Nitrous Oxide Decomposition on the Binuclear [Fe^II(μ-O)(μ-OH)Fe^II] Center in Fe-ZSM-5 Zeolite

Abstract

The reaction mechanism for nitrous oxide (N 2 O) direct decomposition into molecular nitrogen and oxygen was studied on binuclear iron sites in Fe-ZSM-5 zeolite using the density functional theory (DFT + complex for the N 2 O decomposition. The first step of the catalytic reaction corresponds to a spontaneous adsorption of N 2 O over Fe II sites, followed by the surface atomic oxygen loading and the release of molecular nitrogen. The formation of molecular O 2 occurs through the migration of the atomic oxygen from one iron site to another one followed by the recombination of two oxygen atoms and the desorption of molecular oxygen. The computed reactivity over the binuclear iron core complex [Fe+ is consistent with experimental data reported in the literature. Although the dissociation steps of the N 2 O molecules, calculated with respect to adsorbed N 2 O intermediates, are highly energetic, the energy barrier associated with the atomic oxygen migration is the highest one. Up to 700 K, the oxygen migration step has the highest free energy barrier, suggesting that it is the rate-limiting step of the overall kinetics. This result explains the absence of O 2 formation in experimental study of N 2 O decomposition at temperatures below 623 K.

Theoretical evidence of the observed kinetic order dependence on temperature during the N2O decomposition over Fe-ZSM-5

“…Regarding kinetics and mechanism, either N 2 O dissociation or O 2 desorption have been suggested as the rate determining step in the overall process. [8][9][10][11][12][13][14][15][16][17] From DFT modeling of the…”

“…17 The decomposition of two nitrous oxide molecules into two dinitrogen and one dioxygen molecules via the following sequence steps (reactions (1)-(8)) has been examined:…”

“…However, a temperature dependence of the elementary steps has been suggested, which may explain the literature controversy on the overall process. 17 On that account, the aim of the present study is a deep investigation via kinetic experiments and modeling of elementary steps, the temperature dependence of the rate constants of the…”

“…1). 17 Overall equilibrium constants and reaction rate constants were computed using standard statistical mechanics and conventional TST. 18,19 The partition functions for reactants and transition states (TS) were calculated using the harmonic approximation.…”

N2O Decomposition over Fe‐ZSM‐5 Studied by Transient Techniques

“…ZSM-5 zeolites containing iron are known as promising catalysts in the nitrous oxide decomposition to gaseous N 2 and O 2 [1][2][3][4][5][6][7][8].…”