Zoning and Trapping Effects on CO and Hydrocarbon Light-Off in Diesel Oxidation Catalysts
2017
Kang, Sung Bong | Kalamaras, Christos | Balakotaiah, Vemuri | Epling, William
Monometallic Pt and bimetallic Pt/Pd oxidation catalysts, as model diesel oxidation catalysts, were tested in the oxidation of CO, C₂H₄, C₂H₆, C₇H₈, and C₆H₁₄. These single monolith catalysts were then compared to a dual-zoned system, where two monoliths were placed in series and the zones were comprised of different Pt/Pd ratios. Finally, a dual-layered system was also evaluated, where the added layer was made of Ag/BEA as a hydrocarbon trap. In terms of trends observed, for the single-zoned system, increasing the Pd content led to increased CO oxidation activity, while the best hydrocarbon oxidation was observed with increasing Pt content, except in the case of C₂H₆. An improvement in overall oxidation performance was achieved with the dual-zoned system, where a catalyst with a 1:5 Pt:Pd ratio upstream and monometallic Pt downstream proved best of those tested. This is attributed to a combination of relatively high CO oxidation in the upstream high-Pd content piece and the relatively high hydrocarbon oxidation with decreased CO inhibition in the high-Pt content downstream piece. Moreover, the addition of Ag-BEA as a top layer of the dual-zoned oxidation catalyst did result in hydrocarbon trapping, particularly toluene, in the low-temperature region. These results provide useful insight into system-level designs that might be applied to improve low-temperature oxidation performance especially.
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