The performance of Fe-ZSM-5 catalysts (prepared by incipient wetness, 0.5-2.5% of Fe) for benzylation of benzene by benzyl chloride was studied in this work and explained in terms of their chemical and adsorption properties. Catalysts were characterised by ICP-MS, XPS, XRD, nitrogen physisorption and calorimetry (in order to determine their surface acidity). Adsorption properties of the catalysts (for the reactants and products) have been studied by inverse gas chromatography (IGC). Enthalpies of adsorption, dispersive energies of adsorption, and specific interaction were selected as parameters to characterise the interaction of benzene, benzyl chloride and diphenylmethane with the studied catalysts. Reaction experiments, carried out in an isothermal batch reactor, showed that increasing amounts of iron lead to more active catalyst, but less selective for the formation of diphenylmethane. Experimental data were modelled considering a serial-parallel scheme. Results reported in this paper, suggest that the reaction is controlled by the adsorption and activation of the benzyl chloride. The addition of iron to the ZSM-5 zeolite largely increases the interaction between this compound and the catalyst surface. (c) 2005 Elsevier B.V. All rights reserved.