The interaction of C-4-hydrocarbons with the surface of two sulfated zirconias of considerable different catalytic activity has been investigated by using the temporal analysis of products (TAP) reactor. n-Butane and iso-butane as reactant and product molecules for the isomerization showed differences in their interaction with the surface of sulfated zirconia thus indicating slightly variable sorption features for both molecules. 1-Butene, as representative for a possible reaction intermediate or side product, had compared to the saturated C-4-molecules stronger adsorption abilities and desorbed slower from the surface of sulfated zirconia, which may also influence the sorption properties of n-butane and iso-butane during the catalytic cycle. Heats of adsorption from van't Hoff plots were modelled for n-butane and isobutane and are comparable to calorimetry data for this system thus giving the opportunity to model the first step in a microkinetic model appropriately. (C) 2004 Elsevier B.V. All rights reserved.