Study on MnO x -FeO y composite oxide catalysts prepared by supercritical antisolvent process for low-temperature select
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In this study, the MnOx–FeOy hollow nanospheres with solid solution structure were prepared by supercritical antisolvent (SAS) process. The average particle size was about 50 nm, and average pore diameter was 7 nm. By applying the SAS method, novel nonsupported MnOx–FeOy catalysts with a Mn/Fe mass ratio of 1:1 showed rather high selective catalytic reduction activity and broad active temperature window. The NOx conversion rate reached 97% at 220 °C, and maintained above 92% from 180 to 260 °C. The experiment results showed that iron doping could cause the apparent change of MnOx morphology and structure, which enhanced the oxidative ability of manganese species and increased surface active oxygen species. Meanwhile, compared with traditional methods, the SAS process could efficiently enhance the interaction between manganese and iron, and produce smaller size and larger pore volume nanoparticles with more active sites on the surface.
I. INTRODUCTION
It is well known that nitrogen oxides (NOx) are harmful air pollutants, which cause serious damage to the environment, such as photochemical smog, acid rain, ozone depletion, and greenhouse effects. The selective catalytic reduction of NOx with NH3 (NH3-SCR) is an effective approach to remove NOx contaminants, and highly effective catalyst is the key to carry out NH3-SCR reaction. Currently, V2O5/TiO2 catalysts are commercially available with operating temperature from 300 to 400 °C.1 Although the vanadium based catalysts have relatively high SCR activity and ideal resistance to sulfur poisoning, they can be easily deactivated at high concentration of SO2 and ash in the flue gas, and some side reactions can be triggered at high temperatures to cause the decrease of N2 selectivity.2,3 Many efforts have been devoted to develop new types of SCR catalysts with low active temperature, such as activated carbon supported manganese-based monolithic catalyst (MnOx/AC) prepared by impregnation method,2 mesoporous silica supported iron–manganese composite oxides (Mn–Fe/MPS) prepared by impregnation method,4 and nonsupported manganese–cerium composite oxides (MnOx–CeO2) prepared by supercritical Contributing Editor: Sanjay Mathur a) Address all correspondence to this author. e-mail: [email protected] A previous error in this article has been corrected, see 10.1557/ jmr.2016.117. DOI: 10.1557/jmr.2016.51 702
J. Mater. Res., Vol. 31, No. 6, Mar 28, 2016
http://journals.cambridge.org
Downloaded: 17 May 2016
antisolvent (SAS) process.5 It was reported that the Mn–Fe composite oxide catalyst showed good SCR activity, high N2 selectivity and ideal resistance to water and sulfur poisoning at low temperature. Lin et al.3,4,6,7 have found that the addition of Fe promoter could enhance the number and strength of Brönsted and Lewis acid sites on the surface of Mn-based catalysts, and promote the adsorption of NH3 to form some active intermediates, which improved the NH3-SCR performance at low temperature. Furthermore, the mechanism of NH3-SCR reaction has been investigated by Yang et al. who
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