Hydrogenation of naphthalene over Pd/TiO2 and Pd/Al2O3 catalysts in the presence of dimethyldisulfide (DMDS) was performed in a batch reactor at 473 K and 2.45 MPa; the two catalysts were compared in detail in terms of sulfur tolerance. As compared with Pd/Al2O3, Pd/TiO2 showed high turnover frequency (TOF) and sulfur tolerance, in both the presence of dimethyldisulfide (DMDS) and the absence of DMDS. Pd-S bond strength was determined by temperature-programmed reduction of sulfide catalysts (H2S-TPR) profiles and CO uptake after H-2 reduction of sulfided catalyst at various temperatures. The results show that desorption of H2S from sulfided Pd/TiO2 occurs at 553 K, whereas desorption of H2S from sulfided Pd/Al2O3 requires a higher temperature (773 K), indicating that the Pd-S bond in Pd/TiO2 is significantly weaker than that in Pd/Al2O3. Furthermore, the H2S-TPR profiles of Pd/TiO2 reduced at 573-773 K clearly indicate that the Pd-S bond in Pd/TiO2 reduced at 573 K is weak, whereas reduction at high temperature (SMSI state) strengthened the Pd-S bond. The high temperature reduction may result in formation of Ti3+ surrounding the Pd metals and spoil the catalytic activity. Therefore, the presence of Ti4+, which has a high electronegativity, is concluded to weaken the Pd-S bond and to be an important factor for high sulfur tolerance. (C) 2003 Elsevier Science B.V. All rights reserved.