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Transport limitations inside the porous washcoat layer have an important influence in the light-off and overall conversions even in the case of relatively thin layers used in automotive three way catalysts (TWC). The porous structure of the washcoat layer is controlled at two levels: i) at the level of mesoporous structure, which can be determined by the use of specific synthesis techniques (e.g., sol-gel or pore-templating method), and ii) at the level of macroporous structure, which is influenced by the particle size distribution of mesoporous in a slurry that has undergone a specific thermal treatment. This paper investigates the influence of the washcoat structure in the performance of automotive TWC. Furthermore, the article presents a method that allows to quantify the magnitude of the reaction resistance (chemical kinetics), internal mass transfer resistance (washcoat diffusion), and external mass transfer resistance on the TWC conversions.