The conversion of a mixture of n-hexane, n-heptane, n-octane and n-nonane, in the presence of hydrogen over zeolite Pt/H-Y is modeled using a multicomponent adsorption-reaction scheme. Adsorption parameters for the relevant hydrocarbon molecules are determined using the chromatographic technique. Intrinsic reaction parameters are obtained by the fitting of the model to reaction rate data from catalytic experiments, using the independently determined adsorption parameters. Preferential conversion of the longer n-alkanes in mixtures is caused by competitive adsorption favoring the heavy compounds. Apparent reaction rates in mixtures are controlled by adsorption, increasing with chain length of the n-alkanes, rather than by the individual intrinsic reaction rates of the different n-alkanes, which are similar.