The promotional effect of NO on N 2O decomposition over the bi-nuclear Fe sites in Fe/ZSM-5

Abstract

Combining transient response method, steady-state kinetics, in situ IR, and in situ Raman spectroscopic techniques, the effect of NO on N 2O decomposition over Fe/ZSM-5 catalyst was investigated in detail, which reveals that the active sites are bi-nuclear Fe sites. The presence of NO increases the desorption rate of O 2 and lowers the apparent activation energy of N 2O decomposition. Trace amount of water vapor can lead to the deactivation of the Fe/ZSM-5 catalyst due to the oxidation of the active Fe 2+ sites during N 2O decomposition. On the other hand, NO treatment causes the regeneration of the inactive Fe sites by releasing O 2 at relatively low temperature. For the first time, it was found that a Raman band at 743 cm −1, assigned to the bi-nuclear Fe sites, changes accordingly with the deactivation and regeneration of the Fe/ZSM-5 catalyst. The in situ IR spectroscopic study reveals that NO treatment of the deactivated catalyst can remove the hydroxyl groups bound to the inactive Fe 3+ species. These results demonstrate that H 2O and NO play important roles in the structural transformation between the hydroxylated bi-nuclear Fe 3+ sites and the dehydroxylated bi-nuclear Fe 2+ sites in Fe/ZSM-5. Our conclusion is that the positive effect of NO on N 2O decomposition is due to the dehydroxylation of the hydroxylated bi-nuclear Fe sites facilitated by NO, as well as the enhancement of the O 2 desorption rate regulated by NO.