SBA-15 Templated Mesoporous MnOx for Catalytic Ozonation of Toluene

Article abstract of DOI:10.1007/s10562-019-03000-5

Abstract: γ-MnO₂, β-MnO₂ and Mn₂O₃ with mesoporous structure were prepared as catalysts by using SBA-15 as hard template at different calcination temperatures. The catalysts were characterized by XRD, HRTEM, N₂ adsorption–desorption, XPS, FTIR. The activity of three catalysts for catalytic ozonation of toluene followed the order of β-MnO₂ > γ-MnO₂ > Mn₂O₃. The results showed that the mesoporous β-MnO₂ exhibited the best catalytic performance because it has the highest average oxidation state of Mn and the most abundant surface adsorbed oxygen. Specifically, the toluene conversion could reach to 100% and the CO₂ selectivity could reach up to 83% at 70–90?mg/m³ of toluene concentration over the catalyst. It can be inferred that reaction mechanism consists of two cycles including ozone decomposition and toluene adsorption on active sites of β-MnO₂, which obeys L–H mechanism. The active oxygen (O*) produced in the first cycle can oxidize the toluene molecule adsorbed in the second cycle. Simultaneously, the mesoporous β-MnO₂ had good stability, which reflected that it showed good performance on the catalytic ozonation of toluene during the 47-day test. In summary, this work makes it possible to remove VOCs for reality. Graphic Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-03000-5

Catalysis Letters
https://doi.org/10.1007/s10562-019-03000-5
SBA‑15 Templated Mesoporous MnO for Catalytic Ozonation
x
of Toluene
Yue Yuan1 · Zhiyuan Qin1 · Zhongjun Xu1
Received: 1 August 2019 / Accepted: 15 October 2019
©
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
γ-MnO , β-MnO and Mn O with mesoporous structure were prepared as catalysts by using SBA-15 as hard template at
2
2
2
3
diferent calcination temperatures. The catalysts were characterized by XRD, HRTEM, N adsorption–desorption, XPS,
2
FTIR. The activity oꢀ three catalysts ꢀor catalytic ozonation oꢀ toluene ꢀollowed the order oꢀ β-MnO >γ-MnO >Mn O .
2
2
2
3
The results showed that the mesoporous β-MnO exhibited the best catalytic perꢀormance because it has the highest average
2
oxidation state oꢀ Mn and the most abundant surꢀace adsorbed oxygen. Speciꢁcally, the toluene conversion could reach to
3
1
00% and the CO selectivity could reach up to 83% at 70–90 mg/m oꢀ toluene concentration over the catalyst. It can be
2
inꢀerred that reaction mechanism consists oꢀ two cycles including ozone decomposition and toluene adsorption on active
sites oꢀ β-MnO , which obeys L–H mechanism. The active oxygen (O*) produced in the ꢁrst cycle can oxidize the toluene
2
molecule adsorbed in the second cycle. Simultaneously, the mesoporous β-MnO had good stability, which reꢂected that
2
it showed good perꢀormance on the catalytic ozonation oꢀ toluene during the 47-day test. In summary, this work makes it
possible to remove VOCs ꢀor reality.
*
Zhongjun Xu
xuzj@mail.buct.edu.cn
1
Department oꢀ Environmental Science and Engineering,
Beijing University oꢀ Chemical Technology, Beijing 100029,
China
Vol.:(0
1
123456789)
3

Y. Yuan et al.
Graphic Abstract
Keywords Toluene · Catalytic ozonation · Mesoporous MnO catalysts
x
1
Introduction
that the removal oꢀ toluene should be regarded as a major
challenge in the industrialization process [11].
Volatile organic compounds (VOCs) play an important
role in air pollution, since they may be already toxic at
low concentration, causing severe efects when inhaled
Metal oxides are widely used as catalysts and supports,
they normally exhibit more plentiꢀul and complex surꢀace
compositions and structures than metals [12]. For example,
MnOx and CeO2 display the better catalytic activity ꢀor tolu-
ene [13]. Moreover, it was reported that MnOx showed good
catalytic activity in the oxidation oꢀ the VOCs because oꢀ
the nucleophilic oxygens with great mobility in MnOx [14].
Many materials with diferent microstructure have been
prepared by using mesoporous materials as templates.
Moreover, the textural properties and potential applications
oꢀ the obtained novel materials became highlighted [15].
