Reaction between N2O and CH4 over Fe ion-exchanged BEA zeolite catalyst: A possible role of nascent oxygen transients from N2O

Abstract

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.

Preparation and Pretreatment Temperature Influence on Iron Species Distribution and N2O Decomposition in Fe–ZSM-5

“…Chen et al [5] have reported that the hydroxyl group stretching over binuclear iron species in Fe-ZSM-5 prepared by sublimation method at 3665 cm )1 . Hydroxylated iron species are also observed by Mauvezin et al [31] and Kameoka et al [43] in Fe-BEA and by Wood et al [11] in Fe/ AlZSM-5. Wood et al [11] have attributed the observed IR bands at 3680 and 3628 cm )1 to symmetric and asymmetric stretching vibrations of isolated iron species having two hydroxl groups (-Fe(OH) 2 ).…”

Effect of Oxygen Concentration in NH₃-SCR Reaction over Fe- and Cu-loaded Beta Zeolites

“…Low reaction orders of O2 are often observed for catalysts on which the loaded metal is easily oxidized or onto which O2 can easily adsorb. Taking into account the results of O2-TPD reported in the literature 29), 30) and the standard enthalpy change of formation of metal oxides, Fe species adsorb O2 more strongly and tend to be oxidized more easily than Cu species, suggesting a lower reaction order of O2 for the Fe/zeolite catalyst. However, the opposite phenomenon was observed in the present work.…”

A comprehensive investigation of influences of NO and O2 on N2O-SCR by CH4 over Fe-USY zeolite

“…However, to our knowledge, recent studies about N 2 O-CH 4 SCR are mostly focused on Fe-Beta and Fe-MFI catalysts to understand the CH 4 activation mechanism in N 2 O-SCR [25][26][27][28], and there is no report about how SCR of N 2 O by CH 4 is affected by the co-existence NO, O 2 and/or H 2 O that are inevitably present in the N 2 O emission site, such as the nitric acid and adipic acid factories. Although most zeolite catalysts suffer the activity loss during the operation under these practical conditions, we have luckily found that Fe-USY zeolite shows a high activity and a high hydrothermal stability for N 2 O decomposition in our previous studies under the similar conditions [11,12].…”