Activation of ammonia dissociation by oxygen on platinum sponge studied with positron emission profiling

摘要

Positrom emission profiling (PEP) is applied to study the adsorption and dissociation of ammonia on metallic and preoxidized platinum spong in the temperature range 323-537 k The results show that ammonia weakly interacts with platinum without dissoiation On the contrary preoxidized platinum is able to dissociate ammonia With increasing temperature more ammonia is converted into N_2 N_2O and H_2O Adsorbed NO appears to be an important interamediate while its formation stronglyi depends on the oxygen surface coverage Temperatureprogrammed experiments are performed to characterize the adsorbed nitrogen species Furthermore H_2 NH_3 and NO are used to react with these adsorbed nitrogen species These experiments indicate that mainly NH_x species are present at the platinum surface.