Mesoporous metal oxides have been ꢀocused on due to their
special skeletal structure and larger surꢀace area as well as
their controllable pore diameter and volume [16, 17]. One
oꢀ the known mesoporous silicanes is the SBA-15 with
[
1–3]. Exposure to VOCs can increase long-term health
risks. Moreover, they can also cause serious environmen-
tal problems as the precursors oꢀ ozone and organic aero-
sols [4]. Conventional methods ꢀor abating VOCs include
condensation, biological degradation, adsorption, and
catalysis oxidation and so on [5–7]. Among them, cata-
lytic ozonation is one oꢀ the oxidation techniques used to
improve the eꢃciency oꢀ ozonation process and it has been
successꢀully applied in the degradation oꢀ VOCs [8–10].
Toluene is well known among VOCs because oꢀ its neuro-
toxicity and widespread existence. Thereꢀore, it is obvious
1
3

SBA-15 Templated Mesoporous MnO for Catalytic Ozonation of Toluene
x
hexagonal arrangements [18, 19]. SBA-15 has been used as
hard template ꢀor the synthesis oꢀ mesoporous metal oxides
because oꢀ its ordered structure and the high thermal stabil-
ity oꢀ silica [20, 21].
model. Fourier transꢀorm inꢀrared (FT-IR) spectra oꢀ samples
were measured using TENSO II (Bruker, Germany) in the
−1
wavelength range oꢀ 450–4000 cm .
In this paper, mesoporous MnO was prepared as catalyst
2.4 Catalyst Activity Measurements
x
by using SBA-15 as hard template at diferent calcination
temperatures, aiming to investigate the toluene conversion
All experiments were conducted in a ꢁxed-bed continuous-
ꢂow reactor at 24–26 °C controlled by air conditioner. 0.62 g
oꢀ catalysts were loaded in a quartz tube with an inner diam-
eter oꢀ 7 mm. Toluene vapor was produced by nitrogen purg-
ing liquid toluene and ozone was ꢀrom ozone generators. The
toluene concentration, ozone concentration and gas ꢂow were
controlled by mass ꢂow meters. H O and CO in the air were
and the CO selectivity during the catalytic ozonation.
2
2
Materials and Methods
2.1 Materials and Reagents
2
2
removed through silica gel and NaOH. Then the airꢂow con-
3
Toluene and sodium hydroxide were both produced in Bei-
jing Chemical Works. Mn(NO ) (50 wt%) aqueous solution
taining a target concentration oꢀ toluene (50~225 mg/m ) and
O (600 ppm) at a ꢂow rate oꢀ 125 mL/min were ꢀed into the
3
2
3
was supplied by Xilong Chemical Materials Co., Ltd.. SBA-
reactor and gas hourly space velocity (GHSV) corresponding
−1
1
5 was obtained ꢀrom Nanjing XFNANO Materials Tech.
to the catalysts was 10,000 h . The concentrations oꢀ toluene
Co., Ltd. All chemicals were oꢀ analytical grade and were
used without ꢀurther puriꢁcation.
and CO at the inlet and outlet oꢀ the reactor were measured by
2
gas chromatography (GC) and the concentrations oꢀ O at the
3
inlet and outlet were monitored by an ozone analyzer. Finally,
2.2 Catalyst Preparation
the toluene conversion and CO selectivity can be calculated
2
by the Eqs. (1) and (2), respectively.
Mn(NO ) (50 wt%) aqueous solution and SBA-15 were
3
2
[
C H ] − [C H ]
7
8 in
7
8 out
used as Mn source and templates, respectively. The molar
C H conversion (%) =
7
(1)
8
[
C H ]
7 8 in
ratio oꢀ SBA-15 (SiO ) to Mn(NO ) is 2:1, SBA-15 was
2
3 2
dipped into Mn(NO ) aqueous solution under stirring con-
3
2
dition ꢀor 4 h and then the mixture was evaporated to dryness
[CO2]out
CO selectivity (%) =
2
ꢀ
ꢁ × 100%
at 80 °C ꢀor 12 h. The dry mixture was calcined at 200 °C ꢀor
7
× [C H ] − [C H ]
7
8 in
7
8 out
4
h. Simultaneously, three other samples were prepared in
(2)
the same ways at calcination temperatures oꢀ 300 °C, 400 °C
and 500 °C, respectively. The SBA-15 templates in the ꢀour
samples were dissolved completely in 2 mol/L NaOH solu-
tion under continuous stirring ꢀor 150 min. The suspensions
were ꢁltered and the ꢁltered products were washed until
their pH approached to 7. Finally, the products were dried
where [C H ] , [C H ] and [CO ] are the inlet concen-
7
8 in
7
8 out
2 out
tration oꢀ C H , the outlet concentration oꢀ C H and the
7
8
7
8
outlet concentration oꢀ CO .
