Ammonia oxidation and nitric oxide reduction over Cu(II)Nay zeolites

Abstract

The catalytic activity of Cu(II)NaY zeolites in the oxidation of ammonia by molecular oxygen and by nitric oxide has been investigated for a series of copper-exchanged Y zeolites. Kinetic data were determined for the reactions in a closed circulating system. Infrared spectroscopy was used to verify that copper-ammine complexes were present in the zeolite under reacting conditions. Electron paramagnetic resonance spectroscopy was used to characterize the transition metal complexes within the zeolites and to provide rate data for Cu²⁺ reduction. From these experimental investigations possible reaction mechanisms are proposed in an attempt to clarify the role of the copper-ammonia complex in oxidation reactions catalyzed by CuY zeolites. The oxidation of ammonia by molecular oxygen to nitrogen and water over CuY zeolites has been studied in the temperature range from 160 to 185°C. The reaction rate was first order in NH₃ and zero order in O₂. The rate was proportional to the degree of Cu²⁺ ion exchange up to a level of about one ion per large cavity. An activation energy of 36.7 ± 2.6 kcal/mole was observed for the three exchange levels which were studied (3%, 14%, 44%). For the 14% exchanged sample a turnover number of 0.169 (NH₃ molecules per Cu atom) min⁻¹ was observed at 175°C and an ammonia pressure of 300 Torr..