The catalytic hydrodechlorination of four trichlorophenol (TCP) isomers (2,3,5-TCP, 2,3,6-TCP, 2,4,5-TCP and 2,4,6-TCP) was studied in the gas phase using an Ni/SiO2 catalyst over the temperature range 473 K less than or equal to T less than or equal to 573 K. The catalyst was 100% selective in removing chlorine(s), leaving the hydroxyl group and benzene ring intact. Dechlorination proceeds via stepwise and concerted routes and the relative importance of each is dependent on the nature of the isomer where steric rather than resonance effects appear to determine the ultimate product distribution. Dechlorination efficiency is quantified in terms of phenol yield, chlorine removal rate and the ultimate partitioning of chlorine in the parent organic or product inorganic host. The reaction pathways, with associated pseudo-first order rate constants, for the conversion of 2,3,6-TCP and 2,4,6-TCP are presented. The effect of time and temperature on process selectivity is discussed and the nature of catalyst deactivation is considered.