The reaction between N 2 O and CH 4 over an Fe ion-exchanged BEA zeolite (Fe-BEA) catalyst was studied by using a pulse reaction technique, temperature-programmed desorption (TPD) and infrared (IR) spectroscopy. N 2 O readily reacted with CH 4 in the presence of an N 2 O + CH 4 mixture above 200 C, while both the O 2 + CH 4 reaction and the catalytic decomposition of N 2 O over the Fe-BEA catalyst required higher temperatures (above 400 C). In the O 2 -TPD studies, a desorption peak of O 2 was observed above 600 C after O 2 treatment at 250 C, while a new O 2 desorption peak appeared at the lower temperatures after N 2 O treatment at 250 C. However, the new O(a) species resulting from the N 2 O treatment hardly reacted with CH 4 even at 350 C, which was confirmed by the CH 4 -pulsed experiments. On the other hand, a new IR band at 3683 cm À1 , which can be assigned to the OH group on Fe ion species, was observed after O 2 or N 2 O treatment. The peak intensity at 3683 cm À1 was not changed in the exposure of CH 4 only, but decreased in the exposure of N 2 O + CH 4 mixture above 150 C. At the same time, the CH x O y (a) species such as Fe-OCH 3 were formed, which were observed by IR measurements. The adsorbed surface species showed a high reactivity with N 2 O even at low temperatures ($200 C). A possible mechanism is discussed in terms of active oxygen species such as nascent oxygen transients (O*(a)), which are formed in the exposure of N 2 O + CH 4 mixture, and may play an important role in the activation/oxidation of CH 4 at initial steps to form CH x O y (a) species.
The selective catalytic reduction (SCR) of N2O with CH4 in the absence and presence of excess O2 has been
studied over ion-exchanged Fe−BEA catalyst by the combination of an activity test with in-situ infrared
spectroscopy to understand the nature of the surface species involved in the SCR of N2O with CH4. From the
results of flow reaction studies, the Fe−BEA catalyst exhibited high activity in the SCR of N2O with CH4,
even in the presence of excess oxygen, which demonstrates that the active Fe species for the SCR are formed
on the ion-exchanged Fe−BEA catalyst. In the FTIR spectra of fresh catalysts, the OH band on Fe ion species
(Fe−OH) was observed on the Fe−BEA catalyst, and the Fe−OH species can be involved in the SCR of
N2O with CH4. Furthermore, the reaction intermediates of methoxy and formate species over the Fe−BEA
catalyst were observed during the reaction. We measured the oxidation rates of these surface species with
N2O and O2, and found that the methoxy species were oxidized with N2O more rapidly than O2, while the
formate species were oxidized with both N2O and O2 at almost the same rate. On the basis of these results,
we discuss the reaction mechanism of the SCR of N2O with CH4.
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