The tightening emission regulations have led to the development of commercial DOCs with zoned or layered formulations allowing to cover a wide range of functionalities (i.e. CO, HC and NO oxidation as well as HC or NOx trap). Aging phenomena in such complex formulations are not well understood. To shed light on material deactivation, this study compares phosphorus poisoning and thermal sintering of two DOC monoliths with related formulations: (1) a commercial monolith comprising two catalytic layers where the top layer is rich in Pt, and (2) a model monolith containing only the top layer of the commercial monolith. The activity and characterisation (elemental analysis, microscopy and N₂-physisorption) results are used to deconvolute the deactivation process of the two layers and should serve to rationalize the aging in layered catalyst formulations.