Direct measurements of gas diffusivity in a washcoat layer under steady state conditions at ambient temperature

A method for directly measuring gas diffusivity in a washcoat layer was established by preparing a simulated washcoat layer and modifying a Wicke–Kallenbach type counter-current diffusion cell. Three pairs of gases, N2Ar, CO2Ar and C3H8Ar, were used in the measurements. It was found to be possible to evaluate the pore-transport parameters of the washcoat layer based on the mean transport pore model and the modified Stefan–Maxwell equation. Analysis of the gas diffusion mechanism in the washcoat layer showed that bulk and Knudsen diffusion took place simultaneously, and the percentage value of the contribution by Knudsen transport to net diffusion transport was evaluated.