The influence of chemical and thermal aging on the catalytic activity of a monolithic diesel oxidation catalyst

Chemical and thermal aging effects and their influence on the catalytic activity were analyzed for a commercial engine aged diesel oxidation catalyst (DOC). Samples were taken from the inlet (DOCin), the middle (DOCmid) and the outlet (DOCout) area of the ceramic monolith and were compared with a new (DOCnew) and thermal aged (DOC800 °C) diesel oxidation catalyst. In all aged DOCs the platinum particles were sintered with particle diameters typically ranging between 10 and 20 nm. DOCmid, DOCout and DOC800 °C exhibited platinum particle morphology with edges and facets. Round platinum particles without discernable edges and facets were detected in the case of DOCin. DOCin showed two types of continuous, μm-thick contaminant deposits (up to 5 and 20 μm) with differing elemental compositions covering the washcoat. Catalytic activity towards the abatement of CO, propene and NO did not show any substantial difference between the different engine aged DOC samples. Thermal aging seems to be the primary cause for the observed loss in catalytic activity compared to DOCnew. However, NO2 production above 275 °C was increasing along the monolith in the order of DOCin < DOCmid < DOCout revealing a possible influence of the type of aging on activity towards NO oxidation.