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Values of relative interaction energy between an isobutane molecule and the surface of the H-mordenite zeolite were obtained. Sixteen tetrahedral sites were taken into account for the surface. Results showed that the adsorption energies were 4 and 8 kJ/mol, for ab initio restricted Hartree–Fock (RHF) method and density functional Becke–Lee–Yang Parr (B3-LYP) approaches, respectively, when C2&z.sbnd;H2 bond is located in front of H+ atom of H-mordenite surface. The minimum value for the interaction in the adsorption was around 2.25 and 2.50 A˚ distance from the DFT and ab initio method, respectively. The interaction of isobutane by methyl groups side over the catalytic surface caused a repulsive interaction. Therefore, adsorption of isobutane is a selective process by the H2 side of the molecule. Calculations were done by employing the 6-31G** basis set. [Copyright &y& Elsevier]