The deactivation of a palladium on activated carbon (Pd/AC) catalyst in the hydrodechlorination (HDC) of the organochlorinated herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in water under ambient-like conditions has been studied. The loss of activity is attributed to the accumulation of organic species involved in the reaction on the catalyst surface. The analysis of the fresh and used catalysts indicated the possibility of regeneration by thermal or washing (water, NaOH solutions) treatments. Bimetallic catalysts, Pd-Rh/AC and Pd-Pt/AC, showed lower activity than the Pd/AC one but higher stability (slower deactivation). A Pd catalyst supported on an activated carbon modified upon oxidation (Pd/AC(Ox)) exhibited higher activity and stability which can be due to the high concentration of surface oxygen groups that reduced the uptake of fouling species. (C) 2015 Elsevier B.V. All rights reserved.