An et al.
Benzene Oxidation with Ozone Over MnOx/MSU-H and MnOx/Mesoporous-SAPO-34 Catalysts
materials with large surface area are advantageous for dis-
persion of Mn. Among other support materials, meso-
porous materials have large specific surface area and large
pores (2 nm–50 nm), enabling large VOC molecules
like benzene to diffuse easily to active metal sites present
in the pores. MCM-41, MCM-48, SBA-15, KIT-6, and
MSU-H are representative mesoporous materials that have
been applied effectively to a number of catalytic reactions.
Mesoporous materials converted from microporous mate-
rials are also widely used.
In this study, benzene, MSU-H, and mesoporous SAPO-
34 (Meso-SAPO-34) were selected as the model VOC,
mesoporous material, and mesoporous material from
microporous material, respectively. MSU-H and Meso-
SAPO-34 have never been applied before for catalytic
oxidation or catalytic ozonation of VOCs. These two
mesoporous materials were impregnated by 15 wt% Mn
and applied to catalytic oxidation with ozone of benzene
to examine their potential for the removal of benzene.
60 ml/min controlled by an MFC. The total flow rate was
120 ml/min, while the concentrations of ozone and ben-
zene were 1000 ppm and 100 ppm, respectively. The size
and mass of the catalyst used for each experiment were
25∼35 mesh and 0.05 g, respectively. Before experiments,
ꢀ
catalysts were calcined for 30 min at 300 C under oxy-
gen condition. Three different reaction temperatures were
used: 50 ꢀC, 80 ꢀC, and 100 ꢀC. Each reaction was allowed
to continue for 150 min. Product gas was analyzed by gas
chromatography equipped with a flame ionization detector
(Young Lin, column HP-5) to determine the concentration
of benzene. An indoor gas analyzer was used to measure
the concentrations of CO and CO2 produced.
3. RESULTS AND DISCUSSION
3.1. Characteristics of Catalysts
Table I compares the specific surface areas and pore vol-
umes of the catalysts. The specific surface area of MSU-H
was 820 m2/g, while it decreased to 370 m2/g after the
impregnation of Mn. The pore volume was also reduced
from 0.98 cm3/g to 0.65 cm3/g by the impregnation of Mn.
This result is attributed to partial blockage of pores by
the impregnated Mn. Similarly, the specific surface area
and pore volume of Meso-SAPO-34 were also reduced
by the impregnation of Mn from 499 m2/g to 225 m2/g
and from 0.58 m3/g to 0.19 m3/g, respectively. The nitro-
2. EXPERIMENTAL DETAILS
2.1. Synthesis of Catalysts
Meso-SAPO-34 was prepared in the presence of carbon
black as a hard template.9 MSU-H was purchased from
Sigma-Aldrich. MSU-H and Meso-SAPO-34 were impreg-
nated by 15 wt% Mn using Mn(CH COO) (Aldrich,
99%+) following the incipient wetness method. The
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gen sorption isotherms shown in Figure 1(a) demonstrate
that both MSU-H and Meso-SAPO-34 exhibit hysteresis,
IP: 81.192.38.119 On: Sun, 13 Mar 2016 01:45:33
15 wt% Mn-impregnated mesoporous catalysts will be
referred to, hereafter, as MnOx/MSU-H and MnOx/Meso-
SAPO-ꢀ34, respectively. These catalystsꢀwere dried for 12 h
at 110 C and calcined for 3 h at 550 C.
Copyright: American Scientific Publishers
a characteristic of mesoporous materials. The slopes of
the isotherms of MSU-H and Meso-SAPO-34 increased
rapidly at P/P0 = 0ꢂ7 and P/P0 = 0ꢂ9, respectively.
When they were impregnated by Mn, MSU-H retained
hysteresis, while the hysteresis of Meso-SAPO-34 was
weakened substantially. As shown in Figure 1(b), the pore
size of MSU-H was ca. 10 nm, while that of Meso-SAPO-
34 was ca 4 nm and 15 nm. After the impregnation of Mn,
similar pore size was observed for MSU-H, whereas most
mesopores of Meso-SAPO-34 disappeared.
Figure 2 compares the XRD patterns of MSU-H and
Meso-SAPO-34 observed before and after the impregna-
tion of Mn. For both MSU-H and Meso-SAPO-34, no Mn
peak was observed after the impregnation of Mn, indicat-
ing MnOx was dispersed well.3ꢃ4 The peak intensity at low
angle shown in Figure 2(a) indicates that the structure of
MSU-H was preserved well. On the other hand, the peak
intensity of Meso-SAPO-34 was dramatically reduced at
2.2. Characterization of Catalysts
The specific surface areas of the catalysts were estimated
using the Brunauer–Emmett–Teller (BET) equation. Pore
size distribution was calculated by the Barrett–Joyner–
Halenda method. The powder X-ray diffraction (XRD)
was determined by X-ray diffractometer (Rigaku D/MAX-
III) using Cu-Kꢁ radiation. N2 adsorption–desorption
isotherms were obtained using a Micromeritics ASAP
2000 at −196 ꢀC (liquid N2ꢀ. H2-Temperature pro-
grammed reduction (TPR) analysis was performed with
0.06 g of calcined catalyst, increasing temperature from
ꢀ
ꢀ
room temperature to 700 C at a rate of 10 C min−1 in
10 wt% H2/He gas flow. The hydrogen consumption was
monitored via a thermal conductivity detector.
Table I. BET surface area, pore volume of the catalysts.
2.3. Benzene Oxidation
BET surface
Pore
A fixed-bed flow reactor was used for the catalytic oxi-
dation with ozone of benzene. An ozone generator was
used to produce ozone with a concentration of 2000
50 ppm. The ozone flow rate was controlled by a mass flow
controller (MFC, Brooks 5850E) at 60 ml/min. 200 ppm
benzene (N2 balance) was introduced at a flow rate of
Sample
area (m2 g−1
ꢀ
volume (cm3 g−1
ꢀ
MSU-H
820
370
499
225
0.98
0.65
0.58
0.19
MnOx/MSU-H
Meso-SAPO-34
MnOx/Meso-SAPO-34
J. Nanosci. Nanotechnol. 15, 454–458, 2015
455