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ECN publication
Durability of ZSM5 supported Co-Pd catalysts in the reduction of NOx with methane
Published by: Publication date:
ECN 1-12-2002
ECN report number: Document type:
ECN-RX--02-063 Article (scientific)
Number of pages:

Published in: Accepted for publication in 'Applied Catalysis B, 2002' (), , , Vol., p.-.

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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