The Influence of the External Acidity of H-ZSM-5 on Its Shape Selective Properties in the Disproportionation of Ethylbenzene

The shape selectivity of H-ZSM-5 in the disproportionation ofethylbenzene was investigated, using a set of samples with thesame Si/Al ratio, but different particle sizes in the range from0.1 to 80 μm. The number of external acid sites of each samplewas measured gravimetrically by the adsorption of2,6-dimethylpyridine. The data were correlated with the resultsof catalytic experiments. Conversion and product distributionare strongly dependent on the external acidity which in turncorrelates well with the particle size. An estimate for thediffusion coefficient could be obtained by fitting theeffectiveness factor for the different particle sizes.