Micro-kinetic analysis of direct N2O decomposition over steam-activated Fe-silicalite from transient experiments in the TAP reactor

Mechanistic and kinetic aspects of the direct decomposition of N2O over steam-activated Fe-silicalite were investigated by transient experiments in vacuum (N2O peak pressure of ca. 10 Pa) using the temporal analysis of products (TAP) reactor in the temperature range of 773-848 K. The transient responses of N2O, N-2, and O-2 obtained upon N2O decomposition were fitted to different micro-kinetic models. Through model discrimination it was concluded that both free iron sites and iron sites with adsorbed mono-atomic oxygen (*-O) species are active for N2O decomposition. Oxygen formation occurs via decomposition of bi-atomic (*-O-2) oxygen species adsorbed over the iron site. This bi-atomic oxygen species originates from another bi-atomic oxygen species (O-*-O), which is initially formed via interaction of N2O with iron site possessing mono-atomic oxygen species (*-O). Based on our modeling, the recombination of two mono-atomic oxygen (*-O) species or direct O-2 formation via reaction of N2O With *-O can be excluded as potential reaction pathways yielding gas-phase O-2. The simulation results predict that the overall rate of N2O decomposition is controlled by regeneration of free iron sites via a multi-step oxygen formation at least below 700 K. (c) 2006 Elsevier B.V. All rights reserved.