Characterization and performance of common alkali metals and alkaline earth metals loaded Mn/TiO2 catalysts for NOx removal with NH3

Abstract

The influence of four common alkali metals and alkaline earth metals (Na, K, Mg and Ca) on Mn/TiO2 catalysts for selective catalytic reduction of NOx with NH3 was investigated. K, Na and Ca deactivated the catalysts and the deactivation effects were shown in sequence as K > Na > Ca, while Mg improved the capability of the catalysts. Furthermore, physical and chemical properties of catalysts were characterized by XRD, H2-TPR, NH3-TPD, BET, FESEM, XPS, TG and in situ DRIFTS analyses. Characterization results suggested that the obvious decrease of NH3 adsorption and surface redox ability and the formation of inactive compounds could take credit for the deactivation caused by alkali metals and alkaline earth metals except Mg. The atomic concentrations of Mn3+ and relative concentration ratios of Oα/(Oα+Oβ) on the surfaces were also important factors for SCR activities of Mn/TiO2 catalysts doped with the main group IA elements (Na and K). The in situ DRIFTS tests further confirmed that the alkaline size resulted in the considerable changes in the desorption strength of ammonia which was in accordance with the NH3-TPD results. Meanwhile, the slight decrease of NH3 adsorption and surface redox ability and the formation of MgMn2O4 appeared to be directly correlated with the better SCR performance of the catalysts doped with Mg. Moreover, acid site and redox site played important roles in the catalytic cycle for Mn/TiO2 catalysts during the NH3-SCR reaction.