Zoning and Trapping Effects on CO and Hydrocarbon Light-Off in Diesel Oxidation Catalysts

Abstract

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 ox...