Journal
TOPICS IN CATALYSIS
Volume 56, Issue 1-8, Pages 493-498Publisher
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s11244-013-0004-7
Keywords
Exhaust gas cleaning; NOx selective reduction; Soot oxidation; Alkali promoters; Washcoating; Structured catalysts
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Structured catalysts prepared by means of coating cordierite monoliths with alumina-based suspensions containing transition metals such as Cu, Co and Fe and alkali/alkali-earth promoters such as K and Ba. Textural and structural features of these catalysts were analyzed by means of N-2 adsorption and SEM. Their activity in the simultaneous removal of soot and NOx was assayed in a lab-scale installation, using a carbon black as diesel surrogate. Catalysts exhibited significant activity in deNO(x) and soot oxidation. K and Ba enhanced both NOx adsorption and soot-catalyst contact. However Ba contributed to a greater extent to the adsorption of N-species, which moreover presented higher thermal stability than on K-catalysts, and K showed higher mobility than Ba. Thus, Ba-containing catalysts showed increased activity towards NOx reduction but shifted to higher temperatures in comparison to K-catalysts, which on the other hand resulted more active towards soot oxidation than Ba-ones. Fe-based catalyst turned out to be less active both in soot oxidation and NOx reduction than Co and Cu-based ones. Intensive calcination of the catalysts at 800 A degrees C for 5 h resulted in substantial loss of K and Ba. Loss of promoter depends, however, on the metal contained in the catalyst. In this sense Fe-containing catalysts showed higher stability. Calcination has a substantial effect on catalytic activity. Catalyst significantly lost their NOx adsorption capacity and showed similar activity than a catalyst prepared in absence of promoter, pointing to a substantial change in reaction mechanism and reaction predominantly occurring on metallic sites upon the loss of alkali/alkali-earth compound.
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