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

Guo, Rui-tang, Wang, Shu-xian, Pan, Wei-guo, Li, Ming-yuan, Sun, Peng, Liu, Shu-ming, Sun, Xiao, Liu, Shuai-wei, Liu, Jian
The Journal of Physical Chemistry C 2017 v.121 no.14 pp. 7881-7891
X-ray diffraction, X-ray photoelectron spectroscopy, adsorption, ammonia, catalysts, chemical reduction, crystallization, magnesium, nitric oxide, nitrogen, oxidation, oxygen, physicochemical properties, potassium, titanium dioxide
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 N₂ adsorption, XRD, XPS, H₂-TPR, NH₃-TPD, and NO-TPD 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/TiO₂–Mg was mainly controlled by the L–H mechanism (≤150 °C) and E–R mechanism (>200 °C), while the NH₃–SCR reaction over Mn/TiO₂–K mainly followed the E–R pathway. The deactivation of Mn/TiO₂–Mg mainly resulted from the inhibited adsorption and oxidation of NO, and the seriously suppressed adsorption of NH₃ species made a great contribution to the deactivation of Mn/TiO₂–K.