The hydroconversion of C6-C9 n-alkanes on Pt/H-ZSM-22 was investigated by measuring and modeling of the adsorption and catalytic properties of this strongly shape-selective zeolite catalyst. Henry adsorption constants and adsorption isotherms of C6-C9 nand iso-alkanes on H-ZSM-22 were determined with chromatographic techniques and fitted to different models. While n-alkanes have access to the internal pore structure of ZSM-22, only the linear part of the iso-alkanes adsorbs in the pore entrances. Besides pore and pore mouth adsorption, external surface adsorption plays an important role. In the hydroconversion of C6-C9 n-alkanes, nonselective adsorption of n- and iso-alkanes on the external surface of the ZSM-22 crystals determines the concentration of the reacting species and the reaction orders. The skeletal rearrangement reactions occur exclusively in the pore mouths at the external surface of the zeolite crystals. The hydrocracking reactions were modeled with a lumped reaction scheme, accounting for adsorption on the different types of adsorption sites. The best,agreement between model and experiments was obtained with an external surface adsorption model. (C) 1999 Elsevier Science Ltd. All rights reserved.