ZSM-5 Pore Size

ZSM-5 has the MFI framework topology with a medium-pore channel system built from 10-membered rings.

Channel Dimensions

ZSM-5 contains two intersecting channel types:

The intersection of these channels creates a slightly larger cavity where shape-selective catalysis occurs. The effective pore size (~5.5 A) excludes molecules with kinetic diameters above approximately 6 A.

What Fits, What Doesn’t

Shape Selectivity Mechanisms

1. Reactant selectivity: Molecules too large to diffuse through the 10-MR channels cannot reach internal acid sites
2. Product selectivity: Among product molecules formed inside the pores, only those small enough to diffuse out are recovered — bulkier isomers are retained and may undergo further conversion
3. Restricted transition-state selectivity: Bulky reaction intermediates that cannot form within the constrained pore intersections are suppressed, favouring pathways that proceed through linear or slightly branched intermediates

This combined shape selectivity is what makes ZSM-5 indispensable for applications like FCC additives (preserving high-octane branched components), MTO (favouring linear olefins), and para-selective alkylation.

For detailed specifications, see the ZSM-5 specifications page. Request a sample with your target application.