Preparation And Study On MnO_x-TiO₂ Denitration Catalysts Modified By Fe And Ce

NOx is one of the main air pollutants and selective catalytic reduction is an effective way to remove NOx in the flue gas from stationary sources.The high temperature selective catalytic is the most widely used way in reduction denitration process.However,the vanadium-titanium catalyst discarded produced by the process is a toxic solid waste,which can cause secondary pollution to the environment.Recently,low-temperature selective catalytic reduction has attracted more and more interests by institutors for its low energy consumption and operating cost.The research shows that the main obstacles of the low temperature selective denitration technology are the low activity at low temperature and poor SO₂ resistance.In order to solve these problems,MnOx-TiO₂ catalyst was studied to improve its low-temperature denitrification activity.Firstly,Fe and Ce single metal was chosen to be doped into MnOx-TiO₂ catalyst.From activity tests and characterization（XRD,BET,XPS,H2-TPR,NH3-TPD）results on series of catalysts,it was found that Ce doping and Fe doping all could greatly enhance the low-temperature selective catalytic reduction activity in the catalyst,the NOx conversion rate of 0.08Fe/MnOx-TiO₂ and 0.05Ce/MnOx-TiO₂ could achieve 90%at 105℃.The oxygen storage capacity,the specific surface area and the surface acidity of MnOx-TiO₂ catalyst were improved by the introduction of Ce or Fe,which would promote the adsorption and activation of NH3.Secondly,Fe and Ce doped at the same time modified in MnOx-TiO₂ catalyst.The activity of these catalyst were tested,it was found that,the simultaneous doping of Fe and Ce could further improve the catalyst’s low-temperature activity.The NOx conversion rate of 0.05Ce0.08Fe/MnOx-TiO₂ was 90%at 99℃.Through the XRD and BET analysis of 0.05Ce0.08Fe/MnOx-TiO₂,we found that the dispersibility of the active component on the TiO₂ support and the specific surface area increased;XPS analysis showed that the chemisorbed oxygen on the catalyst surface increased.Mn existed in the form of MnO₂ and Mn2O₃,Ce and Fe promoted the conversion between MnO₂ and Mn2O₃,facilitated the denitration reaction;the results of H2-TPR and NH3-TPD showed that the content of weak acid and medium strong acid on the surface of the catalyst increased,and the low temperature redox ability increased.The effect of SO₂ on the selective catalytic reduction activity was also investigated.Results showed that a serious deactivation by SO₂ was detected on MnOx-TiO₂ and 0.08Fe/MnOx-TiO₂ catalysts,and 0.05Ce/MnOx-TiO₂ catalyst deactivation rate was relatively slow.And 0.05Ce0.08Fe/MnOx-TiO₂ catalyst always maintained 90%rate of NOx conversion.Which indicate that Ce doping could decrease the stability of the formed sulfate species,and multi-metal doping could improve the anti-SO₂ performance of the catalyst.Through this research,we prepared a kind of MnOx-TiO₂ catalyst doped with Fe and Ce,compared with the existing low-temperature denitration catalyst,which had high low-temperature activity and strong resistance to SO₂ poisoning.It provided the basis for industrial application of low temperature selective catalytic reduction denitration process.