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Titel:
Stability of zeolite supported (promoted-) Pd catalysts in the reduction of NOx in gas engines using methane
 
Auteur(s):
 
Gepubliceerd door: Publicatie datum:
ECN SF 1-12-2003
 
ECN publicatienummer: Publicatie type:
ECN-RX--03-068 Overig
 
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Samenvatting:
Zeolite-based palladium catalysts show high activity in the reductionof 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.


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