Study On Water And SO₂ Tolerance Of Metal Oxide Low Temperature NH₃-SCR Catalysts

Low-temperature NH3-SCR(<200℃),which can be located downstream of the electrostatic precipitator and even desulfurizer where most of SO2 and dusts have been removed,has been paid more and more attentions in the past decades.For the wet flue gas desulfurization method used in China,catalytic activity in the presence of SO2 and H2O is an important fact to measure a NH3-SCR catalyst.The most reported Mn-based catalysts usually exhibited excellent low temperature SCR activity whereas poor catalytic performance in the presence of SO2 and H2O.To solve this problem,tries in the following 3 facts were carried out.1.By depositing trace SiO2 onto the surface of Mn-Ti oxide catalyst,the catalysts exhibited enlarged pore size with no compromise of its initial activity.The pore size heavily influenced the catalyst inactivation in the presence of water.The capillarity of water was severely under low temperature,and water condensed in pore of catalysts inhibited the NH3-SCR.Larger pore size prevented more catalyst from water condensation,since water vapor tended to liquefying in small pore.Therefore,the large pore catalyst exhibited higher NH3-SCR activity in the presence of H20.This result shed light on the rational design of NH3-SCR catalysts with enhanced water-tolerance.2.For serious SO2 poisoning character of Mn-based catalyst,we tried to find out a non-Mn catalyst for low temperature NH3-SCR which was difficult to sulfation.A novel CrOx nano-particle catalyst was synthesized by MOF-assisted process,and exhibited superb NH3-SCR activity as Mn-based catalysts.Due to the size effect,unstable lattice oxygen on the surface of CrOx nano-particles exhibited high activity and could oxidize NO to NO2.The formed NO2 participated in NH3-SCR and made reaction on catalysts proceed through a "fast NH3-SCR" pathway,which enhanced the catalytic activity.The stable lattice of Cr oxide made the catalyst immune to sulfation process,which was inferred to be the cause of its superior regeneration ability in the presence of SO2.3.SO2 poisoning mechanism of Mn oxide in the presence of H2O,NH3,and O2 was system studied.It was found that the formation of MnSO4 and the deposit of NH4HSO4 caused the deactivation of Mn oxide in the absence of H2O as it was described in reference.However,in the presence of H2O,MnSO4 would not form.NH4HSO4 is the only reason which caused the SO2 poisoning of Mn oxide.Based on this discovery,a combined catalyst which employed Mn2O3 as SO2 trap was designed and exhibited excellent catalytic activity in the presence of H2O and SO2.