Nitrous oxide decomposition and surface oxygen formation on Fe-ZSM-5

An investigation was conducted of the decomposition of N2O over Fe-ZSM-5. The zeolite used in this study was prepared with Fe and Al in the framework and is designated as Fe/Al-MFI (Si/Al=84 and Fe/Al=0.38). The as-prepared material was then calcined to remove the templating agent and pretreated at temperatures up to 1123 K. EXAFS characterization of the pretreated catalyst indicates that Fe is present as isolated Fe cations at cation-exhchange sites associated with framework Al. Above 548 K, N2O decomposes stoichiometrically to N2 and O2, but below 548 K, N2O decomposes to adsorbed oxygen and gas-phase N2. Surface oxygen loadings are in the range of O/Fetotal=0.10–0.14. For the stoichiometric decomposition of N2O to N2 and O2, the calculated values of the apparent activation energy and the preexponential factor are 44.2 kcal/mol and 9.9×108 mol N2O/(s mol Fetotal Pa N2O), respectively. The first step in the overall decomposition sequence is the dissociative adsorption of N2O to produce N2 and an adsorbed O atom. The activation energy for this step is 16.8 kcal/mol and the preexponential factor is 1.4×101 mol N2O/(s mol Fetotal Pa N2O). The desorption of O2 from iron sites occurs with an apparent activation energy of 45.7 kcal/mol and a preexponential factor of 8.9×1012 mol O2/(s mol Fetotal).