Zeolite-based palladium catalysts show high activity in the reduction of NOx with methane. The addition of cobalt can further improve the SCR activity up to a level required for ‘end-of-pipe’ applications in gas engines. However, the hydro-thermal stability of the zeolite supported palladium catalysts is poor. CO-chemisorption, H2-TPR, DRIFT and activity measurements indicate a temperature-induced mechanism of ion migration and sintering to be the ruling mechanism of deactivation. In addition, the process of steam dealumination under reaction conditions likely eases the sintering. Time on stream behaviour of cobalt-palladium-zeolite equals that of palladium-zeolites. Deactivated catalysts are characterised by a palladium peak in the H2-TPR at lower temperature as compared to the fresh calcined samples. Cerium (and some other additives) stabilises the active Pd species in mordenite to a significant extent. The mechanism of stabilisation is possibly of both steric and electronic nature.
|Title of host publication||Recent Advances in the Science and Technology of Zeolites and Related Materials|
|Subtitle of host publication||Proceedings of the 14th International Zeolite Conference|
|Editors||E. van Steen, L. H. Callanan, M. Claeys|
|Number of pages||5|
|Publication status||Published - 2004|