2
3
Results and Discussion
at 60 °C ꢀor 12 h to obtain the mesoporous MnO catalysts.
x
3.1 The Synthesis of Catalysts
2
.3 Catalysts Characterization
The synthesis process oꢀ the catalysts is shown in Fig. 1. When
the mesoporous silica (SBA-15) were immersed by Mn(NO )
3
2
The XRD patterns oꢀ the MnO catalysts were acquired ꢀrom a
2+
x
aqueous solution, Mn entered the channel oꢀ the mesoporous
X-ray powder difractometer (D/Max 2400, Japan) at an elec-
tric current oꢀ 40 mA and a voltage oꢀ 35 kV. The morpholo-
gies and microstructures were acquired ꢀrom a high resolu-
tion-transmission electron microscopy (HRTEM, JEM-3010,
Japan). X-ray photoelectron spectroscopy (XPS) spectra were
obtained by the ESCALAB 250 apparatus ꢀrom ThermoFisher
in USA. The surꢀace areas and pore volumes were acquired
silica and then manganese was oxidized into MnO aꢀter calci-
x
nation [22]. The SBA-15 template was removed by the NaOH
solution and then the synthesis oꢀ the catalysts was completed.
3.2 Characterizations of Catalysts
XRD patterns oꢀ the catalysts are displayed in Fig. 2a. The
results showed that the difraction peaks oꢀ the catalysts cal-
cined at 200 °C and 300 °C corresponded to the (101), (220),
ꢀ
rom the N adsorption–desorption isotherms conducted at
2
7
7 K on ASAP 2460 system ꢀrom USA. The speciꢁc surꢀace
areas were calculated by the Brunayer–Emmett–Teller (BET)
method and mesoporous volume was derived ꢀrom the adsorp-
tion isotherm according to the Barrett–Joyner–Halenda (BJH)
(
102) and (222) planes, agreeing well with γ-MnO (γ-MnO
2 2
ꢀ
ormed at 200 °C and 300 °C are hereinaꢀter reꢀerred to as
1
3

Y. Yuan et al.
The morphologies and microstructures acquired by
HRTEM are given in Fig. 3a, b, which showed that the
lattice ꢀringe with spacing oꢀ 0.243 nm correspond to the
(
220) plane oꢀ γ-MnO (1). Similarly, the exposed ꢀacet
2
oꢀ γ-MnO (2) could be identiꢁed as the (220) plane with
2
the lattice spacing oꢀ 0.243 nm (Fig. 3c, d). Further ꢀrom
Fig. 3e, ꢀ, the lattice ꢀringe spacing were about 0.272 nm and
0
.331 nm corresponding to the (101) and (110) planes oꢀ the
Fig. 1 A schematic diagram oꢀ synthesis oꢀ mesoporous MnOx
β-MnO . Figure 3g, h shows the lattice spacing oꢀ 0.279 nm,
2
corresponding to (222) plane oꢀ the Mn O .
2
3
Figure 4 illustrates the N adsorption–desorption iso-
2
γ-MnO (1) and γ-MnO (2), respectively) crystalline phase
therms and the BJH pore size distribution ꢀor the MnO cata-
2
2
x
(
JCPDS No.17-0510) [23]. However, the difraction peaks
lysts. The N adsorption–desorption isotherms oꢀ the cata-
2
oꢀ the catalysts were broader and lower, which indicated the
lysts were all typical type IV shape with a hysteresis loop
oꢀ type H3, indicating that the catalysts had mesoporous
structure [28, 29]. The BET surꢀace area, pore diameter and
the pore volume are shown in Table 1. The results showed
that β-MnO and γ-MnO (2) had the larger surꢀace area. As
γ-MnO catalysts calcined at 200 °C and 300 °C had a low
2
degree oꢀ crystallization. The difraction peaks in XRD pat-
tern oꢀ the catalyst calcined at 400 °C corresponded to the
(
110), (101), (111), (211), (220), (002), and (112) planes,
2
2
assigned to β-MnO (JCPDS No. 24-0735) [24]. The difrac-
shown in the inset oꢀ Fig. 4, the pore size oꢀ the catalysts was
concentrated at 2–5 nm, which proved that the catalysts had
mesoporous structure.
2
tion peaks in XRD pattern oꢀ the catalyst calcined at 500 °C
matched well with the (211), (222), (400), (420), (431),
(
440) and (622) planes oꢀ Mn O (JCPDF No. 41-1442) [25].
