Catalytic decomposition of nitrous oxide over Cu catalysts - Effects of carriers

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 gamma-alumina, and perovskite-related La1.5Sr0.5CuO4. 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 total copper ions were exposed on the surface for ZSM-5, 50-60% for mordenite, and less than 20% for Y zeolite and gamma-alumina. The catalytic activities, expressed by the rate of N2O decomposition per surface copper (Turnover Frequency, TOF), increased greatly with an increase in the copper content for ZSM-5, while it increased only slightly for mordenite, Y zeolite and gamma-alumina. The TOF of ZSM-5 was about 100 times greater than those of mordenite, Y zeolite and gamma-alumina when compared at the copper weight content of 5%. La-1.5 Sr0.5CuO4, which had a very small specific surface area due to high-temperature calcination, showed much greater TOF than mordenite, Y zeolite and gamma-alumina, but lower than ZSM-5. The examination of the diffusion constraints within the zeolite pore system revealed that catalytic effectiveness factors were approximately unity, so that the diffusion 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.