(141c) Catalytic Removal of Volatile Organic Compounds Over the Three-Dimensionally Ordered Mesoporous or Macroporous MOx (M = Co, Fe, Mn, Cr) Catalysts

Catalytic removal
of volatile organic compounds over the three-dimensionally ordered mesoporous or
macroporous MO_x (M = Co, Fe,
Mn, Cr) catalysts

Hongxing
Dai ^a,*, Yunsheng
Xia ^a, Ruzhen Zhang ^a, Lei Zhang ^a, Jiguang Deng
^a, Yingshu Liu ^b, Kai Wang ^c, Hong He ^a,
Jian Li ^a

^a College of Environmental and Energy Engineering,
Beijing University of Technology, Beijing 100124, China. E-mail address: hxdai@bjut.edu.cn.

^b School of Mechanical
Engineering, University of Science and Technology Beijing, Beijing 100083, China

^c School of
Resource and Safety Engineering, China University of Mining & Technology
Beijing, Beijing 100083, China

Most of volatile organic compounds (VOCs) are environmental
pollutants. Catalytic combustion is a
good way for VOCs removal.
The key issue is the availability of an effective catalyst. Recently, we have fabricated
MO_x
(M = Co, Fe, Mn, Cr) with a three-dimensionally (3D) or 3D
ordered macroporous (3DOM) structure
using nitrate of Co, Fe, Mn or Cr as metal source, and found that these materials (see Table 1) exhibited excellent catalytic
activities for the combustion of formaldehyde, acetone, methanol, and toluene^[1].

The
as-fabricated materials were characterized by the XRD, BET, SEM, TEM,
XPS, and H₂-TPR techniques. The typical TEM and SEM images of the samples are shown in
Fig. 1. It is found that the KIT-6- and SBA-16-templating derived samples possessed
ordered mesoporous architectures with crystalline walls. There was formation of nanovoids within the
walls of the 3DOM-structured Fe₂O₃-2 sample.
The surface areas of the mesoporous MO_x (M = Co, Fe, Mn, Cr) samples were above
100 m²/g. XPS analyses revealed the copresence of Co²⁺/Co³⁺ in Co₃O₄, Fe³⁺/Fe²⁺ in Fe₂O₃, and Cr³⁺/Cr⁵⁺/Cr⁶⁺ in CrO_x. Compared
to the corresponding bulk metal oxides, the macro- or mesoporous counterparts exhibited higher surface oxygen species amount and were more reducible
at low temperatures.
The
porous materials showed much better catalytic activities (evaluated with the temperature T_50% and T_90% at VOC conversion = 50 and 90%, respectively) than the bulk
counterparts in VOC combustion (Table 1). The unusual catalytic performance
of the porous transition-metal oxides was related to their better low-temperature reducibility, 3D ordered mesoporous
or
3DOM architecture,
higher
surface oxygen species concentration, and larger surface area.

Table 1. Fabrication methods, pore structures, surface areas (S), and catalytic
activities of the as-prepared catalysts

Reaction conditions: 1000 ppm VOC and space
velocity = 20,000 mL/(g h).

Figure
1. TEM and
SEM images of (a) Co₃O₄, (b) Fe₂O₃-1, (c)
Fe₂O₃-2, (d) MnO₂, (e) CrO_x-1 and (f) CrO_x-2

Reference

1  (a) Y.S. Xia, H.X. Dai, H.Y. Jiang, et al., Environ. Sci.
Technol. 43
(2009) 8355;
(b) Y.S. Xia, H.X. Dai, L. Zhang, et
al., Appl. Catal. B 100 (2010) 229; (c) Y.S. Xia, H.X. Dai, H.Y.
Jiang, et al., Catal. Commun. 11 (2010) 1171; (d) J.G. Deng, L. Zhang, H.X. Dai, et al., J. Phys. Chem. C
114 (2010) 2694; (e) Y.S. Xia, H.X. Dai, H.Y.
Jiang, et al., J. Hazard. Mater. 186 (2011) 84; (f) R.Z. Zhang, H.X. Dai, Y.C. Du, et al., Inorg. Chem. 50 (2011) 2534.