Comparison of the Transport of Aromatic Compounds in Small and Large MFI Particles

The diffusion of alkyl-substituted aromatic molecules in two H-ZSM5 samples consisting of very small (< 100 nm) and large (similar to 3-4 mu m) primary particles was investigated by means of the frequency response method. Analysis of the experimental data in combination with the theoretical modeling of the complete transport network shows that the details of the transport processes and the rate determining step depend on the particle size. With large particles, intracrystalline diffusion was rate determining for the overall diffusion, while for the small particles the diffusion was controlled by Surface effects.