The hydrogenation of tetralin in the vapor phase has been investigated over Ni, Pt, and Pd catalysts to determine the evolution of the trans-and cis-decalin products as a function of conversion over the different catalysts. The concentration of each isomer in the product may be important in subsequent ring opening steps if cetane number improvement is desired. The cis-decalin isomer is preferred to open the naphthenic ring in a selective way instead of multiple cracking. However, thermodynamically, this isomer is the least favored; so, kinetic control is the only solution. By selecting the proper catalyst and operating conditions, one could keep the trans/cis-decalin ratio low. In this study, we have prepared a series of supported metal catalysts and tested them in a flow reactor at 3540 kPa and 548 K. Kinetic parameters for the hydrogenation of tetralin and the cis-to-trans-decalin isomerization over the various catalysts investigated were obtained by fitting the data with a generalized Langmuir-Mnshelwood model. The kinetic analysis revealed that the relative rates of tetralin hydrogenation, as well as the cis-to-trans isomerization are greatly affected by adsorption site competition of decalin and tetralin, which in turn has different magnitudes over the different catalysts. At tetralin conversions above 30%, the Ni catalyst yields the lowest trans/cis-decalin ratio. In contrast, the trans/cis ratio on Pd catalyst remains constant at all conversion levels and is highest at low tetralin conversion. It is concluded that the trans/cis ratio is a combination of the intrinsic selectivity of each isomer and the isomerization reaction. (c) 2007 Elsevier B.V. All rights reserved.