The promotional effect of NO on N2O decomposition over the bi-nuclear Fe sites in Fe/ZSM-5

Combining transient response method, steady-state kinetics, in situ IR, and in situ Raman spectroscopic techniques, the effect of NO on N2O 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 O2 and lowers the apparent activation energy of N2O decomposition. Trace amount of water vapor can lead to the deactivation of the Fe/ZSM-5 catalyst due to the oxidation of the active Fe2+ sites during N2O decomposition. On the other hand, NO treatment causes the regeneration of the inactive Fe sites by releasing O2 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 Fe3+ species. These results demonstrate that H2O and NO play important roles in the structural transformation between the hydroxylated bi-nuclear Fe3+ sites and the dehydroxylated bi-nuclear Fe2+ sites in Fe/ZSM-5. Our conclusion is that the positive effect of NO on N2O decomposition is due to the dehydroxylation of the hydroxylated bi-nuclear Fe sites facilitated by NO, as well as the enhancement of the O2 desorption rate regulated by NO.

Graphical abstractNO promotes the transformation of hydroxylated into active binuclear iron species of Fe/ZSM-5 at low temperatures.Figure optionsDownload full-size imageDownload high-quality image (105 K)Download as PowerPoint slide