The aqueous-phase batch hydrodechlorination (HDC) of 2,4-dichlorophenol (2,4-DCP), over 1 wt/wt% Pd/Al 2O 3 and Pd/C has been investigated with/without the addition of NaOH, NH 4OH, LiOH, KOH, RbOH, and CsOH; bulk solution pH spanned the range 1.5–13. The reaction was operated in the kinetic-controlled regime with 2-chlorophenol (2-CP) as the only intermediate partially dechlorinated product which reacts further to yield phenol; cyclohexanone was formed over Pd/Al 2O 3, but not Pd/C, prior to the completion of dechlorination. An increase in fractional dechlorination with the addition of base was observed and can be attributed to a suppression of HDC inhibition due to the HCl that is generated. The initial HDC activity and selectivity delivered by both catalysts were pH dependent and differences in response to bulk solution pH variations are discussed in terms of the nature of the reactive species in solution and the amphoteric behavior of the Pd supports. The Pd/Al 2O 3 catalyst is characterized by a high surface charge density while Pd/C bore a low basic functionality density on a high surface area carrier. A maximum initial HDC rate over Pd/Al 2O 3 was attained at pH 7–9 while a higher pH (⩾9) results in more effective HDC for Pd/C, effects that are linked to chloroarene dissociation and surface charge effects. In the case of Pd/C, the initial HDC rate with the addition of alkali metal hydroxide ( 0.074 mol dm −3 ) increased in the order Li +≈Na +<K +≈Rb +<Cs +, a sequence that matches the adsorption affinity on a negatively charged carbon surface; HDC over Pd/Al 2O 3 was insensitive to the nature of the alkali metal cation. The action of NH 4OH, as a weak base, is also considered.