Direct measurements of gas diffusivity in a washcoat layer under steady state and heated conditions

• Gas diffusivity in simulated washcoat layer at heated condition was measured.
• W–K type diffusion cell was developed to measure gas diffusivity at heated condition.
• Temperature dependence of gas diffusivity was discussed.
• Mean Transport Pore Model was used.

A Wicke–Kallenbach-type counter-current diffusion cell was developed to measure gas diffusivity in a ZrO2 based simulated washcoat layer under heated conditions, by using components with high thermal resistance and designing a sample holder. Gas diffusivity was measured between room temperature and 673 K. Two pairs of gases, N2/Ar and C3H6/Ar, were used in the measurements. The temperature dependence of gas diffusivity was consistent with theory of gas diffusion. This verified validity of measurements under the heated conditions. The result of the measurement was successfully analyzed by Mean Transport Pore Model. The transport parameters from the Mean Transport Pore Model were evaluated as the geometric factor ψ of 0.19 and the mean diffuse pore radius r of 272 nm. With these parameters, the difference between actual operating conditions of monolithic catalysts and experimental conditions in this research can be bridged.