N2O decomposition over Fe-ZSM-5 studied by transient techniques

Abstract

N2O decomposition to gaseous N2 and O2 catalyzed by a commercial Fe-ZSM-5 has been studied by different transient techniques: (i) via the transient response methods at ambient pressure, (ii) via the temporal analysis of products (TAP) reactor under vacuum, and (iii) by temperature-programmed desorption (TPD) under vacuum. The catalyst was activated in He at 1323 K. Two main steps can be distinguished within the transient period of N2O decomposition under constant N2O feed at 603 K: the first step consists of molecular N2 formation and surface atomic oxygen (O)Fe. It follows a period of stoichiometric N2O decomposition to gaseous N2 and O2 with increasing conversion until steady state is reached. The observed rate increase is assigned to a slow accumulation on the surface of NOx,ads species formed from N2O and participating as co-catalyst in the N2O de- composition. The NOx,ads species accelerates the atomic oxygen recombination/ desorption, which is the rate-determining step of N2O decomposition. The for- mation and accumulation of NOx,ads species during N2O interaction with the cat- alyst was confirmed by TAP studies. The amount of NOx,ads was found to depend on the number of N2O pulses injected into the TAP reactor. In the presence of adsorbed NOx on the catalyst surface (NOx,ads) the desorption of dioxygen is facilitated. This results in a shift of the oxygen desorption temperature from 744 K to considerably lower temperatures of 580 K in TPD experiments. Pulses of gaseous NO had a similar effect leading to the formation NOx,ads, thus facilitating the oxygen recombination/desorption. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.