Comparison of light-off performance of Pt-Pd/γ-Al2O3 dual layer and dual brick diesel oxidation catalysts

A global kinetic model is used to study the light-off behavior of a mixture of CO and HCs (C2H4,C7H8,C6H14 & C2H6) on Pt, Pd and combined catalysts. The light-off curves are clustered around 550 K on Pt whereas species light-off temperatures range from 400-600 K on Pd. The self poisoning of CO is more pronounced on Pt than on Pd. As long chain HCs such as hexane have a better light-off performance on Pt than on Pd, it is beneficial to use dual layer or dual brick catalysts for optimising HC conversion on a C1 basis. Dual brick catalyst with Pd upstream showed superior performance compared to the configuration with Pd downstream. Pt in 50% of washcoat and Pd in the remaining 50% of washcoat has a better overall light-off performance than other fractions of Pt, Pd. It is found that the light-off behavior of all the species is nearly same for both dual layer and dual brick configurations at low space velocities. However, the strong diffusional limitations in the washcoat at high space velocities result in improved light-off performance of dual layer configuration. The more practical C1 basis conversion, which is the weighted average conversion of HCs, is investigated for different configurations. It is also shown that the exotherm generated by the oxidation of CO can be used to improve the C1 basis conversion of HCs.