Abstract
ZSM-5 catalysts containing either Cu or Co cations individually or Cu/Ca or Co/Ca cation combinations were prepared by ion exchange. These materials were tested as catalysts for the reduction of NO to N2 in the presence of propane or methane. Cu2+ and [Cu-O-Cu]2+ species were identified in ion exchangeable sites in the copper-containing catalysts. The amount of the latter cation increased with increasing copper content and in the presence of Ca2+ and was the most active in the reduction of NO. However, at temperatures higher than 400 ºC its activity decreased markedly. For cobalt-exchanged zeolites, Co2+ in charge-compensation sites or Co3+ in extra-framework precipitates were present in the catalysts. It was verified that the amount of Co3+ diminished with the presence of Ca2+. For the catalysts prepared in this study no significant differences in specific activity for the reduction of NO or for methane oxidation were observed in the presence of calcium.
Highlights
The improvement of catalysts used for the reduction of NO in exhaust gases is necessary in order to satisfy the increasing legal demands to reduce emission levels
As for the cobalt-exchanged zeolites the X-ray diffraction (XRD) patterns reveal the presence of fully crystalline ZSM-5 before and after ion exchange
The diffractograms further show that the samples do not contain detectable amounts of copper or cobalt oxides
Summary
The improvement of catalysts used for the reduction of NO in exhaust gases is necessary in order to satisfy the increasing legal demands to reduce emission levels. 1) observed during the preparation of |Cu0.49| and |Cu0.38Ca0.086|[Si12Al]-MFI is a further indication of the formation of such species in these catalysts.
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