React. Kinet. Catal. Lett., Vol. 53, No. I, 79-85 (1994) RKCL2492 SPECIFIC ACTIVITY OF COPPER SPECIES IN DECOMPOSITION OF NO ON Cu-ZSM-5 Gabriele Centi, Carmelo Nigro and Siglinda Perathoner Dipartimento di Chimica Industriale e dei Materiali, V.Le Risorgimento 4, 40136 Bologna Italy Received March 16, 1994 Accepted April 19, 1994 The kinetics of NO decomposition to N 2 over Cu-ion ex- changed ZSM-5 with different Si/AI ratios and the change of the specific activity per copper site as a function of the Cu/AI ratio suggest that the copper species formed at a Cu/AI ratio of 0.5 or higher and probably containing extra-lattice oxygen have higher turnover frequency in the reaction. INTRODUCTION The direct decomposition of NO to N2+O 2 is an interesting reaction for the development of new environment-friendly cleanup technologies, because it eliminates the side pollution and the risks connected to the use of a reducing agent like ammonia. Cu-ZSM-5 shows a high activity in this reaction [I, 2], but not enough for practical applications due to the sensitivity to poisoning. Thus it is necessary to understand better the key factors governing its reactivity. However, several uncertainties exist on the nature of active species, mechanism and kinetics of this reaction. For example, kinetic data [2, 3] suggest that the rate is controlled by the desorption of oxygen, whereas in- frared data suggest the formation of a gem-dinitrosyl species as Akad4miai Kiad6, Budapest