The hydrodechlorination of 2-chlorobiphenyl promoted by a commercial Ni-Mo catalyst has been investigated in a stirred batch reactor (T = 300 degreesC and P = 20 bar) in order to analyze the mass-transfer resistances which might influence the performance of an industrial reactor. Powdered (diameter congruent to 100 mum) and full size particles (cylinders diameter = 3 mm; length = 4.5 mm) catalysts have been used. In the second case, a rotating basket reactor has been set up. The results of the investigation indicate that external mass-transfer resistances are not relevant in the majority of the cases. When catalyst pellets are adopted, the diffusion in the catalyst porosity plays a significant role and values of the effectiveness factor in the range 0.05-0.12 have been calculated.