Modelling of the behaviour of a three way catalytic converter at steady state - Influence of the propene diffusion inside the catalytic layer

A steady-state film model, accounting for the species diffusion inside the catalytic layer, was developed. This model demonstrates that diffusional li mitations within the washcoat limit the propene conversion. The effectivene ss factor was found lower than 1 at any location along a channel of the cat alytic converter, for inlet temperatures higher than 500 K. These diffusion al limitations within the washcoat had to be accounted for to extract the k inetic rate of propene oxidation in agreement with the experimental measure ments of the extent of propene conversion at different temperatures. The ef fectiveness factor is not affected by a transient state since the character istic time scale for internal diffusion is much less than the period of flu ctuation of the gas composition. The effective diffusivities of propene and oxygen are key parameters for the efficiency of the propene conversion. Th e platinum content is less determining since the concentrations of propene and oxygen significantly decrease along the thickness of the washcoat. A st udy of the external mass transfer, affected by the hydraulic diameter, show ed that a decrease in the channel diameter significantly increases the exte nt of propene conversion for temperatures higher than 500 K. (C) 2000 Publi shed by Elsevier Science Ltd. All rights reserved.