Catalytic decomposition of nitric oxide over copper(II)-exchanged, Y-type zeolites

Abstract

The catalytic decomposition of NO has been investigated over copper(II)-exchanged Y-type zeolites (CuNaY) at 573–823 K in a flow reactor. CuNaY exhibited an appreciable activity above 723 K and was not poisoned by either oxygen or water vapour. In the presence of the CuNaY catalyst (69% exchanged) using a contact time of 11 g(catalyst) s cm^–3(gas), the extent of elimination of NO (4 vol%) in diluent helium was found to attain ca. 100% at 773 K. Below 673 K, the catalytic activity slowly declined with increasing reaction time and was restored to its original state upon heating the catalyst above 723 K. This phenomenon results from the accumulation and desorption of oxygen released from the decomposed NO. The influence of the Cu^II ion-exchange level on the catalytic activity has been examined and it was concluded that the active sites for the reaction are the Cu^II ions located at sites S_II and S_III. Upon adsorption of NO at 273 K on CuNaY substantial amounts of N₂O, N₂ and O₂, as well as NO, appear in the temperature-programmed desorption chromatogram. Based on the results of thermal desorption of various adsorbates and the temperature-dependence of N₂O decomposition, two reaction paths of NO are proposed, including direct decomposition to N₂ and O₂ and consecutive decomposition through N₂O as an intermediate.