Study On The MnO_x-FeO_y Composed Oxide Catalysts Prepared By SAS Process For Low Temperature NH₃-SCR

Nitrogen oxides (NOx) are one of the major pollutants for human society, can causeserious damage to both environment and human health. The emission of NOxfrompower plants takes majority in China, therefore the deNOxprocess of power plants hasbeen paid great concern. Selective catalytic reduction with NH3is the most effectiveand economic method to reduce the NOx, while Mn-based catalysts show excellentcatalytic activity for the selective catalytic reduction (SCR) at low temperature, andthe iron doping can improve the catalytic activity and the sulfur and water resistances.In this paper, the MnOx-FeOyhollow nano-spheres catalysts are synthesized viasupercritical anti-solvent process (SAS). A series of characterizations and tests for theprepared catalyst samples are carried out to reveal the effects of the iron doping andcalcination process on the structure and performances of MnOx-FeOycomposed oxidecatalysts.The MnOx-FeOyhollow nano-sphere particles with solid solution structure areprepared by SAS process successfully. It is indicated that SAS process can efficientlypromote the mutual dispersion between MnOxand FeOycomponents, and enhancedtheir interaction,thus the solid solution structure is easily formed. The stronginteraction between the doped Fe and Mn components can result in not only thecrystal phase transformation of MnOx, but also promote the change in Mn valencestates, and thus the number of surface active oxygen species and lattice defects isenhanced, the reduction performance of catalysts is improved, and more Br nsted andLewis acidic sites are formed. Therefore, the novel MnOx-FeOycatalysts show highercatalytic SCR activity and rather broad active temperature window.Through the investigation on effects of calcination temperatures on structure andperformances, it is found that the calcination process can promote the transformationof MnOxcrystal phases, and play an important role in the formation of MnOx-FeOysolid solution structure. The synergic effect between the Fe3+doping and the selfredox process of Manganese oxides with the increased temperature could contribute tostabilize the Mn4+valence state on the surface of MnOx-FeOycomposed oxides. Whenthe calcination temperature is500oC, the prepared MnOx-FeOycatalysts show moreBr nsted and Lewis acidic sites and better reduction performance, and thus, exhibitethe best catalytic SCR activity: the NO conversions are maintained above92%at the temperature range between180°C and260°C, the largest NO conversion at220℃could reach97%, and the biggest N2selectivity is almost100%.