The Effects Of Alkali And Alkaline Earth Ions In Urea Solutions On Cu/SAPO-34 For NH₃-SCR

As its core technology of excellent SCR catalysts,copper ion-exchanged chabazites?Cu/CHA?have been studied extensively due to its outstanding catalytic activity,N₂ selectivity and hydrothermal stability.In addition,the ammonia used in NH₃-SCR reaction comes from the decomposing of urea solution that inevitably contains trace of alkali and alkaline earth ions(e.g.K⁺,Na⁺,Ca²⁺,Mg²⁺).The effects and effect mechanism of alkali and alkaline earth ions(K⁺,Na⁺,Ca²⁺,Mg²⁺)on Cu/SAPO-34 were studied in this work.Cu/SAPO-34 were synthesized using a“one-pot”method.ICP was used to determine M?M:K,Na,Ca,Mg?contents and Cu contents.The M effects on the structure,Cu species,and NH₃-SCR reaction over Cu/SAPO-34 were characterized through XRD,BET,NH₃-TPD,ex-DRIFTS,H₂-TPR,EPR,catalystic performance tests and kinetic experiments,and CO₂-DRIFTS were used to probe the types of Na species.The results indicated that under the fact that the max contacting contents of Cu/SAPO-34 with K?Na?Ca?Mg is 1.0 wt%,among these four ions,only Na⁺has negative effect on Cu/SAPO-34.The effect mechanism was then studied and the results demonstrated that the introduced Na⁺exchanges with H⁺from Si-OH-Al and isolated Cu²⁺of Cu/SAPO-34,and the exchanging of H⁺is easy than that of isolated Cu²⁺.The exchanged H⁺lead to the structure damaging of Cu/SAPO-34 by creating a local acid environment,and the exchanged Cu²⁺aggregates and forms“CuAl₂O₄-like”species.The NH₃-SCR activity decreases with Na contents,the loss of isolated Cu²⁺and acid sites account for the activity loss.