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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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1-12-2002
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ECN report number:
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Document type:
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ECN-RX--02-063
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Article (scientific)
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Number of pages:
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28
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Published in: Accepted for publication in 'Applied Catalysis B, 2002' (), , , Vol., p.-.
Abstract:
Selective catalytic reduction of NO with CH4 was studied over ZSM5-basedcobalt (Co) and palladium (Pd) 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 CH-4-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 initial 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 supported metal (ion) catalysts leads 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°C, where deactivation is not significant.
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