Catalytic hydrodechlorination (HDC) is an effective means of detoxifying chlorinated waste. Involvement of spillover hydrogen is examined in gas phase dechlorination of chlorobenzene (CB) and 1,3-dichlorobenzene (1,3-DCB) over Pd and Ni. The catalytic action of single component Pd and Ni, Pd/Al2O3, Ni/Al2O3 and physical mixtures with Al2O3 has been considered. Catalyst activation is characterized in terms of temperature programmed reduction, the supported nano-scale metal phase by transmission electron microscopy and hydrogen/surface interactions by chemisorption/temperature programmed desorption. Pd/Al2O3 generated significantly greater amounts of spillover hydrogen (by a factor of over 40) compared with Ni/Al2O3. Hydrogen spillover on Pd/Al2O3 far exceeded the chemisorbed component, whereas chemisorbed and spillover content was equivalent for Ni/Al2O3. Inclusion of Al2O3 with Ni and Ni/Al2O3 increased spillover with an associated increase in specific HOC rate (up to a factor of 10) and enhanced selectivity to benzene from 1,3-DCB. HDC rate delivered by Pd and Pd/Al2O3 was largely unaffected by the addition of Al2O3. This can be attributed to the higher intrinsic HOC performance of Pd that results in appreciable HOC activity under conditions where Ni/Al2O3 was inactive. Spillover was partially recovered (post TPD) for the Ni samples but the loss was irreversible in the case of Pd. (c) 2011 Elsevier B.V. All rights reserved.