Preparation,Characterization And Performance Of Nb,Ta Doped Oxides For Selective Catalytic Reduction Of NO

Nitrogen oxides（NO_x）are main air pollutants causing photochemical smog,acid rain,ozone depletion and greenhouse effects.Among various NO_x control technologies,selective catalytic reduction of NO_x with NH₃（NH₃-SCR）has been demonstrated as the most efficient one.Therein,the key point of this technology is the catalyst.Nowadays,the most widely used NH₃-SCR catalyst is V2O5-WO3/TiO2.However,some disadvantages are unavoidable,such as the toxicity of vanadium,the poor activity at temperatures lower than 350 oC,which limited the application widely in industrial furnaces.Consequently,it is important to develop novel environmentally friendly SCR catalysts with high activity and selectivity to remove NO_x.In this paper,a series of Nb-doped iron oxides NH₃-SCR catalysts were prepared by co-precipitation method.Their physicochemical properties were studied by X-ray powder diffraction（XRD）,N₂ adsorption-desorption,inductively coupled plasma atomic emission spectrometry（ICP-AES）,transmission electron microscope（TEM）,X-ray absorption fine structure（XAFS）,H2 temperature programmed reduction（H2-TPR）and NH₃ temperature programmed desorption（NH₃-TPD）.The results show that the phases of FeNbO4 and Nb-doped Fe2O3 coexist in Nb-doped iron oxides.However,only the latter one contributes to the improvement of specific surface areas,redox and acidity properties,which are responsible for the excellent catalytic activity.It is clearly seen that the optimal composite was obtained when 30.3 wt.% of Nb was added,which exhibits nearly 100% NO conversion and the excellent resistantance performance for SO2 and H2 O.Besides,a series of Ta-doped iron oxides as NH₃-SCR catalysts were prepared by methods of co-precipitation,citric acid and impregnation,respectively.By comparison,it can be found that the Ta-doped iron oxides prepared by the impregnation method can effectively improve the low temperature DeNO_x catalytic activity.The results of XRD,BET,H2-TPR and NH₃-TPD indicated that Ta is highly dispersed on the surface of Fe2O3.What’s more,the excellent NH₃-SCR performance is intrinsically attributed to the combined effects of specific surface area,redox capacity and the acidity.