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To predict how DOC performance deteriorates with a lifetime of use, it is important to understand the mechanisms of catalyst aging. In off-road applications, due to the continuous high load usage and relatively high oil consumption rate, poisoning of the Diesel Oxidation Catalyst (DOC) with Phosphorus may become an important durability issue. In this study, 3D modeling has been performed to study the P poisoning mechanism and 1D modeling has been performed to investigate P poisoning parameters that effect DOC performance deterioration. From postmortem analysis on engine aged DOCs there is a general trend that P deposits tend to collect at the outermost catalyst surface. Two types of 3D modeling were performed in this study to understand how P migrates into the bulk of the catalyst. In one case, P migrates into catalyst layer by gas phase diffusion and in the other case P first adsorbs on the catalyst surface and then migrates by solid diffusion into the bulk.

The transient HC performance of diesel oxidation catalysts is known to be greatly improved by addition of Zeolite material. The authors already reported how to estimate the effective washcoat thickness in our previous study [1]. To understand in more detail the effective catalyst layer thickness, a precise gas diffusion model and parameters of HC adsorption and desorption rate were determined in this study. The random pore model was used for a gas diffusion calculation to simulate the macro porosity of the catalyst layer and micro porosity of the Zeolite material. HC adsorption capacity as a function of temperature and HC concentration was measured by Temperature Programmed Desorption (TPD). HC desorption rate was evaluated by changing the TPD ramping rate. HC reaction rate was evaluated by using a model gas reactor. Calculated catalyst performance correlated to the experimental results, thus validating the model.