A theoretical study was carried out in order to characterize the changes produced by the presence of sulfate on the alumina surface. A molecular orbital approach of the extended Huckel (EH) type together with dynamic molecular calculation were performed to evaluate adsorption and desorption energies of the intermediate species for skeletal and double-bond isomerization reactions of n-butene The bimolecular and monomolecular mechanisms for skeletal isomerization were evaluated. (C) 2002 Elsevier Science B.V. All rights reserved.