Study On The Reaction Performance Of NH₃-SCR At Low And Middle Temperature Over Modified Mn-based Catalyst

In recent years,Nitrogen oxides in the industry have a harmful impact on the environment.It resulted in more attention to the removal of nitrogen oxides.MnO_x contains various lattice oxygens,and it has a high denitrification activity.But activity temperature window of pure MnO₂ is narrow,furthermore,pure MnO₂ has a poor activity above 300℃ and poor performance of water resistance and SO₂ resistance.So it is of great importance to expand the activity of manganese-based catalysts under different conditions.In the present research,manganese-based catalysts were first used as research object.The active component and environmental factors on catalytic activity were investigated to optimize the reaction performance on a fixed bed reactor.It was found that the introduction of Ce promoted the low-temperature activity of the Mn-based catalysts,and then the effects of O₂ content,NH₃/NO,NO content,airspeed,water vapor and SO₂ on the activity of5Mn-4Ce/Al₂O₃ catalyst were also investigated.It was found that the activity of the catalyst increased with the increase of O₂ content and NH₃/NO molar ratio,and then tends to be flat.With the increase of NO content and airspeed,the catalytic activity gradually decreases.In addition,water vapor and SO₂ have a greater influence on catalyst activity.At 300℃,the ability of resisting SO₂ and water vapor poisoning of Mn-Ce/Al₂O₃ at different water vapor contents increases significantly.The formation of NH₄HSO₄ and metal sulfate on the catalyst surface after SO₂ was added leaded to the loss and coverage of active components,which irreversibly poisoned the catalysts.Then,the effect of support of the catalyst on the catalytic activity of NH₃-SCR was studied.The results show that enhancing acidity of the support is beneficial to the activity of the catalyst above 200℃.After the SO₄^2-and PO₄^3-modification of support,the acid sites of the catalyst is increased,and the activity of the catalysts at 250℃⁴50℃ increase significantly.Moreover,the modified catalysts are used for different temperature.With the increase of acid concentration,the active temperature window migrates to high temperature.Above all,the activity of catalysts with different types of catalyst supports were studied.Mn-Ce/LTB-2 and Mn-Ce/ZSM-5 catalysts exhibit higher activity above 250℃ ascribed to more concentration of acid sites,,and De-NO_x efficiency of above 80%at the reaction temperature range of 150℃⁴00℃,200℃⁴50℃.Expanding the application potential of manganese-based catalysts at 250℃⁴50℃.The change of the catalyst support improves the water resistance of the catalyst at 300℃.Mn-Ce/LTB-2 and Mn-Ce/ZSM-5have better water resistance.The Mn-Ce/LTB-2 catalyst has De-NO_x efficiency of about 70%when it is fed with water vapor and SO₂ simultaneously.Finally,the reaction mechanism of Mn-Ce/Al₂O₃ catalyst under different reaction temperatures was discussed.There are two kinds of reaction paths at 150℃.The first one considered the reaction between NH₂ species and gaseous NO.The other one believed the reaction was attribute to the interaction between weakly adsorbed NH₃ and nitrite.At 300℃,gaseous NO reacts with NH₄⁺.