Figure 5 shows Mn 2p, Mn 3s and O 1s XPS spectra oꢀ
the catalysts. XPS results oꢀ surꢀace Mn and O elements oꢀ
the catalysts are displayed in Table 2. The obtained binding
energy values oꢀ Mn 2p and Mn 2p ꢀor all MnO were
2
3
The results indicated that the crystallization degree oꢀ cata-
lyst became better with the increase oꢀ calcination tempera-
ture. However, MnO transꢀormed completely into Mn O
2
2
3
3/2
1/2
x
when increasing the calcinations temperature to 500 °C. Fig-
ure 2b shows that the low and wide angle XRD patterns oꢀ
SBA-15, which showed that SBA-15 had a broad difraction
peak oꢀ mesoporous silica at 22° (2θ) [26]. Moreover, three
difraction peaks were assigned to (100), (110) and (200)
planes, indicating SBA-15 has highly ordered hexagonal
tunnel structure [27].
at range oꢀ 641.3–641.6 eV and 652.9–653.4 eV, respec-
tively. The binding energy separation between Mn 2p and
3
/2
Mn 2p ꢀor γ-MnO and β-MnO were 11.7 and 11.8 eV,
1
/2
2
2
respectively, while the separation was 11.6 eV ꢀor Mn O
2
3
4
+
(Table 2), which conꢁrmed that Mn was major in as-syn-
3
+
thesized γ-MnO and β-MnO while Mn was dominant in
2
2
as-synthesized Mn O [30–33].
2
3
Fig. 2 XRD patterns oꢀ MnO and SBA-15. a γ-MnO (1) calcined at 200 °C, γ-MnO (2) calcined at 300 °C, β-MnO calcined at 400 °C, Mn O
3
x
2
2
2
2
calcined at 500 °C, b low and wide angle XRD patterns oꢀ SBA-15
1
3

SBA-15 Templated Mesoporous MnO for Catalytic Ozonation of Toluene
x
Fig. 3 HRTEM images oꢀ the
MnO catalysts. a, b γ-MnO (1)
x
2
calcined at 200 °C, c, d
γ-MnO (2) calcined at 300 °C,
2
e, f β-MnO calcined at 400 °C,
2
g , h Mn O calcined at 500 °C
2
3
The average oxidation state (AOS) oꢀ Mn were calculated
the sequence: β-MnO >γ-MnO (2)>γ-MnO (1)>Mn O .
2 2 2 2 3
using the ꢀormula [34]: AOS = 8.956–1.126 ΔE , where
This result suggested that β-MnO has the most abundant
S
2
ΔE is the binding energy oꢀ the doublet separation oꢀ Mn
surꢀace adsorbed oxygen, which is an active oxide group ꢀor
S
3
s peaks as shown in Fig. 5. Table 2 shows the AOS val-
catalytic ozonation [38].
ues oꢀ Mn were 3.28–3.78, which were consistent with the
result reported by Peluso et al. [35]. The results showed that
3.3 Catalyst Activity
the AOS values decreases in the order oꢀ β-MnO > γ-M
2
nO (2)>γ-MnO (1)>Mn O , which showed that the con-
The catalytic perꢀormance including toluene conversion and
2
2
2
3
4
+
tent oꢀ Mn in the β-MnO is the highest. The O1s peaks
CO selectivity oꢀ catalysts were tested ꢀor 7 days and the
2
2
could be ꢁtted into two peaks reꢀerred to the chemisorbed
data are shown in Fig. 6a, b. The results demonstrated that
oxygen (O , 531.0–531.1 eV) and the lattice oxygen (O ,
the valence and crystal oꢀ MnO have a great inꢂuence on the
α
β
x
5
28.8–529.3 eV) [36]. Chemisorbed oxygen contains ꢀree
activity oꢀ the catalysts. Among MnO , β-MnO presented
x
2
oxygen radical and hydroxyl oxygen [37]. Table 2 shows
that the surꢀace element molar ratios oꢀ O /O decreased in
the best perꢀormance as the toluene conversion and the CO
2
selectivity could reach to 100% and 73%, respectively. The
α
β
1
3

Y. Yuan et al.
3
even iꢀ the toluene concentration increased to 225 mg/m .
3
When a lower concentration (50–150 mg/m ) oꢀ toluene was
ꢀ
ed, the CO selectivity could be reach up to 83%. CO selec-
2 2
tivity decreases signiꢁcantly as the concentration oꢀ toluene
3
was greater than 150 mg/m , and the CO selectivity was
2
stable at about 73% during the concentration oꢀ toluene was
3
1
50–160 mg/m .
