The decomposition of a mixture of (N2O)-N-15 and (N2O)-N-14 does not lead to a formation of (NN)-N-14-N-15 on Fe-ferrierite, so that the N-N bond is not dissociated during this reaction. On the other hand, mono-nitro NOx surface species are created during the N2O decomposition, and are desorbed as NO2 and NO into the gas phase above 300 degrees C. The reaction of N2O with active oxygen is suggested to explain their formation. NO2 and NO are also found after the addition of NO to N2O which substantially enhances the nitrous oxide decomposition. The addition of CO instead of NO accelerates the N2O decomposition and suppresses the formation of surface NOx species. The dependence of the decomposition of nitrous oxide on the added CO and/or NO is different. Operation of both agents is discussed together with the temperature of the Fe-ferrierite pretreatment.