The Effect Of SO₂Poisoning On The NH₃-SCR Performance Over Cu/SAPO-34Catalysts

The Selective Catalytic Reduction (SCR) is one of the most efficienttechnologies to decrease the NOx in the exhaust gas of stationary and mobile source.Compared with the noble catalysts, oxide catalysts and other zeolites catalysts theCu/SAPO-34is a promising candidate as NH3-SCR catalysts. This paper is focusedon how the SO2posioning affect the structures and the activity of Cu/SAPO-34catalysts, aiming to investigate the SO2posioning mechenism of Cu/SAPO-34catalysts and supply principles for researching and developing new zeolites SCRcatalysts.This study mainly focuses on investigating the influence of SO2poisoning on thestructure and activity of Cu/SAPO-34catalysts during the selective catalytic reductionof NO by NH3(NH3-SCR) and their regeneration ability after desulfuration. The XRD,BET, XRF, ex-DRIFTS, TPR, EPR, SCR activity test and kinetic analysis are used tocharacterize the structure and activity change.Cu/SAPO-34catalysts are treated with different SO2concentrations (112ppmand336ppm) and time (5h and16h) at250oC to obtain SO2poisoned samples. TheSCR results reveal the SO2poisoning could seriously decrease the NO conversionduring the whole temperature range (100oC-500oC). The XRF result shows there isalmost no sulfur existing in the treated SAPO-34support, and the ex-situ DRIFTS andBET expose that the SO2poisoning does not affect its framework structure, while, thecoordination of the isolated Cu2+species (active site of the reaction) in Cu/SAPO-34samples is affected by SO2-treatment from ex-situ DRIFTS. The TPR and EPR resultsfurther confirm the decrease of isolated Cu2+content in the SO2poisoned samples,and cupric sulfate/sulfite may formed. The isolated Cu2+content partially recoveredafter regeneration, leading to the corresponding restoration of NH3-SCR activity.Moreover, the kinetic results demonstrate the SO2poisoning does not influencethe apparent activation energy (Ea) of NH3-SCR reaction over Cu/SAPO-34catalysts.The decline of the NH3-SCR activity is due to the decrease of the active sites. Thetransition from poisoned isolated Cu2+species into CuO species could be one of thereasons for the partial recover after regeneration.