Investigation of the deactivation of a washcoated monolith using a spatially resolved technique

Abstract

A spatially resolved technique was used to investigate the impact of deactivation on the spatial distribution of the effective diffusion in an aged washcoated monolith catalyst. The technique was applied to the investigation of the reactants and products of CO oxidation inside a commercial Pd/Al₂O₃ monolith catalyst. The spatially distributed effective diffusivities of O₂, CO and CO₂ were resolved and calculated by a modified Bosanquet approach, which confirmed that the dominant diffusion regimes in the substrate and the washcoat were molecular and Knudsen respectively in the zone affected by deactivation. The technique illustrated the extent to which the deactivation, and its impact on diffusion, varied throughout the washcoat. The results presented are of relevance to the simulation of aged catalysts for automotive applications. In scenarios such as this it is common to model the reduction in catalyst activity by reducing the surface area of the precious metal, with the washcoat diffusion parameters set to their initial, non-aged values. This research quantifies the significant extent to which the diffusion parameters are affected which, when incorporated into catalyst models, will result in more accurate predictions of vehicle emissions.