| The NOx in atmoshpere not only affects on human health,but also induces some environmental problems like haze,acid rain and photochemical smog.With the development of economy,the pollution problem resulting from NOx emission is becoming more and more serious.Nowadays,Selective Catalytic Reduction by NH3 is widely used to remove NOx from flue gas.Take natural goethite as precursor,a series of low temperature denitration catalysts were prepared via thermal treatment under 300-800 oC in air atmosphere.The denitration activity,mechanism and kinetic model of catalyst were studied by means of XRD,XRF,XPS,BET,SEM,TEM,TG,NH3-TPD,H2-TPR,FT-IR,in situ DRIFTS and so on.The important conclusions of this work are summarized as follows:?1?The materials got from the thermal treatment of natural goethite were a kind of mesoporous material,in which ?-Fe2O3 and MnOx were the active component,MnOx exists in the form of amorphous state,and Mn2+,Mn3+ and Mn4+ are the three kinds of existence form of manganese element.The structure-function relationship of catalysts showed that MnOx promotes the low-temperature de-NOx reactivity and ?-Fe2O3 ensures lower N2 O selectivity;the specific surface area,pore structure,surface acidity and oxidizability all have great influences on the de-NOx reactivity.?2?H300 exhibited the best activity of denitration,the activity temperature window was 150-300 oC,the biggest NO conversion of 99.77% was obtained at 200 oC.Besides,an increse of mass space velocity led to the decrease of NO conversion and the increase of N2 O selectiviy.An decrease of NH3/NO ratio resulted in the increase of NH3 conversion and the decrease of N2 O selectivity.?3?ER mechanism and LH mechanism occured simultaneously during the detration process of H300.The formation rate of N2 O through ER mechanism was much larger than LH mechanism.The presence of H2 O led to the decrease of k SCR/ER and the increase of kSCR/LH.?4?H2O restrained the de-NOx reactivity of H300 when the reaction temperature was lower than 200 oC,while H2 O promoted the reactivity of H300 when the reaction temperature was higher than 200 oC.Moreover,the effect of H2 O on detration activity was reversible.However,the effect of SO2 on detration activity is irreversible.SO2 restrained the de-NOx reactivity of H300 through three ways: sulfation,competitive adsorption with NH3/NO,and deposition of ammonium sulfate.When H2 O and SO2 existed simultaneously,H2 O expedited the decline of the de-NOx reactivity of H300 by promoting the process of sulfation and the formation and deposition of ammonium sulfate. |
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