Effects of pore diffusion on Rate of heterogeneous chemical reaction
The Weisz–Prater criterion is a method used to estimate the influence of pore diffusion on reaction rates in heterogeneous catalytic reactions. If the criterion is satisfied, pore diffusion limitations are negligible. The criterion is 
formula_1
Where formula_2 is the reaction rate per volume of catalyst, formula_3 is the catalyst particle radius, formula_4 is the reactant concentration at the particle surface, and formula_5 is the effective diffusivity. Diffusion is usually in the Knudsen regime when average pore radius is less than 100 nm.
For a given effectiveness factor,formula_6, and reaction order, n, the quantity formula_7 is defined by the equation:
formula_8
for small values of beta this can be approximated using the binomial theorem:
formula_9
Assuming formula_10 with a reaction order formula_11 gives value of formula_7 equal to 0.1. Therefore, for many conditions, if formula_13 then pore diffusion limitations can be excluded.