Hydroisomerization of a mixture Of C-5-C-7 n-paraffins and simultaneous saturation of benzene was studied over bifunctional Pt/H-ZSM-12 catalysts, with a sulfur free feed and with the feed containing 200 ppm of thiophene. The performance of a Pt/H-ZSM- 12 catalyst was also compared with a Pt/H-beta and a Pt/H-mordenite catalyst having a similar Si/Al ratio. The three Pt/H-ZSM-12 catalysts, having different Si/Al ratios, showed very similar activity and selectivity characteristics. Presence of benzene in the feed had no effect on the isomerization over the Pt/H-ZSM-12 catalysts. Compared to the Pt/H-beta catalyst, Pt/H-ZSM-12 and Pt/H-mordenite required higher temperatures to achieve the same conversion level. The lower activitv of Pt/H-ZSM-12 and Pt/H-mordenite is in agreement with the behavior expected from a one-dimensional structure. However, at comparable conversion levels, cracking reactions, especially that of heptane, occurred to a lesser extent over the Pt/H-ZSM- 12 catalyst resulting in a significantly higher yield of the branched paraffins than over Pt/H-beta or Pt/H-mordenite. In the presence of 200 ppm of thiophene, both the isomerization and the benzene hydrogenation activity of the Pt/H-ZSM- 12 and Pt/H-mordenite catalysts decreased but the Pt/H-beta catalyst was affected only to a small extent. Moreover, in the presence of sulfur, cracking occurred to a greater extent at the same conversion level over all the catalysts. The estimated research octane number (RON) of the C5+ products varied in the same manner with respect to the conversion over all the catalysts, but a higher yield of these products is obtained over Pt/H-ZSM-12 in the absence of sulfur. Although Pt/H-beta is much more active and has better sulfur resistance, the capability of Pt/H-ZSM- 12 to provide a significantly higher yield of isomers makes it an attractive catalyst. (C) 2003 Elsevier Science B.V. All rights reserved.