Kinetic modeling of nitrous oxide decomposition on Fe-ZSM-5 based on parameters obtained from first-principles calculations

A reaction mechanism for the decomposition of N2O on Fe-ZSM-5 has been proposed by Heyden et al. based on a detailed density functional theory analysis of the energetics for alternative pathways. This work suggested that isolated Fe cations bound to a single oxygen atom (viz., Z−[FeO]+) are the active sites for N2O decomposition. It was also shown that the presence of water vapor in the feed stream to the catalyst can deactivate these sites, but this process was demonstrated to be reversible at temperatures above about 690 K. In the present work, the decomposition of N2O was simulated under non-steady-state conditions using the mechanism of Heyden et al. and the rate coefficients calculated by these authors. These simulations closely reproduce the results of temperature-programmed reaction and pulsed N2O decomposition experiments. The dynamics of water desorption from deactivated Fe sites are found to be slow. Thus at 773 K, dehydration of a fully hydrated sample of Fe-ZSM-5 can take up to 10 h. The present study also shows that temperature-programmed desorption of O2 from Fe-ZSM-5 after N2O decomposition arises from the reaction Z−[FeO2]+ ⇄ Z−[Fe]+ + O2, but that this process is not a part of the mechanism for N2O decomposition under steady-state conditions.