A model is proposed for the average effective diffusivity for an arbitrary pore size distribution. It is shown that the average diffusivity must also depend on the distribution of the catalyst sites. The reaction diffusivity is compared with the average diffusivities defined by Wakao and Smith (1962) and Johnson and Stewart (1965). For the methanol dehydration and n-butene isomerization, the reaction diffusivity gives a better estimation of the effectiveness factor than the other models
Reaction diffusivity; porous catalyst; dehydration; isomerization