As can be seen ꢀrom Fig. 7, high concentrations oꢀ tolu-
ene did not cause toxic efects on the catalyst or made it
inactive during this process, which indicated a small part
oꢀ intermediate products ꢀrom toluene decomposition were
adsorbed on the catalyst surꢀace. When the inlet concentra-
tion oꢀ toluene increased, more toluene molecules would
compete with the intermediate products ꢀor active sites. As
a result, more intermediate products could not be oxidized
completely, ꢀurther resulting in the decrease oꢀ CO selec-
2
tivity. Feng et al. ꢀound that hollow spheres CeO showed
2
Fig. 4 Nitrogen adsorption–desorption isotherms and the corre-
the good catalytic activity ꢀor toluene degradation with 90%
sponding pore size distribution oꢀ the MnO . γ-MnO (1) calcined at
x
2
toluene conversion at 207 °C [41]. However, in our work,
2
00 °C, γ-MnO (2) calcined at 300 °C, β-MnO calcined at 400 °C,
2
2
mesoporous β-MnO exhibited the best catalytic perꢀor-
2
Mn O calcined at 500 °C
2
3
mance with 100% toluene conversion at room temperature
(
Fig. 7). The results showed that catalytic ozonation is a
Table 1 BET surꢀace area, pore diameter and pore volume oꢀ cata-
more efective and energy-saving method than catalytic com-
lysts
bustion ꢀor removing toluene. MnO is one oꢀ the most stud-
2
ied high-eꢃciency ozone catalysts. Simultaneously, SBA-15
with hollow nanostructures are ꢀavorable ꢀor the ꢁlling oꢀ
precursors to ꢀorm ordered structures so that it is an ideal
template ꢀor the preparation oꢀ mesoporous catalysts. SBA-
Catalysts
Speciꢁc surꢀace
Pore diameter Pore
2
area (m /g)
(nm)
volume
3
(
cm /g)
γ-MnO (1)
61
103
106
60
2.1
2.3
3.4
2.4
0.38
0.39
0.28
0.40
2
15 templated β-MnO had ordered mesoporous structure and
γ-MnO (2)
2
2
high chemisorbed oxygen concentration, which are ꢀavora-
ble to enhance the perꢀormance oꢀ the catalyst. Ryu et al.
β-MnO2
Mn O3
2
ꢀ
ound that Mn/γ-Al O displays excellent catalytic activity
2 3
ꢀ
or toluene removal at room temperature but it deactivated
catalytic perꢀormance oꢀ γ-MnO (2) was similar to β-MnO ,
gradually during the experiment oꢀ 1020 min [42]. How-
2
2
but it showed lower CO selectivity (67%–70%). Both the
ever, Fig. 7 illustrated the stability oꢀ mesoporous β-MnO
2
2
toluene conversion and CO selectivity oꢀ γ-MnO (1) and
with the best catalytic perꢀormance was also checked by a
long-term at room temperature and catalyst still exhibited
100% toluene conversion during 47-day test. Mesoporous
2
2
Mn O have decreased with time, indicating that γ-MnO (1)
2
3
2
and Mn O exhibited much lower catalytic activity. As a
2
3
result, the ꢀour catalysts showed the diferent activities on
the catalytic ozonation oꢀ toluene ꢀollowing the sequence
oꢀ β-MnO >γ-MnO (2)>γ-MnO (1)>Mn O . Chen et al.
β-MnO has better catalytic perꢀormance and stability com-
2
pared with Mn/γ-Al O . Generally, byproducts depositing on
2
3
the catalysts will cause catalyst deactivation. In our study,
2
2
2
2
3
pointed that O has higher mobility than O and the ꢀormer
mesoporous β-MnO still had good catalytic activity during
α
β
2
can actively participate in the oxidation process and greatly
promote catalytic activity [39]. As revealed by XPS analy-
sis, β-MnO contained the highest content oꢀ O so that it
the 47-day test, which indicated that there may not be lots oꢀ
by-products depositing on the catalyst surꢀace to deactivate
the catalyst.
2
α
showed good catalytic activity. In addition, β-MnO has the
2
largest AOS value that afects the activity oꢀ the catalyst.
The higher the AOS, the stronger the activity oꢀ the catalysts
in the catalytic oxidation reaction [40].
