Carbon nanofibers (CNFs) are treated with ammonia at elevated temperatures to generate pyridinic-type basic species on the CNFs surface. The basic species act as anchors for Pd nanoparticles, resulting in good dispersion and stability of the Pd nanoparticles. These ammonia-treated carbon nanofibers as Pd supports have been used for catalytic hydrodechlorination. It shows high activity and impressive time-on-stream stability in the gas- and liquid-phase catalytic hydrodechlorination of chlorobenzene. The presence of pyridine-type species helps to remove the byproduct HCl from the Pd catalyst, thus preventing the inhibition effect of HCl. It also keeps Pd nanoparticles from aggregation, which is another reason for catalyst deactivation.