Direct evidence for the formation of surface Fe-NOx species over iron ferrierites during decomposition of N2O was found with a combination of temperature-programmed desorption of adsorbed surface species and infrared and Mossbauer spectroscopies. Surface NOx species were produced via the conversion of a transiently formed Fe(III)-O by exposing iron ferrierites (Si/Al = 8.7, Fe/Al = 0.07-0.1) to N2O. The transformation of Fe(III)-O into Fe-NOx was time- and temperature- dependent. Below 280 C, predominantly Fe(III)-O species were formed; these species are known to be highly active in oxidations at low temperatures. A transformation of Fe(III)-O into Fe-NOx species occurred when the reaction temperature was increased or when the reaction time was increased at low temperatures. This resulted in the disappearance of the oxidation activity of iron ferrierite. In contrast, the formation of Fe-NOx species enhanced the rate of N2O decomposition. Once formed, NOx species were stable during the subsequent N2O decomposition. (C) 2012 Elsevier Inc. All rights reserved.