To clarify the mechanism of naphthalene hydrogenation to cis- and trans-decahydronaphthalene (decalins) via tetrahydronaphthalene (tetralin), the rate of naphthalene hydrogenation was compared with those of tetralin and tetralin containing 3-10 mol% naphthalene over a TiO2-supported Pt catalyst. Tetralin was hydrogenated to decalins readily, while the naphthalene hydrogenation did not take place under the same reaction conditions (433 K and 2.96 MPa). When 3-10 mol% naphthalene was added to tetralin, the rate of hydrogenation decreased clearly with an increase of naphthalene content. The observation suggests that naphthalene interacts with surface metals strongly and prevents the hydrogenation of tetralin. (C) 2002 Elsevier Science B.V All rights reserved.