There are primarily two types of diffusion relevant to catalysis:
Molecular Diffusion: Occurs when molecules move due to concentration gradients. It's significant in homogeneous catalysis where the reactants and catalyst are in the same phase. Knudsen Diffusion: Dominates when the mean free path of the diffusing molecules is comparable to the pore size of the catalyst. This is particularly important in porous catalysts with very small pores.