3.4 Mechanism Analysis
As it shows in Fig. 8, the composition oꢀ the ꢀresh MnO and
2
The durability oꢀ catalysts is very important in applica-
reacted MnO were determined by FTIR analysis. Table 3
2
tion. A 47-day perꢀormance oꢀ mesoporous β-MnO was
presents a summary oꢀ the ꢀunctional groups observed in
2
−
1
investigated ꢀor the catalytic ozonation oꢀ toluene. Figure 7
the FTIR spectra. The peaks oꢀ catalyst at about 566 cm
−
1
shows that toluene conversion could still reach nearly 100%
and 505 cm were attributed to the stretching vibration
1
3

SBA-15 Templated Mesoporous MnO for Catalytic Ozonation of Toluene
x
Fig. 5 Mn 2p, Mn 3s and O 1s XPS spectra oꢀ the catalysts. a γ-MnO (1), b γ-MnO (2), c β-MnO , d Mn O
2
2
2
2
3
Table 2 XPS results oꢀ surꢀace
Mn and O elements oꢀ the ꢀour
catalysts
Catalysts
Mn2p
Mn3s
O1s
Mn2p1/2 (eV)
Mn2p3/2 (eV)
ΔE (eV)
AOS oꢀ Mn
O (%)
O (%)
O /Oβ
S
α
β
α
γ-MnO (1)
653.4
653.3
653.1
652.9
641.6
641.6
641.4
641.3
11.8
11.7
11.7
11.6
3.60
3.65
3.79
3.28
39
41
44
32
61
59
56
68
0.64
0.69
0.78
0.47
2
γ-MnO (2)
2
β-MnO2
Mn O
2
3
oꢀ Mn–O bonds, which indicated the MnO had already
decomposition oꢀ ozone is the key ꢀor the catalytic ozonation
oꢀ toluene. It is speculated that ozone is decomposed into
2
ꢀ
ormed. According to the FTIR spectra ꢀrom reacted MnO ,
2
it is speculated that the intermediate products ꢀrom toluene
O and O* ꢁrstly at the active sites. The bond energies oꢀ
2
decomposition may contain acids, alcohols, chain hydro-
carbons and so on. During the process oꢀ the catalytic
ozonation oꢀ toluene, the active oxygen (O*) by catalytic
C H CH –H and C H –CH in toluene are 317 and 414 eV,
6
5
2
6
5
3
respectively, indicating that the bond oꢀ C H CH –H is more
6
5
2
easily oxidized so that we consider toluene is oxidized to
1
3

Y. Yuan et al.
Fig. 6 Toluene conversion (a) and CO selectivity (b) under the cat-
200 °C, γ-MnO (2) calcined at 300 °C, β-MnO calcined at 400 °C,
2
2
2
3
alytic ozonation over the catalysts at 600 ppm O , 140 mg/m tolu-
Mn O calcined at 500 °C
3
2
3
−
1
ene, 10,000 h GHSV and room temperature. γ-MnO (1) calcined at
2
Fig. 7 The perꢀormance oꢀ mesoporous β-MnO on the catalytic ozo-
2
−1
nation oꢀ toluene during 47 days at 600 ppm O , 10,000 h GHSV
3
and room temperature
Fig. 8 FTIR spectra oꢀ ꢀresh and reacted mesoporous β-MnO2
benzyl alcohol (3374 cm−1 and 1100 cm ) at the beginning
oꢀ the reaction [43]. The OH on benzyl alcohol is broken
to ꢀorm ꢀree ·OH, which cooperate with the O* to oxidize
the benzyl alcohol to benzoic aldehyde and benzoic acid
−1
[45]. It can be inꢀerred that the reaction mechanism consists
oꢀ two cycles including ozone decomposition and toluene
−1
(
1390 cm ) [44]. Then they are ꢀurther deeply oxidized into
small molecules such as acetaldehyde, ethanol and acetone
Fig. 9) and these small molecules are oxidized to harm-
adsorption on active sites oꢀ β-MnO . O* produced in the
2
ꢁrst cycle can oxidize the toluene molecule adsorbed in the
(
second cycle, the toluene ꢁnally was oxide to H O and CO .
2
2
less H O and CO ꢁnally. The catalytic ozonation process
In addition, Aghbolaghy et al. ꢀound that byproducts such
as acetic acid and ꢀormic acid accumulated on the catalyst
surꢀace could decrease the catalyst activity [46]. However,
as shown in Fig. 8, there are not many organic acids attached
to the catalyst surꢀace to afect the activity and stability oꢀ
the catalyst.
