Takeshi Nobukawa

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 200 °C, while both the O2 + CH4 reaction and the catalytic decomposition of N2O over the Fe-BEA catalyst required higher temperatures (above 400 °C). In the O2-TPD studies, a desorption peak of O2 was observed above 600 °C after O2 treatment at 250 °C, while a new O2 desorption peak appeared at the lower temperatures after N2O treatment at 250 °C. However, the new O(a) species resulting from the N2O treatment hardly reacted with CH4 even at 350 °C, 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 O2 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 150 °C. 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 (∼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 N2O + CH4 mixture, and may play an important role in the activation/oxidation of CH4 at initial steps to form CHxOy(a) species.

Isotopic Study of N2O Decomposition on an Ion-Exchanged Fe-Zeolite Catalyst: Mechanism of O2 Formation

N2O decomposition on an ion-exchanged Fe-MFI catalyst has been studied using an 18O-tracer technique in order to reveal the reaction mechanism. N216O was pulsed onto an 18O2-treated Fe-MFI catalyst at 693 K, and the O2 molecules produced were monitored by means of mass spectrometry. The 18O fraction in the produced oxygen had almost half the value of that on the surface oxygen, and 18O18O was not detected. The result shows that O2 formation proceeds via the Eley–Rideal mechanism (N216O + 18O(a) → N2 + 16O18O).

Enhancement of C2H6 Oxidation by O2 in the Presence of N2O over Fe Ion-Exchanged BEA Zeolite Catalyst

Selective catalytic reduction (SCR) of N2O with C2H6 took place effectively over Fe ion-exchanged BEA zeolite catalyst (Fe-BEA) even in the presence of excess oxygen. The mechanism in the SCR of N2O with C2H6 over Fe-BEA catalyst was studied by a transient response experiment and an in situ DRIFT spectroscopy. No oxidation of C2H6 by O2 took place below 350 °C (in C2H6/O2). In the N2O/C2H6/O2 system, however, it was found that the reaction of C2H6 with O2 was drastically enhanced by the presence of N2O even at low temperatures (200-300 °C). Therefore, it was concluded that N2O played an important role in the oxidation of C2H6 (i.e., activation of C2H6 at an initial step). On the basis of these findings, the mechanism in the SCR of N2O with C2H6 is discussed.

Selective catalytic reduction of N2O with light alkanes and N2O decomposition over Fe-BEA zeolite catalysts

Fe ion-exchanged zeolite catalysts (Fe-BEA, Fe-MFI) were found to be active for selective catalytic reduction (SCR) of N 2 O with light alkanes ( i.e. , CH 4 and C 2 H 6 ) even in the presence of excess oxygen. In the N 2 O/C 2 H 6 /O 2 system over Fe-BEA catalyst, N 2 O plays an important role in the oxidation of C 2 H 6 ( i.e. , activation of C 2 H 6 at an initial step). H 2 -TPR and catalytic measurements of Fe-BEA catalysts with different Fe contents revealed that the active sites for SCR of N 2 O with CH 4 and N 2 O decomposition are Fe ion species, and Fe oxide aggregates are inactive. In O 2 -TPD studies, we observed new desorption peaks from Fe-BEA catalyst after N 2 O treatment. In the isotopic tracer study of N 2 O decomposition, the result shows that O 2 formation on Fe-MFI catalyst proceeds via Eley-Rideal mechanism, which is different from the case of supported Rh catalysts.

Selective catalytic reduction of N2O with CH4 and N2O decomposition over Fe-zeolite catalysts

Abstract The reaction mechanisms of selective catalytic reduction (SCR) of N 2 O with CH 4 and N 2 O decomposition over Fe ion-exchanged zeolite catalysts (Fe-BEA, Fe-MFI) were studied. In O 2 -TPD studies, we observed new desorption peaks from Fe-BEA catalyst after N 2 O treatment. However, the new adsorbed oxygen species hardly reacted with CH 4 . This indicates that coexistence of N 2 O and CH 4 is necessary for the high SCR activity. In infrared (FTIR) spectroscopy, most of Fe-OH species (the OH group on Fe ion species) took part in the N 2 O+CH 4 reaction, and the methoxy and formate species were formed. The methoxy species were oxidized with N 2 O more rapidly than O 2 , while the formate species were oxidized with both N 2 O and O 2 at almost the same rate. The isotopic tracer study using 18 O(a) showed that O 2 formation during N 2 O decomposition proceeds via Eley-Rideal (ER) mechanism. A possible mechanism is discussed in terms of active oxygen species formed from N 2 O, which may play an important role in the activation/oxidation of CH 4 at initial steps.

30-P-11-Selective catalytic reduction of N2O with light alkanes over different Fe-zeolite catalysts

Publisher Summary This chapter presents the selective catalytic reduction of nitrous oxide (N 2 O) with light alkanes over different iron (Fe)-zeolite catalysts. Fe ion-exchanged zeolite catalysts effectively perform selective catalytic reduction (SCR) of N 2 O with light alkanes even in the presence of excess oxygen. Methane (CH 4 ) reacts selectively with N 2 O even in the presence of excess oxygen (O 2 ) while the reaction of ethane (C 2 H 6 ) and propane (C 3 H 8 ) with O 2 is drastically enhanced by the presence of N 2 O. N 2 O plays an important role in the activation of alkanes at an initial step. Based on these results, a mechanism is proposed in the SCR of N 2 O with light alkanes over Fe-BEA catalyst.