Limited penetration depth occurs due to several factors:
Surface Area: The catalytic reactions primarily happen on the surface or near-surface regions of the catalyst. Larger surface areas mean more active sites for the reactions, but this doesn't necessarily translate to deeper penetration. Diffusion Limitations: The reactants may not be able to diffuse deeply into the catalyst material. This can be due to physical barriers or because the reactants are consumed rapidly at the surface. Active Site Distribution: Often, the active sites are concentrated near the surface, leading to more activity in these regions and less in deeper layers.
