Promotion of Fe and Co doped Mn-Ce/TiO_2 catalysts for low temperature NH_3-SCR with SO_2 tolerance

摘要

Fe and Co doped Mn-Ce/TiO2 catalysts for low temperature NH3-SCR with SO2 resistance were investigated via in-situ DRIFTS, SO2-TPD and FTIR. The activity results indicated that Fe and Co co-doped catalyst with an Fe/Co molar ratio of 2:4 (2Fe4Co-MCT) showed excellent SO2 resistance (98% NO conversion) at 200 degrees C when compared to the Mn-Ce/TiO2 catalyst. In-situ DRIFTS and SO2-TPD results showed that SO2 reacted with NH3 to form (NH4)(2)SO4 or NH4HSO4 as reversible deactivation blocking the active sites. Moreover, SO2-TPD results further implied that irreversible deactivation of Mn-Ce/TiO2 occurred by SO2 due to the formation of thermal stable sulfated species (MnSO4, Ce(SO4)(2) or Ce-2(SO4)(3)) to reduce active substances. The adsorption characteristics by in-situ DRIFTS revealed that more absorbed SO3, surface sulfite/sulfate and bulk-like sulfate species were formed on Mn-Ce/TiO2 catalyst, while Fe and Co addition to Mn-Ce/TiO2 significantly decreased the sulfur adsorption. The uniform distribution of Fe and Co on the Mn-Ce/TiO2 surface stopped SO2 diffusing to the inner layer of catalyst. In-situ DRIFTS also illustrated that the SCR reaction over 2Fe4Co-MCT catalysts mainly followed by Eley-Rideal (E-R) mechanism in the presence of SO2, which the adsorbed NH3 and NH4+ species reacted with gaseous NO species to produce unstable NH4NO2 and then rapidly decomposed into N-2 and H2O.