Short communicationLow-temperature selective catalytic reduction of NO with NH3 over ordered mesoporous MnxCo3 − xO4 catalyst
Graphical abstract
Introduction
Nitrogen oxides (NOx) derived from power plant and vehicle exhausts have resulted in serious atmospheric environment pollutions nowadays, such as ozone depletion, photochemical smog and acid rain [1], [2]. Selective catalytic reduction (SCR) of NOx with NH3 is an effective technology to reduce NOx emissions [3], [4]. Nowadays V2O5–WO3/TiO2 is the most widely used catalyst. However, there are some inevitable problems that remain in this catalyst, such as the toxicity of vanadium, SO2 oxidation to SO3, and the need to operate at high temperatures (300–400 °C). Thus, it is urgent to develop low-temperature (LT) SCR catalysts, which could be located downstream of the electrostatic precipitator and desulfurization.
Recently, it has been reported that transition metal oxides (e.g. Cr2O3, Co3O4, CuO, or MnO2) show good activity for LT-SCR reaction [5], [6], [7]. Among all metal oxides studied, manganese and cobalt containing catalysts are low cost, environmentally friendly and relatively highly active for NO reduction. However, they are very sensitive to the presence of SO2 in the exhaust, and the temperature window is narrow and not suitable to practical application. Appropriate combinations of metal oxides may exhibit higher activity and thermal stability than the single oxides [8], [9], [10], [11]. The traditional nanoparticles could agglomerate easily during the catalytic process, resulting in the decline of catalytic activity. Compared to the nanoparticles, the ordered mesoporous materials with large surface-to-volume ratios and uniform porous structure exhibit many interesting properties in energy conversion and storage, catalysis, sensing and magnetic devices because they possess d-shell electrons confined to nanosized walls, redox active internal surfaces, and connected pore networks [12], [13].
Herein, in this paper, a highly ordered mesoporous MnCo2O4 was synthesized via the nanocasting method. The synthesis of mesoporous metal oxides via the nanocasting route can deliver materials with highly ordered pore structures and highly crystalline walls, as well as good thermal stability. The MnCo2O4 catalyst exhibited ultra-high low temperature catalytic activity for cleaning NO with NH3 from 100 to 300 °C. The major reasons were studied.
Section snippets
Synthesis of samples
The porous silica template with cubic (Ia3d) pore symmetry (KIT-6) was synthesized according to the previous literature [14]. In a typical synthesis process, 1.0 g KIT-6 was suspended in 70 mL dry n-hexane, then stirred for 3 h, and 1.0 mL aqueous solution containing 2.3 mmol Mn(NO3)2·4H2O and 4.6 mmol Co(NO3)2·6H2O were added with vigorous stirring. The mixture was stirred overnight, filtered and dried at 40 °C, then calcined in a muffle furnace at 450 °C for 4 h with a heating rate of 1 °C/min.
Results and discussion
The XRD patterns of the sample were shown in Fig. 1. The diffraction peaks of single Co3O4 and MnO2 could be ascribed to cubic spinel phase Co3O4 (JCPDS 74-2120) and pyrolusite-MnO2 (JCPDS 81-2261). For the MnCo2O4 sample, the diffraction peaks that belonged to the face-centered-cubic (fcc) space group (Fd-3m(227); JCPDS 23-1237) could be observed. According to the Scherrer Formula, the grain sizes of Co3O4, MnO2 and MnCo2O4 were 12.4, 11.1 and 8.9 nm, respectively. From low-angle XRD patterns
Conclusions
In summary, we have successfully fabricated mesoporous MnCo2O4 with a spinel structure via the nanocasting route, for the low temperature NH3-SCR. Compared to the single metal oxide, MnO2 and Co3O4, the MnCo2O4 catalyst exhibits an enhanced NH3-SCR activity, high N2 selectivity, wide operating temperature window, and improved SO2 tolerance. The outstanding NH3-SCR activity of the MnCo2O4 catalyst can be attributed to the strong interaction of manganese and cobalt oxide species as well as the
Acknowledgment
This study was financially supported by the National Natural Science Foundation of China (21377061 and 81270041), the Asia Research Center in Nankai University (AS1326), the Natural Science Foundation of Tianjin (12JCQNJC05800), and the Key Technologies R&D Program of Tianjin (13ZCZDSF00300).
References (20)
- et al.
TNU-9, a new zeolite for the selective catalytic reduction of NO: An in situ X-ray absorption spectroscopy study
J. Catal.
(2012) - et al.
Influence of sulfation on iron titanate catalyst for the selective catalytic reduction of NOx with NH3
Appl. Catal. B Environ.
(2011) - et al.
Mesoporous MCo2O4 (M = Cu, Mn and Ni) spinels: structural replication, characterization and catalytic application in CO oxidation
Microporous Mesoporous Mater.
(2009) - et al.
MnxCo3 − xO4 solid solution as high-efficient catalysts for low-temperature oxidation of formaldehyde
Catal. Commun.
(2012) - et al.
Cu–Mn and Co–Mn catalysts synthesized from hydrotalcites and their use in the oxidation of VOCs
Appl. Catal. B Environ.
(2011) - et al.
Synthesis of light alkenes from syngas on silicalite-1 supported cobalt and cobalt–manganese catalysts
Appl. Catal. A Gen.
(1995) - et al.
Highly dispersed CeO2 on carbon nanotubes for selective catalytic reduction of NO with NH3
Catal. Sci. Technol.
(2013) - et al.
Effects of hydrocarbons and water vapor on NOx-using V2O5–WO3/TiO2 catalyst reduction in combination with nonthermal plasma
Ind. Eng. Chem. Res.
(2007) - et al.
Design of meso-TiO2@MnOx–CeOx/CNTs with a core–shell structure as DeNOx catalysts: promotion of activity, stability and SO2-tolerance
Nanoscale
(2013) - et al.
Porous Ni–Mn oxide nanosheets in situ formed on nickel foam as 3D hierarchical monolith de-NOx catalysts
Nanoscale
(2014)
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