Study On Low Temperature NH₃-SCR Performance And Anti-Alkali Metal Poisoning Mechanism Of Manganese Based Catalyst

Biomass fuel is carbon neutral,and biomass power generation has a broad application prospect under the background of“double carbon”.The emission of biomass flue gas should follow the ultra-low emission standard,and nitrogen oxide is one of the main pollutants in the emission reduction of biomass power plants.NH₃-SCR technology is a widely used and mature nitrogen oxide control technology,its core is the development of high efficiency catalysts.At present,commercial SCR catalysts（V₂O₅-WO₃/TiO₂）have problems such as narrow catalytic temperature window and poor alkali resistance,which are difficult to be applied to the removal of nitrogen oxides from biomass flue gas.Therefore,it is urgent to develop NH₃-SCR catalysts which can be used in denitrification of biomass power plant.In order to alleviate the poisoning effect of high concentration alkali metals in biomass flue gas on SCR catalyst,low-temperature denitrification process is generally adopted in biomass power plants.Mn-based catalyst has excellent SCR performance at low temperature,but alkali metal potassium has significant effect on its performance.Therefore,the mechanism of potassium poisoning on MnO_x-CeO₂ was further studied in this paper.On this basis,the Mn-based catalyst was further optimized.MnO_x/Fe₂TiO₅ with excellent SCR activity and potassium resistance at low temperature was prepared,and its anti-potassium poisoning mechanism was investigated.The main research results of this paper are as follows:（1）Although MnO_x-CeO₂ had excellent SCR activity at low temperature,its anti-potassium poisoning ability was poor.In the presence of potassium,the NO_x conversion and N₂selectivity of MnO_x-CeO₂ decreased significantly.The reduction of NO_x on the surface of MnO_x-CeO₂ mainly follows the Eley-Rideal and Langmuir-Hinshelwood mechanisms,and SCR reaction rate is related to the surface acidity and redox capacity of the catalyst.Potassium can significantly reduce the number of acid sites and the concentration of Mn⁴⁺on the surface of MnO_x-CeO₂,thus inhibiting the adsorption and activation of gaseous NH₃ on the surface of the catalyst.At the same time,potassium can promote the adsorption of NO_x on the surface of MnO_x-CeO₂,and promote the formation of stable nitrate on the surface,which will not react with NH₃ adsorption state,and also inhibit the adsorption of gaseous NH₃ on the catalyst surface.In addition,the increase of surface stabilized NO₃^-concentration can also promote the generation of N₂O,thus increasing the N₂O selectivity of MnO_x-CeO₂.Therefore,potassium has a significant poisoning effect on NH₃-SCR reaction of MnO_x-CeO₂.（2）MnO_x/Fe₂TiO₅ has excellent SCR activity at low temperature,the NO_x conversion rate reaches 95%at 150 ^oC,and the selectivity of N₂O is less than 5%.At the same time,MnO_x/Fe₂TiO₅ showed excellent anti-potassium poisoning ability.In the presence of potassium,the NO_x conversion of MnO_x/Fe₂TiO₅ reaches 85%at 150 ^oC,and the selectivity of N₂O is less than 10%.Since potassium is mainly deposited on MnO_x on the surface of the catalyst,while gaseous NH₃ is mainly adsorbed on Fe₂TiO₅,the introduction of potassium will not significantly reduce the number of acid sites and Fe³⁺concentration on MnO_x/Fe₂TiO₅,and has little impact on the acidity and redox capacity of the catalyst.Therefore,the influence of potassium on the adsorption and activation of gaseous NH₃ on the catalyst surface is also slight.In addition,there is basically no nitrate formation on the surface of MnO_x/Fe₂TiO₅,and the introduction of potassium is difficult to promote the formation of stable nitrate,which will not seriously inhibit the adsorption of gaseous NH₃ on the catalyst surface and promote the generation of N₂O.Therefore,MnO_x/Fe₂TiO₅ shows excellent anti-potassium poisoning ability,which has the potential to be applied in biomass power plant flue gas denitrification.