Applying the Horvath-Kawazoe approach for: the slit, cylindrical and spherical pore models for the description of the geometry of the channels and cavities of nanoporous materials, and the united-atom model to describe n-alkanes of, m, carbons; were calculated mathematical expressions to describe the enthalpy of adsorption of these alkanes in acid nanoporous materials, such as zeolites and mesoporous molecular sieves. After that, applying ideas developed by Haag, Gorte and others, and the transition state theory, the expressions for the enthalpy of adsorption were linked with the observed and intrinsic activation energies for the unimolecular catalytic cracking reaction. To evaluate the implicit mathematical expressions for the enthalpy of adsorption were used parameters which characterize methane and the adsorbent surface, and was carried out a detailed experimental analysis of the pore diameters of the tested materials. The obtained numerical equations were plotted and tested with reliable literature data, obtaining results which fairly well coincide with the reported experimental values. (c) 2007 Elsevier B.V. All rights reserved.