Catalytic hydrodechlorination has been intensely studied recently since it seems to be a promising method for treating toxic organochlorine residues. In this context, the aim of this work is to study the reaction conditions for pentachlorophenol hydrodechlorination, conducted in a three-phase media with palladium catalysts. The study was carried on a commercial Pd/C catalyst and a Pd/TiO2 catalyst, which was prepared by the dry impregnation technique from the PdCl2 precursor. Preliminary catalytic tests indicated that for both catalysts, previous reduction significantly reduced their catalytic activities, while calcination at 573 K leads to active catalysts in the reaction. Owing to the undesirable retention of pentachlorophenol observed using the Pd/C catalyst, the Pd/TiO2 system was used to study reaction conditions by means of a 2(6-2) fractional factorial design. One combination of levels of this design permitted establishing suitable reaction conditions for this hydrodechlorination. (c) 2007 Elsevier B.V. All rights reserved.