2
2
oꢀ toluene is shown in Fig. 10. Thereꢀore, the main reactive
oxygen species include O* ꢀormed ꢀrom the O decomposi-
3
tion and ·OH. In addition, the catalytic ozonation oꢀ toluene
over MnO /graphene was a heterogeneous reaction and the
2
Langmuir–Hinshelwood (L–H) mechanism was applicable
1
3

SBA-15 Templated Mesoporous MnO for Catalytic Ozonation of Toluene
x
Table 3 Assignment oꢀ FTIR
Signiꢁcant band (cm−1
)
Assigned ꢀunctional groups
Mn–O stretching vibration
bands appearing at the samples
1
−1
5
1
66 cm− , 505 cm
390 cm−
1
Methyl C–H bending, antisymmetric and symmetric
COO– stretching oꢀ carboxylates
1
1
3
1
623 cm−
640 cm
1
C=C stretching vibration
C=O stretching vibration
OH stretching oꢀ alcohols, carboxylic acids and water
C–O stretching vibration
−1
397 cm− , 3374 cm−1, 1634 cm−1
100 cm−
1
1
Fig. 9 GC-MS diagram oꢀ
organic byproducts in the outlet
gas ꢀrom the catalytic ozonation
oꢀ toluene over mesoporous
β-MnO2
Fig. 10 The process oꢀ catalytic
ozonation oꢀ toluene over
mesoporous β-MnO2
4
Conclusion
mainly attributed to O* generated ꢀrom ozone decompo-
sition over the active sites oꢀ catalysts. In addition, the
mesoporous β-MnO2 has good stability, which reꢂected
that it showed good perꢀormance on the catalytic ozona-
tion oꢀ toluene during the 47-day test at room tempera-
ture. Mesoporous β-MnO2 has an excellent activity and
stability ꢀor catalytic ozonation oꢀ toluene since there are
no enough organic acids attached to the catalyst surꢀace.
Moreover, the two cycles including ozone decomposition
and adsorbed toluene on the active sites obeys the L–H
mechanism is proposed.
In this paper, mesoporous MnO catalysts were prepared
x
by using SBA-15 as hard template and tested ꢀor cata-
lytic ozonation oꢀ toluene. Mesoporous β-MnO showed
2
the best catalytic activity among them. Mesoporous
β-MnO has the highest average oxidation state (AOS) oꢀ
2
Mn and the most abundant surꢀace adsorbed oxygen. In
the process oꢀ catalytic ozonation oꢀ toluene, the toluene
conversion and CO selectivity could reach up to 100%
2
and 83%, respectively. The high catalytic activity oꢀ the
mesoporous β-MnO ꢀor catalytic ozonation oꢀ toluene is
2
Acknowledgements The authors thank Shanshan Li ꢀor her perꢀect
support during the experiment.
1
3

Y. Yuan et al.
2
2
2
2
4. Ye Q, Zhao J, Huo F, Wang D, Cheng S, Kang T, Dai H (2013)
Microporous Mesoporous Mater 172:20–29
Compliance with Ethical Standards
5. Parveen N, Khan Z, Ansari SA, Park S, Senthilkumar ST, Kim Y,
Ko H, Cho MH (2019) Chem Eng J 360:415–422
Conflict of interest The authors declare that they have no conꢂict oꢀ
interest.
6. Pattnayak A, Madhu N, Panda AS, Sahoo MK, Mohanta K (2018)
Mater Today 5:8184–8192
7. Lakhi KS, Singh G, Kim S, Baskar AV, Joseph S, Yang J-H,
Ilbeygi H, Ruban SJM, Vu VTH, Vinu A (2018) Microporous
Mesoporous Mater 267:134–141
References
2
8. Bohström Z, Lillerud KP (2018) Microporous Mesoporous Mater
1
2
3
4
5
.
.
.
.
.
Song SK, Shon ZH, Kang YH, Kim KH, Han SB, Kang M, Bang
JH, Oh I (2019) Environ Pollut 247:763–774
Montecchio F, Altimira M, Andersson A, Engvall K (2019) Chem
Eng J 369:280–291
2
71:295–300
2
3
9. Li J, Qu Z, Qin Y, Wang H (2016) Appl Surꢀ Sci 385:234–240
0. Xiao K, Li J-W, Chen G-F, Liu Z-Q, Li N, Su Y-Z (2014) Elec-
trochim Acta 149:341–348
Yang C, Miao G, Pi Y, Xia Q, Wu J, Li Z, Xiao J (2019) Chem
Eng J 370:1128–1153
3
3
3
3
3
3
1. Lee SW, Kim J, Chen S, Hammond PT, Yang SH (2010) ACS
Nano 4:3889–3896
Hu R, Liu G, Zhang H, Xue H, Wang X (2018) Ecotoxicol Environ
Saꢀ 160:301–307
2. Li Q, Anderson JM, Chen Y, Zhai L (2012) Electrochim Acta
5
9:548–557
Son Y-S, Kim T-H, Choi CY, Park J-H, Ahn J-W, Dinh T-V (2018)
Radiat Phys Chem 144:367–372
3. Salavati-Niasari M, Mohandes F, Davar F, Saberyan K (2009)
Appl Surꢀ Sci 256:1476–1480
6
7
.
