Abstract: Internal and external surface acid amount and their distribution on HZSM-5 (SiO₂/ Al₂O₃ = 38) zeolite were measured by the TPDmethod with pyridine, 2,4-dimethylquinoline and ammonia adsorption.The pore size of zeolite is characterized by the adsorption rate of cyclohex-ane.Ethylbenzene disproportionation and para-diethylbenzene isomerization were used as the test reactions for examining the shape-selectivity of catalysts.The result shows that the external surface acid is twenty percent total acid approximately.Both internal and external acids contain strong and weak acid sites.The strong acid is the active site for creaking para-diethylbenzene and ethylbenzene and it has little effect on p-isomer selectivity of disproportionation and isomerization.The m-diethylbenzene is produced mainly on the internal surface acid site, but not by isomerization of p-diethylbenzene on the external surface.The increase of para-selectivity is in a good relation to the decrease of adsorption rate of cyclohexane, but poor to the acid amount variance.Thus, the major factor which affects the selectivity of ethylbenzene disproportionation to p-isomer is the pore size of HZSM-5 zeolite, but is not the strong acid site or the isomerization of p/>-diethylbenzene on the external surface acid.

Key words: Internal and external surface acids, HZSM-5,NH₃-TPD, Ethylbenzene dispropor-tionation