n-Dodecane was hydroisomerized over Pt supported on Y zeolites with different acid characteristics in a batch reactor. The Y zeolites used were NaY, HY (SiO2/Al2O3= 5.1), HY (SiO2/Al2O3 = 80), and HY (SiO2/Al2O3= 200). NaY was ion exchanged with NH4Cl to impart acidity. HY (SiO2/Al2O3 = 5.1) and HY (SiO2/Al2O3 = 80) were silylated to modify their acidity. HY(80) and NaY(5.1) zeolites were examined by XRD and NMR methods only, while Pt/Nay and Pt/HY samples were subjected to investigation, besides XRD method, by N-2 adsorption/desorption, NH3 TPD, and FT-IR methods. For NaY, HY (SiO2/Al2O3= 5.1), HY (SiO2/Al2O3= 80) and HY (SiO2/Al2O3= 200), the conversion of n-dodecane decreased with increasing SiO2/Al2O3, whereas selectivity of isomerization increased with increasing SiO2/Al2O3. HY (SiO2/Al2O3 = 80) showed the best hydroisomerization activity. The catalytic activities of NaY and HY (SiO2/Al2O3= 5.1) were enhanced significantly by ion-exchange and silyation, respectively. The effects of temperature, pressure and Pt loading on the catalytic activity were also investigated. (C) 2013 Elsevier B.V. All rights reserved.