.
Mok YS, Kim DH (2011) Curr Appl Phys 11:S58–S62
Li J, Na H, Zeng X, Zhu T, Liu Z (2014) Appl Surꢀ Sci
4. Selvakumar S, Nuns N, Trentesaux M, Batra VS, Giraudon JM,
Lamonier JF (2018) Appl Catal B 223:192–200
3
11:690–696
5. Peluso MA, Gambaro LA, Pronsato E, Gazzoli D, Thomas HJ,
Sambeth JE (2008) Catal Today 133–135:487–492
8
9
.
.
Ikhlaq A, Brown DR, Kasprzyk-Hordern B (2015) Appl Catal B
1
65:408–418
6. Tang X, Gao F, Xiang Y, Yi H, Zhao S, Liu X, Li Y (2015) Ind
Eng Chem Res 54:9116–9123
Rezaei F, Moussavi G, Bakhtiari AR, Yamini Y (2016) J Hazard
Mater 306:348–358
3
3
3
7. Jin Q, Shen Y, Zhu S (2017) J Colloid Interꢀace Sci 487:401–409
8. Jia J, Zhang P, Chen L (2016) Appl Catal B 189:210–218
9. Chen H, Sayari A, Adnot A, Larachi F (2001) Appl Catal B
1
1
1
1
1
1
1
0. Rezaei E, Soltan J, Chen N (2013) Appl Catal B 136–137:239–247
1. Zhu J, Li Y, Xu L, Liu Z (2018) Ecotox Environ Saꢀ 165:115–125
2. Huang W (2016) Acc Chem Res 49:520–527
3
2:195–204
3. Qu Z, Gao K, Fu Q, Qin Y (2014) Catal Commun 52:31–35
4. Castaño MH, Molina R, Moreno S (2017) Mol Catal 443:117–124
5. Ren Y, Ma Z, Bruce PG (2012) Chem Soc Rev 41:4909–4927
6. Xaba MS, Noh J-H, Mokgadi K, Meijboom R (2018) Appl Surꢀ
Sci 440:1130–1142
4
4
4
4
4
0. Gao J, Han Y, Mu J, Wu S, Tan F, Shi Y, Li X (2018) J Colloid
Interꢀace Sci 516:254–262
1. Feng Z, Ren Q, Peng R, Mo S, Zhang M, Fu M, Chen L, Ye D
(
2019) Catal Today 332:177–182
2. Ryu HW, Song MY, Park JS, Kim JM, Jung SC, Song J, Kim BJ,
Park YK (2019) Environ Res 172:649–657
1
1
7. Subhan F, Aslam S, Yan Z, Zhen L, Ikram M, Ullah R, Etim UJ,
Ahmad A (2018) Chem Eng J 339:557–565
3. Zhao D, Ding T, Li X, Liu J, Shi C, Zhu A (2012) Chin J Catal
8. Barranco-García R, López-Majada JM, Martínez JC, Gómez-
Elvira JM, Pérez E, Cerrada ML (2018) Microporous Mesoporous
Mater 272:209–216
3
3:396–401
4. Nawaz F, Cao H, Xie Y, Xiao J, Chen Y, Ghazi ZA (2017) Che-
mosphere 168:1457–1466
1
9. Kwon M-H, Chae H-J, Park MB (2018) J Ind Eng Chem
4
4
5. Hu M, Yao Z, Hui KN, Hui KS (2017) Chem Eng J 308:710–718
6. Aghbolaghy M, Soltan J, Sutarto R (2017) Chem Eng Res Des
6
5:397–405
2
2
0. Zhang L, Jaroniec M (2017) J Colloid Interꢀace Sci 501:248–255
1. Singh S, Kumar R, Setiabudi HD, Nanda S (2018) Vo D-VN. J
Colloid Interꢀace Sci 559:57–74
1
28:73–84
Publisher’s Note Springer Nature remains neutral with regard to
2
2
2. Ette PM, Selvakumar K, Senthil Kumar SM, Ramesha K (2018)
Electrochim Acta 292:532–539
jurisdictional claims in published maps and institutional aꢃliations.
3. Xie J, Wei Y, Song X, Chen Y, Zou Q, Wang M, Xu A, Li X
(
2018) J Colloid Interꢀace Sci 529:476–485
1
3