Catalytic Decomposition of Nitrous Oxide over Cu Catalysts -Effects of Carriers.-

Abstract

The decomposition of N₂O was carried out with several copper catalysts such as copper ion-exchanged ZSM-5, mordenite, and Y-zeolite, cupric oxide supported on y-alumina, and perovskite-related La_1.5Sr_0.5CuO₄. The amounts of copper exposed on the surface were estimated by NO adsorption at 273 K and N₂O oxidation at 363 K. It was found that more than 80% of t otal copper ions w ere expose d on t he surface for ZSM-5, 50--60% for mordenite, and less than 20% for Y zeolite and y-alumi na. The catalytic activities, expressed by the rate of N₂O decomposition per surface copper (Turnover Frequ ency, TOF), increased greatly with an increase in the copper content for ZSM-5, while it increased only slightly for mordenite, Y zeolite and y-alumina. The TOF of ZSM-5 was a bout 100 t imes greater t han those of mordenite, Y zeolite and y-alumina when compared at the copper weight content of 5 %. L a_1.5Sr_0.5Cu₄, which had a very small specific surface area due to high-temperature calcination, sho wed much greater TOF than mordenite, Y zeolite and y-alumina, but lower than ZSM-5. The exam ination of the diffusion constraints within the zeolite pore system revealed that catalytic effective ness factors were approximately unity, so t hat the dinsion of N₂O in micro and meso pores did not affect the reaction rate and TOF observed in this work would reflect the intrinsic catalytic activity.