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Title:
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Durability of ZSM5-supported Co-Pd catalysts in the reduction of NOx with 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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1-4-2002
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ECN report number:
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Document type:
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ECN-RX--02-058
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Article (scientific)
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Number of pages:
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13
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Published in: Applied Catalysis B: Environmental 39(2002) p. 167-179. ISSN 0926-3373 (Elsevier), , , Vol., p.-.
Abstract:
Selective catalytic reduction (SCR) of NO with CH4 was studiedover ZSM5-based cobalt and palladium catalysts in the presence of oxygen
and water. Pore volume impregnation of cobalt was found to be more efficient
and much simpler than the common (wet) ion-exchange method. In the case
of Pd, wet ion-exchange was found to give superior activity. As compared
to alternative catalytic systems reported in literature for CH4-SCR
in the presence of water, ZSM5-supported Co-Pd combination catalysts
are very active and selective. The activity of the ZSM5-based Co-Pd
combination catalysts, however, decreases strongly with time-on-stream.
Strikingly, this deactivation is not (predominantly) caused by steam
dealumination of the zeolites: loss of SCR activity with time-on-stream
occurs irrespective of the presence or absence of water in the feed.
The higher the temperature of calcination the lower the initital activity
and the faster the deactivation. In addition to this, the deactivation
is also more pronounced at higher reaction temperatures. These observations
are consistent with a temperature-induced mechanism of ion migration
and sintering as also confirmed by TPR analysis. The role of water in
this migration process is not obvious. Hence, the limited thermal stability
of ZSM5-supprted metal (ion) catalysts lead to two demands, which have
yet to be made for application of zeolites in CH4-SCR: (1)
stabilisation of the ionic phases in zeolite pores of different geometry;
and (2) further improved activity and selectivity allowing one to operate
at temperatures that do not exceed 350-400 degrees C, where deactivation
is not significant.
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