The deactivation of a 0.5 wt.% Pd on alumina catalyst used for the hydrodechlorination of tetrachloroethylene (TTCE), chlorobenzene (CBZ) and dichloromethane (DCM) in organic matrix in gas phase has been studied in this work. Experiments were carried out in a continuous fixed bed reactor, at a pressure range of 0.1-2 MPa. It was found that the reactivity and stability of the catalyst increases as pressure increases. Different compounds present quite different deactivation patterns: fast initial deactivation followed by a plateau for DCM and CBZ, continuous moderate deactivation for TTCE. The effect of hydrogen chloride was studied by adding to the reactor feed different amounts of hydrogen chloride, working at 225-300 degrees C. Fresh and used catalysts were characterised by nitrogen porosimetry, X-ray diffraction, transmission electronic microscopy, scanning electronic microscopy, thermogravimetry and temperature-programmed oxidation. Results indicate that carbonaceous deposits play a key role in the catalyst deactivation, being this phenomenon promoted by the presence of HCl. (c) 2005 Elsevier B.V. All rights reserved.