Nitric oxide reduction with ammonia to nitrogen, nitrous oxide, and water over CuY zeolites has been studied in the temperature range from 80 to 150 °C. An unusual catalytic activity-temperature profile was observed with a maximum rate observed at 110 °C, similar to that recently reported by Seiyama et al. The reaction rate was first order in NO and zero order in NH3. The rate was proportional to the degree of Cu2+ ion exchange. For a 6.5% CuY sample a turnover number of 0.13 NO molecules per minute per Cu2+ ion was observed at 108 °C and a NO pressure of 50 Torr. The reduction of NO with 15NHs indicated that the product 14N15N derived one nitrogen atom from each of the reactants; whereas, the product 14N20 was derived from NO. A kinetic isotope effect of ^nh3/^nd3 -1.5 was observed at 112 °C when substituting ND3 for NH3, butwas not observed at 130 °C. The slow step in the reaction mechanism at temperatures less than 110 °C involves the reaction of coordinated ammonia with nitric oxide. Above 110 °C the reduction of the blue Cu(II) complex to a white Cu(I) complex becomes significant as confirmed by electron paramagnetic resonance. At the higher temperatures the reaction mechanism includes an oxidation-reduction step in which the oxidation of the Cu(I) complex is much slower than the reduction of Cu(II). Infrared and EPR evidence is interpreted in terms of a reactive [Cu(NHa)4]2+ complex which is bound to the zeolite through a bridging nitro group.

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