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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

Author:
Guo, Rui-tang, Wang, Shu-xian, Pan, Wei-guo, Li, Ming-yuan, Sun, Peng, Liu, Shu-ming, Sun, Xiao, Liu, Shuai-wei, Liu, Jian
Source:
The Journal of Physical Chemistry C 2017 v.121 no.14 pp. 7881-7891
ISSN:
1932-7455
Subject:
X-ray diffraction, X-ray photoelectron spectroscopy, adsorption, ammonia, catalysts, chemical reduction, crystallization, magnesium, nitric oxide, nitrogen, oxidation, oxygen, physicochemical properties, potassium, titanium dioxide
Abstract:
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.
Agid:
5678249