Preparation Of Catalyst For Selective Catalytic Reduction Of NO_x At Low Temperature And Its Numerical Simulation

Recently, with the significant development of society, air pollutionresulted from NO_xemission become more and more serious and NO_xhasbeen one of the most harmful air pollutants in China.In this work, modified Yoldas-oil-drop method was used to prepareγ-Al₂O₃granules with high specific area, crush strength and attritionresistance. A novel catalyst with high performance for selec tive catalyticreduction （SCR） of NO_xat low temperature for a long time and goodresistance to SO₂poisioning was prepared and optimized employing theTaguchi method. This catalyst named Fe_0.05Mn_0.09Ce_0.05O_x/γ-Al₂O₃consistsof complex oxide derived from Fe, Mn and Ce as active component and theprepared γ-Al₂O₃as supporter. The SEM, BET, XRD and Closed MonolayerModel was used to characterize this catalyst for physical and chemicalproperties. And then, the steady-state kinetics of the selective catalyti creduction of NO with NH₃over Fe_0.05Mn_0.09Ce_0.05O_x/γ-Al₂O₃catalyst at lowtemperature were studied using self-designed eight-channel tubular quartzreactor and nonlinear optimum parameter estimation. In the end, COMSOLMultiphysics was used for the numerical simulation of the selectivecatalytic reduction of NO_xover the monolithic catalysts.Some important results were abtained.（1） The optimum catalyst in thisresearch consisted of5wt.%Fe,9wt%Mn and5wt%Ce of the weight ofγ-Al₂O₃respectively and was calcinated at500℃. The NO removalefficiency could be88.85%at the temperature of150℃when theconcentration （v/v） of NH₃, NO and O₂was1000ppm,1000ppm and5%respectively. And when the temperature was improved to170℃, theremoval efficiency of NO was able to exceed98%.（2） This catalyst hasgood resistance to SO₂and could work for a long time. For instance, at150℃， with the NO concentration as1000ppm, this catalyst was able towork with the removal efficiency higher than85%for30hours and with theremoval efficiency higher than75%when50ppm SO₂was introduced intothe gas flow. Particularly, the deactivation of this catalyst resulted fromSO₂was partially reversible.（3） Rate equation which was based on a powerrate function with the reaction orders of NH₃, NO and O₂as0,0.87and0.44respectively have been derived. The pre-exponential factor k0and apparent activation energy Ea of this reaction was2.550706×10-2mol/(kg·s·Pa^1.31)and41541.616J/mol respectively.（4） The numerical simulation results ofthe selective catalytic reduction of NO_xover the monolithic catalystsshowed that the NO removal efficiency would be improved with theincreasing thickness of the washcoat layer when the thickness was less than0.1mm. While, along with the gas flow in the monolithic catalyst channel,the effective catalyst in the washcoat become more and more thin.（5）According to simulation results, the prepared Fe_0.05Mn_0.09Ce_0.05O_x/γ-Al₂O₃catalyst was suitable for low temperature and low dust （tail-end）arrangement and the diameter of monolithic catalyst channel shoud be in therange of3mm⁴mm. The washco at of monolithic catalyst could be0.02mmwhile at this time, the velocity of gas flow should be less than4.2m/s.（6）Different method for improving the NO removal efficiency under variousconditions have been developed according to analysis of the concentrationdistribution of NO in the monolithic catalyst channel.