The dialkylation of naphthalene with isopropanol to produce 2,6-diisopropylnaphthalene (2,6-DIPN) was carried out over HY zeolite. The effects of various reaction conditions, such as pressure, temperature, space velocity, molar ratio of alcohol to naphthalene and time on stream (TOS) on product distribution were studied. HY zeolite was modified by transition metals, such as Fe3+, Ni2+, Co2+ and Cu2+ using wet impregnation method to maximize the selectivity to 2,6-DIPN. The catalysts were characterized by XRF, XRD, TGA, nitrogen adsorption-desorption and Temperature Programmed Desorption (TPD) of t-Butylamine. Under optimum reaction conditions, (50 bar, 220 degrees C, isopropanol/naphthalene = 4 (mole ratio), WHSV = 18.8 h(-1), TOS 6 h), HY zeolite modified by Fe3+ was found to give the highest selectivity, by increasing the 2,6/2,7-DIPN ratio from 2.8 to 6.6. The experimental results indicate that the selectivity to 2,6-DIPN is in the order of Fe-HY > Ni-HY > Cu-HY > Co-HY > HY. Naphthalene conversion of 77% was obtained over HY zeolite, while after modification by Fe, Co, Ni and Cu, the conversion was changed to 73%, 76%, 88% and 96%, respectively. TPD result indicates different distribution of weak, medium and strong acid sites in the modified catalysts. TGA analysis of used catalyst samples revealed that a higher amount of PIPN was produced on zeolite modified by Co and Cu. This confirms that PIPN molecules are possible coke precursors, and therefore led to larger amount of coking on the Co-HY and Cu-HY catalysts. (C) 2012 Elsevier B.V. All rights reserved.