Different Poisoning Effects of K and Mg on the Mn/TiO2 Catalyst for Selective Catalytic Reduction of NOx with NH3: A Mechanistic Study

It is well recognized that both alkali and alkali earth metals have a poisoning effect on selective catalytic reduction (SCR) catalyst. In this study, the different poisoning effects of K and Mg on Mn/TiO2 catalyst were investigated. It was found that the deactivation effect of K was much stronger than that of Mg. The effect of K or Mg addition on the physicochemical properties of Mn/TiO2 catalyst was investigated based on N-2 adsorption, XRD, XPS, H-2-TPR, NH3TPD, and NO-PD techniques. The results indicated that the addition of K or Mg on Mn/TiO2 catalyst would decrease its specific area, promote the crystallization of TiO2, and lead to a decrease of Mn4+ and surface chemisorbed oxygen. Furthermore, the presence of K or Mg on Mn/TiO2 catalyst would lead to the drop of reducibility and the adsorption capacity of NH3 and NOx species. In addition, the adsorption behavior of NH3 and NOx and their surface reactions over the fresh and poisoned Mn/TiO2 catalysts were investigated by in situ DRIFT study. It was found that the NH3 SCR reaction over Mn/TiO3Mg was mainly controlled by the L-H mechanism (<= 150 C degrees) and E-R mechanism (>200 degrees C), while the NH3CR reaction over Mn/TiO2 K mainly followed the E-R pathway. The deactivation of Mn/TiO3Mg mainly resulted from the inhibited adsorption and oxidation of NOx and the seriously suppressed adsorption of NH3 species made a great contribution to the deactivation of Mn/TiO2-K.