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

The reaction between N2O and CH4 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. N2O readily reacted with CH4 in the presence of an N2O+ CH4 mixture above 200degreesC, while both the O-2 + CH4 reaction and the catalytic decomposition of N2O over the Fe-BEA catalyst required higher temperatures (above 400degreesC). In the O-2-TPD studies, a desorption peak of O-2 was observed above 600degreesC after O-2 treatment at 250degreesC, while a new O-2 desorption peak appeared at the lower temperatures after N2O treatment at 250degreesC. However, the new O(a) species resulting from the N2O treatment hardly reacted with CH4 even at 350degreesC, which was confirmed by the CH4-pulsed experiments. On the other hand, a new IR band at 3683 cm(-1), which can be assigned to the OH group on Fe ion species, was observed after O-2 or N2O treatment. The peak intensity at 3683 cm(-1) was not changed in the exposure of CH4 only, but decreased in the exposure of N2O+ CH4 mixture above 150degreesC. At the same time, the CHxOy(a) species such as Fe-OCH3 were formed, which were observed by IR measurements. The adsorbed surface species showed a high reactivity with N2O even at low temperatures (similar to200degreesC). 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 N2O+ CH4 mixture, and may play an important role in the activation/oxidation of CH4 at initial steps to form CHxOy(a) species.