/γ-Al2O3 showed a better toluene oxidation
performance with respect to the Fe/γ-Al2O3 and Mn/γ-
Al2O3.
25. Hu J, Li WB, Liu RF (2018) Catal Today 314:147–153
1 3

Iron Oxide as a Promoter for Toluene Catalytic Oxidation Over Fe–Mn/γ-Al2O3 Catalysts
26. Tang A, Hu L, Yang X, Jia Y, Zhang Y (2016) Catal Commun
82:41–45
39. Chen W, Luo J, Qin L, Han J (2015) J Environ Manag
164:146–150
27. Baldi M, Escribano VS, Amores JMG, Milella F, Busca G (1998)
Appl Catal B Environ 17:175–182
40. Cao F, Su S, Xiang J, Wang P, Hu S, Sun L, Zhang A (2015) Fuel
139:232–239
28. Durán FG, Barbero BP, Cadús LE, Rojas C, Centeno MA, Odrio-
zola JA (2009) Appl Catal B 92:194–201
41. Luo Y, Zheng Y, Zuo J, Feng X, Wang X, Zhang T, Zhang K,
Jiang L (2018) J Hazard Mater 349:119–127
42. Farmanzadeh D, Valipour A (2018) Appl Surf Sci 450:509–515
43. Sun H, Liu Z, Chen S, Quan X (2015) Chem Eng J 270:58–65
44. Long Y, Wu S, Xiao Y, Cui P, Zhou H (2018) J Clean Prod
181:784–793
29. Quiroga MMB, Barbero BP, Cadus LE (2014) Appl Catal A
474:26–33
30. Castaño MH, Molina R, Moreno S (2015) Appl Catal A 492:48–59
31. Pozan GS (2012) J Hazard Mater 221–222:124–130
32. Esmaeilirad M, Zabihi M, Shayegan J, Khorasheh F (2017) J Haz-
ard Mater 333:293–307
45. Han J, Liang Y, Qin L, Zhao B, Wang H, Wang Y (2019) Catal
Lett 149:3224–3237
33. Shu Y, Xu Y, Huang H, Ji J, Liang S, Wu M, Leung DYC (2018)
Chemosphere 208:550–558
46. Wang H, Han J, Bo Z, Qin L, Wang Y, Yu F (2019) Mol Catal
475:110486
34. Wang H, Lu Y, Han Y, Lu C, Wan H, Xu Z, Zheng S (2017) Appl
Surf Sci 420:260–266
47. Liao Y, Zhang X, Peng R, Zhao M, Ye D (2017) Appl Surf Sci
405:20–28
35. Ma WJ, Huang Q, Xu Y, Chen YW, Zhu SM, Shen SB (2013)
Ceram Int 39:277–281
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
36. Chen C, Li Y, Ma W, Guo S, Wang Q, Li QX (2017) Sep Purif
Technol 183:1–10
37. Wang X, Wu S, Zou W, Yu S, Gui K, Dong L (2016) Chin J Catal
37:1314–1323
38. Chen W, Li Z, Hu F, Qin L, Han J, Wu G (2018) Appl Surf Sci
439:75–81
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