(27c) Transient Isotopic Labeling and in-Situ FT-IR Studies Over Mn/TiO2 Catalysts to Investigate Low Temperature SCR Mechanism of NO with NH3

In recent years, manganese-based catalysts have attracted much attention because of their unique redox (oxidation-reduction cycle) properties make them useful for a variety of applications. Moreover, Mn-based catalysts have been proven as most active catalysts for the low-temperature selective catalytic reduction (SCR) of NO_x. In spite of the rapidly growing commercial applications for the SCR process, the large number of researchers focusing on various aspects of these reactions, there still remains questions about the reaction pathway and the potential intermediate species over these catalysts. For this purpose, the transient isotopic labeling studies were performed under steady state conditions by using ¹⁵N (¹⁵NO and ¹⁵NH₃) and ¹⁸O (¹⁸O₂) containing species to investigate the reaction mechanism of the low temperature SCR of NO over Mn/TiO₂ with NH₃. The results acquired with the time resolution illustrated that the reaction of ammonia with lattice oxygen was practically instantaneous. The formation of labeled N₂¹⁸O, N¹⁸O and H₂¹⁸O species is evident through the NH₃ contact with catalyst surface lattice oxygen but not direct contact with the gas phase oxygen. Furthermore, the sharp decrease of the unlabeled species ¹⁶O¹⁶O response on NH₃ introduction (at t = fraction of minute) is evident of the instantaneous reaction of surface oxygen species with ammonia. The catalytic performance transient labeling and in-situ FT-IR studies over the Mn/TiO₂ material will be discussed in the presentation.