Organic solvent free alkylation of naphthalene and t-butyl alcohol (TBA) over rare earth exchanged Y zeolite (REY) has been carried out in the presence of carbon dioxide at different process conditions (temperature between 418 and 458 K, pressure between 6 and 92 bar, TBA/naphthalene mole ratios of 1:4, and different periods of time (1.5-9 It)). The results suggest that fluid carbon dioxide can replace organic solvents as a medium for butylation of naphthalene over REY without loss of its shape selective characteristics. (C) 2002 Elsevier Science B.V. All rights reserved.