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Title:
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Stability of zeolite supported (promoted-) Pd catalysts in the reduction of NOx in gas engines using methane
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Author(s):
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Published by:
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Publication date:
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ECN
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1-12-2003
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ECN report number:
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Document type:
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ECN-RX--03-068
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Other
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Number of pages:
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Full text:
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8
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Download PDF
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Abstract:
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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